TY - GEN A1 - Klein, Marten A1 - Lignell, David O. A1 - Schmidt, Heiko T1 - Stochastic modeling of transient surface scalar and momentum fluxes in turbulent boundary layers T2 - EMS Annual Meeting 2021, online, 6–10 Sep 2021, EMS2021-79 N2 - Turbulence is ubiquitous in atmospheric boundary layers and manifests itself by transient transport processes on a range of scales. This range easily reaches down to less than a meter, which is smaller than the typical height of the first grid cell layer adjacent to the surface in numerical models for weather and climate prediction. In these models, the bulk-surface coupling plays an important role for the evolution of the atmosphere but it is not feasible to fully resolve it in applications. Hence, the overall quality of numerical weather and climate predictions crucially depends on the modeling of subfilter-scale transport processes near the surface. A standing challenge in this regard is the robust but efficient representation of transient and non-Fickian transport such as counter-gradient fluxes that arise from stratification and rotation effects. We address the issues mentioned above by utilizing a stochastic one-dimensional turbulence (ODT) model. For turbulent boundary layers, ODT aims to resolve the wall-normal transport processes on all relevant scales but only along a single one-dimensional domain (column) that is aligned with the vertical. Molecular diffusion and unbalanced Coriolis forces are directly resolved, whereas effects of turbulent advection and stratification are modeled by stochastically sampled sequence of mapping (eddy) events. Each of these events instantaneously modifies the flow profiles by a permutation of fluid parcels across a selected size interval. The model is of lower order but obeys fundamental conservation principles and Richardson's 1/4 law by construction. In this study, ODT is applied as stand-alone tool in order to investigate nondimensional control parameter dependencies of the scalar and momentum transport in turbulent channel, neutral, and stably-stratified Ekman flows up to (friction) Reynolds number Re = O(104). We demonstrate that ODT is able to capture the state-space statistics of transient surface fluxes as well as the boundary-layer structure and nondimensional control parameter dependencies of low-order flow statistics. Very good to reasonable agreement with available reference data is obtained for various observables using fixed model set-ups. We conclude that ODT is an economical turbulence model that is able to not only capture but also predict the wall-normal transport and surface fluxes in multiphysics turbulent boundary layers. KW - one-dimensional turbulence KW - stochastic modeling KW - Ekman flow KW - atmospheric boundary layer KW - roating and stratified fluids Y1 - 2021 UR - https://doi.org/10.5194/ems2021-79 UR - https://www.b-tu.de/media/video/Stochastic-modeling-of-transient-surface-scalar-and-momentum-fluxes-in-turbulent-boundary-layers/8c7baf58c040239649fb7c3b2212c1d5 U6 - https://doi.org/10.5194/ems2021-79 ER - TY - GEN A1 - Klein, Marten A1 - Schmidt, Heiko A1 - Lignell, David O. T1 - Stochastic modeling of transient surface scalar and momentum fluxes in turbulent boundary layers, EMS Annual Meeting 2021, online, 6–10 Sep 2021 KW - one-dimensional turbulence KW - stochastic modeling KW - Ekman flow KW - atmospheric boundary layer KW - roating and stratified fluids Y1 - 2021 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Klein_poster_ems21.pdf UR - https://www.b-tu.de/media/video/Stochastic-modeling-of-transient-surface-scalar-and-momentum-fluxes-in-turbulent-boundary-layers/8c7baf58c040239649fb7c3b2212c1d5 ER - TY - GEN A1 - Klein, Marten A1 - Schmidt, Heiko ED - Wagner, Claus T1 - Stochastic modeling and simulation of turbulent boundary layers in annular channel flow using one-dimensional turbulence T2 - STAB Jahresbericht 2021 N2 - In our contribution to the STAB workshop we will present the ODT model formulation with an emphasis on turbulent eddy energetics and map-based advection modeling in radial direction. After that, we will address ODT’s capabilities for simulation of turbulent boundary layers in planar and annular channel flows in terms of conventional turbulence statistics and bulk quantities. Last, we will address the effects of radius ratio and Reynolds number variations. KW - one-dimensional turbulence KW - stochastic modeling KW - spanwise curvature effects KW - radial momentum transport KW - boundary layers KW - coaxial pipe flow Y1 - 2021 UR - https://www.dlr.de/as/desktopdefault.aspx/tabid-128/268_read-1678/ UR - https://www.dlr.de/as/Portaldata/5/Resources/dokumente/veranstaltungen/stab_workshop/STAB-Jahresbericht-2021.pdf VL - 2021 SP - 39 EP - 40 PB - Deutsche Strömungsmechanische Arbeitsgemeinschaft, STAB CY - Göttingen ER - TY - GEN A1 - Klein, Marten A1 - Schmidt, Heiko A1 - Lignell, David O. T1 - Stochastic modeling of surface scalar-flux fluctuations in turbulent channel flow using one-dimensional turbulence T2 - International Journal of Heat and Fluid Flow N2 - Accurate and economical modeling of near-surface transport processes is a standing challenge for various engineering and atmospheric boundary-layer flows. In this paper, we address this challenge by utilizing a stochastic one-dimensional turbulence (ODT) model. ODT aims to resolve all relevant scales of a turbulent flow for a one-dimensional domain. Here ODT is applied to turbulent channel flow as stand-alone tool. The ODT domain is a wall-normal line that is aligned with the mean shear. The free model parameters are calibrated once for the turbulent velocity boundary layer at a fixed Reynolds number. After that, we use ODT to investigate the Schmidt (Sc), Reynolds (Re), and Peclet (Pe) number dependence of the scalar boundary-layer structure, turbulent fluctuations, transient surface fluxes, mixing, and transfer to a wall. We demonstrate that the model is able to resolve relevant wall-normal transport processes across the turbulent boundary layer and that it captures state-space statistics of the surface scalar-flux fluctuations. In addition, we show that the predicted mean scalar transfer, which is quantified by the Sherwood (Sh) number, self-consistently reproduces established scaling regimes and asymptotic relations. For high asymptotic Sc and Re, ODT results fall between the Dittus-Boelter, Sh ∼ Re^(4/5) Sc^(2/5), and Colburn, Sh ∼ Re^(4/5) Sc^(1/3), scalings but they are closer to the former. For finite Sc and Re, the model prediction reproduces the relation proposed by Schwertfirm and Manhart (Int. J. Heat Fluid Flow, vol. 28, pp. 1204-1214, 2007) that yields locally steeper effective scalings than any of the established asymptotic relations. The model extrapolates the scalar transfer to small asymptotic Sc ≪ Re_τ^(-1) (diffusive limit) with a functional form that has not been previously described. KW - one-dimensional turbulence KW - stochastic modeling KW - fluctuation modeling KW - passive scalar KW - scalar transfer KW - Schmidt number dependence KW - surface flux Y1 - 2021 UR - https://arxiv.org/abs/2111.15359 U6 - https://doi.org/10.1016/j.ijheatfluidflow.2021.108889 SN - 0142-727X VL - 93 (2022) SP - 1 EP - 19 ER - TY - GEN A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Investigating Schmidt number effects in turbulent electroconvection using one-dimensional turbulence T2 - Proc. Appl. Math. Mech. N2 - Turbulent electroconvection denotes a fluctuating multiphysical flow in which hydrodynamics and electrokinetics interact on multiple scales. The dynamical processes at work are entangled down to the molecular-diffusive scales that are determined by the Schmidt (Sc) and Reynolds (Re) number. Turbulence properties are generally nonuniversal which leads to high numerical resolution requirements. We address the numerical challenges associated with accuracy and feasibility by utilizing a stochastic one-dimensional turbulence (ODT) model. Here, ODT is applied to turbulent Couette flow of dilute electrolytes as canonical problem for turbulent electroconvection. For Sc ⩾ O(10), ODT predicts an increase of the skin friction drag due to electrohydrodynamically (EHD) enhanced small-scale eddy production once the flow is sufficiently turbulent. KW - one-dimensional turbulence KW - stochastic modeling KW - turbulent Couette flow KW - electrohydrodynamic turbulence KW - Schmidt number effects KW - skin friction drag Y1 - 2021 U6 - https://doi.org/https://doi.org/10.1002/pamm.202100147 VL - 21 SP - 1 EP - 3 PB - Wiley CY - Weinheim ER - TY - GEN A1 - Klein, Marten A1 - Maier, Roland Erich A1 - Schmidt, Heiko T1 - Stochastic modeling of transient neutral and stably-stratified Ekman boundary layers T2 - Special Issue: 92nd Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM) N2 - Neutral and stably-stratified Ekman boundary layers (EBLs) are numerically investigated with a stochastic one-dimensional turbulence (ODT) model. EBLs achieve the bulk-surface coupling in Earth's atmosphere. They are numerically challenging due to transient and non-universal turbulence properties even at small scales. ODT addresses this problem by distinguishing turbulent-advective from molecular-diffusive transport processes for a vertical column along which all relevant scales of the flow are resolved. We demonstrate the model's capabilities for economical, accurate, and stratification regime independent simulation of EBLs for the wind-turning angle. ODT reproduces and extrapolates reference direct numerical simulation results consistent with observations. We conclude that ODT may be useful for modeling of atmospheric surface layers. KW - one-dimensional turbulence KW - stochastic modeling KW - turbulent Ekman flow KW - roating and stratified fluids KW - transition Y1 - 2021 U6 - https://doi.org/10.1002/pamm.202100146 VL - 21 SP - 1 EP - 3 PB - Wiley CY - Weinheim ER - TY - GEN A1 - Klein, Marten A1 - Freire, Livia S. A1 - Lignell, David O. A1 - Kerstein, Alan R. A1 - Schmidt, Heiko T1 - Ein stochastischer Ansatz zur Modellierung fluktuierender Oberflächenflüsse in turbulenten Grenzschichten T2 - Kurzfassungen der Meteorologentagung DACH N2 - Im Konferenzbeitrag wird auf die Formulierung des stochastischen Modells eingegangen und gezeigt, dass neben Scherspannungen auch Druck-, Coriolis- und Auftriebskräfte berücksichtigt werden können. Das Modell wird beispielhaft als unabhängiges, numerisches Werkzeug angewendet, um fluktuierende Oberflächenflüsse in turbulenten Kanalströmungen sowie stabilen und konvektiven Grenzschichten zu untersuchen. Es werden sowohl glatte, als auch raue bzw. bewachsene (poröse) Oberflächen betrachtet. Anhand neuer Ergebnisse wird demonstriert, dass der Modellansatz in der Lage ist, Referenzdaten zufriedenstellend zu reproduzieren und extrapolieren. Daneben werden aktuelle Arbeiten zur Kopplung des stochastischen Modellansatzes mit Large-Eddy-Simulationen vorgestellt. Es wird gezeigt, dass die stochastische Modellierung oberflächennaher, subgitterskaliger Schwankungen in der Lage ist, wandnahe Turbulenzspektren zu reproduzieren und den filterbasierten Modellfehler bei ansonsten fester Gitterauflösung zu verringern. KW - one-dimensional turbulence KW - stochastic modeling KW - turbulent boundary layer KW - turbulent convection KW - rotating and stratified flows Y1 - 2021 UR - https://meetingorganizer.copernicus.org/DACH2022/DACH2022-22.html U6 - https://doi.org/10.5194/dach2022-22 VL - 2022 SP - 1 EP - 1 PB - Copernicus ER - TY - GEN A1 - Sharma, Sparsh A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Modelling turbulent jets at high-Reynolds number using one-dimensional turbulence T2 - AIAA AVIATION 2021 FORUM KW - stochastic modeling KW - turbulent round jet KW - one-dimensional turbulence Y1 - 2021 UR - https://arc.aiaa.org/doi/abs/10.2514/6.2021-2104 SN - 978-1-62410-610-1 U6 - https://doi.org/10.2514/6.2021-2104 PB - American Institute of Aeronautics and Astronautics, Inc. ER - TY - GEN A1 - Sharma, Sparsh A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Features of far-downstream asymptotic velocity fluctuations in a round jet: A one-dimensional turbulence study T2 - Physics of Fluids KW - stochastic modeling KW - turbulent round jet KW - one-dimensional turbulence KW - jet similarity KW - multi-scale fluctuation modeling Y1 - 2022 UR - https://aip.scitation.org/doi/10.1063/5.0101270 U6 - https://doi.org/10.1063/5.0101270 SN - 1089-7666 VL - 34 IS - 8 ER - TY - GEN A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Stochastic modeling of transient Ekman flow at arbitrary Reynolds number driven by horizontal bottom wall oscillation T2 - EMS Annual Meeting 2022, Abstracts KW - stochastic modeling KW - one-dimensional turbulence KW - rotating boundary layers KW - intermittency Y1 - 2022 U6 - https://doi.org/10.5194/ems2022-617 VL - 19 PB - Copernicus CY - Bonn, Germany ER - TY - GEN A1 - Tsai, Pei-Yun A1 - Schmidt, Heiko A1 - Klein, Marten T1 - Modeling simultaneous momentum and passive scalar transfer in turbulent annular Poiseuille flow T2 - 92nd Annual Meeting of GAMM KW - stochastic modeling KW - one-dimensional turbulence KW - heat and mass transfer KW - skin friction drag KW - forced convection KW - spanwise wall curvature Y1 - 2022 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Klein_2022_coaxialPipe_GAMM_abstract.pdf UR - https://jahrestagung.gamm-ev.de/wp-content/uploads/2022/08/Daily_Program_Web.pdf PB - Gesellschaft für angewandte Mathematik und Mechanik e.V. CY - Aachen, Germany ER - TY - GEN A1 - Klein, Marten A1 - Tsai, Pei-Yun A1 - Schmidt, Heiko T1 - Stochastic modeling of heat and momentum transfer in annular pipe flow: A one-dimensional turbulence study with comparison to DNS and LES T2 - STAB Jahresbericht 2022 KW - stochastic modeling KW - one-dimensional turbulence KW - heat and mass transfer KW - turbulent Poiseuille flow KW - large-eddy simulation Y1 - 2022 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Klein_2022_STAB_abstract.pdf UR - https://www.dlr.de/as/desktopdefault.aspx/tabid-128/268_read-1678/ UR - https://www.dlr.de/as/Portaldata/5/Resources/dokumente/veranstaltungen/stab_workshop/Jahresbericht2022.pdf VL - 23 PB - Deutsche Strömungsmechanische Arbeitsgemeinschaft (STAB) CY - Göttingen, Germany ER - TY - GEN A1 - Klein, Marten A1 - Medina Méndez, Juan Alí A1 - Schmidt, Heiko T1 - Modeling electrohydrodynamically enhanced drag in channel and pipe flows using one-dimensional turbulence T2 - Conference on Modelling Fluid Flow (CMFF’22) KW - stochastic modeling KW - one-dimensional turbulence KW - turbulent drag enhancement KW - electrohydrodynamic turbulence KW - multiphysical boundary layers Y1 - 2022 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Klein_cmff22_abstract_EHDdrag.pdf UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Klein_cmff22_paper_submitted_EHDdrag.pdf UR - https://www.cmff.hu/pdf/FinalProgramme.pdf SP - 1 EP - 8 CY - Budapest, Hungary ER - TY - GEN A1 - Klein, Marten A1 - Medina Méndez, Juan Alí A1 - Schmidt, Heiko ED - Vad, Janos T1 - Modeling electrohydrodynamically enhanced drag in channel and pipe flows using One-Dimensional Turbulenc T2 - Proceedings of the Conference on Modelling Fluid Flow (CMFF’22) N2 - The joint modeling of flow hydrodynamics and electrokinetics is a relatively unexplored area of turbulent flow research. We address a lack of available models for electrohydrodynamic (EHD) turbulent flow utilizing a lower-order approach, the stochastic One-Dimensional Turbulence (ODT) model. ODT is constructed on the principles of the direct energy cascade of Navier–Stokes turbulence, with key emphasis on the accurate resolution of the small molecular transport scales within a notional line-of-sight. We investigate two canonical flow configurations to demonstrate the applicability of the model in the simulation of EHD flows. First, we investigate EHD effects in zero-pressure-gradient turbulent boundary layers by two-way coupled model application to plane Couette flow of a dilute electrolyte. Second, we apply the one-way coupled model to EHD-enhanced gas flow through a vertical pipe with an inner concentric electrode, where electric fields are generated by means of a corona discharge and the corresponding effect of a continuum ionic charge density field. KW - EHD turbulence KW - multiphysical boundary layers KW - one-dimensional turbulence KW - stochastic modeling KW - turbulent drag enhancement Y1 - 2022 UR - https://www.cmff.hu/pdf/CMFF22_Conference_Proceedings.pdf UR - https://www.cmff.hu/papers/CMFF22_Final_Paper_PDF_15.pdf SN - 978-963-421-881-4 SP - 82 EP - 91 PB - University of Technology and Economics, Department of Fluid Mechanics CY - Budapest, Hungary ER - TY - GEN A1 - Klein, Marten A1 - Zenker, Christian A1 - Starick, Tommy A1 - Schmidt, Heiko T1 - Stochastic modeling of three-scalar mixing in a coaxial jet using one-dimensional turbulence T2 - 12th International Symposium on Turbulence and Shear Flow Phenomena (TSFP12), Osaka, Japan (Online), July 19-22, 2022 N2 - Modeling complex mixing processes is a standing challenge for a number of applications ranging from chemical to mechanical and environmental engineering. Here, the gas-phase turbulent mixing in a three-stream concentric coaxial jet is investigated as a canonical problem. Reynolds-averaged Navier–Stokes simulations (RANS) suggest that the gas-phase mixing can be accurately modeled by air doped with passive scalars, for which small-scale resolving numerical simulations are performed with the one-dimensional turbulence (ODT) model as stand-alone tool. We show that both the spatial (S-ODT) and temporal (T-ODT) model formulations yield qualitatively similar results exhibiting reasonable to good agreement with available reference experiments, Reynolds-averaged and large-eddy simulations, as well as mixing models. This is demonstrated for low-order statistics, like the scalar variance and dissipation, but also the two-scalar joint probability density functions that can not be obtained with RANS. Our results suggest that S-ODT has better capabilities than T-ODT to model the mixing processes in the jet which we attribute to the account of local advective time scales. KW - stochastic modeling KW - one-dimensional turbulence KW - concentric coaxial round jet KW - multiple passive scalars KW - turbulent mixing KW - co-flow entrainment Y1 - 2022 UR - http://www.tsfp-conference.org/proceedings/2022/208.pdf UR - http://www.tsfp-conference.org/proceedings/proceedings-of-tsfp-12-2022-osaka.html N1 - Contribution No. 6 of 7 in Session 13C: Jets II SP - 1 EP - 6 ER - TY - GEN A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Exploring stratification effects in stable Ekman boundary layers using a stochastic one-dimensional turbulence model T2 - Advances in Science and Research N2 - Small-scale processes in atmospheric boundary layers are typically not resolved due to cost constraints but modeled based on physical relations with the resolved scales, neglecting expensive backscatter. This lack in modeling is addressed in the present study with the aid of the one-dimensional turbulence (ODT) model. ODT is applied as stand-alone column model to numerically investigate stratification effects in long-lived transient Ekman flows as canonical example of polar boundary layers by resolving turbulent winds and fluctuating temperature profiles on all relevant scales of the flow. We first calibrate the adjustable model parameters for neutral cases based on the surface drag law which yields slightly different optimal model set-ups for finite low and moderate Reynolds numbers. For the stably stratified cases, previously calibrated parameters are kept fixed and the model predictions are compared with various reference numerical simulations and also observations by an exploitation of boundary layer similarity. ODT reasonably captures the temporally developing flow for various prescribed stratification profiles, but fails to fully capture the near-surface laminarization by remaining longer in a fully developed turbulent state, which suggests preferential applicability to high-Reynolds-number flow regimes. Nevertheless, the model suggests that large near-surface turbulence scales are primarily affected by the developing stratification due to scale-selective buoyancy damping which agrees with the literature. The variability of the wind-turning angle represented by the ensemble of stratified cases simulated covers a wider range than reference reanalysis data. The present study suggests that the vertical-column ODT formulation that is highly resolved in space and time can help to accurately represent multi-physics boundary-layer and subgrid-scale processes, offering new opportunities for analysis of very stable polar boundary layer and atmospheric chemistry applications. KW - stochastic turbulence modeling KW - one-dimensional turbulence KW - stable stratification KW - atmospheric boundary layer KW - wind veering angle KW - Richardson number Y1 - 2022 UR - https://asr.copernicus.org/articles/19/117/2022/ U6 - https://doi.org/10.5194/asr-19-117-2022 SN - 1992-0636 N1 - This article is part of the special issue “21st EMS Annual Meeting – virtual: European Conference for Applied Meteorology and Climatology 2021”. VL - 19/2022 SP - 117 EP - 136 ER - TY - GEN A1 - Schmidt, Heiko A1 - Klein, Marten T1 - Chair of Numerical Fluid and Gas Dynamics KW - numerical fluid and gas dynamics KW - transfer processes KW - stochastic modeling and simulation KW - overview of research areas Y1 - 2022 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Klein_poster_nsg+yig_hu-btu22.pdf ER - TY - GEN A1 - Hartmann, Carsten A1 - Köhler, Ekkehard A1 - Schmidt, Heiko A1 - Klein, Marten T1 - Scientific computing LAB (SCL) T2 - "Get Into Energy", BTU Cottbus-Senftenberg, ZHG Building, 1 Feb. 2023 N2 - KEY COMPETENCE AND FOCUS • Development of numerical methods and algorithms for multi-energy systems • Multiscale and multiphysics modeling and simulation of P2X technologies • Stochastic simulation and efficient optimization of complex energy networks KW - Energy Innovation Center (EIZ) KW - Scientific Computing Lab (SCL) KW - P2X KW - multiphysics multiscale problems KW - stochastic modeling and simulation KW - network optimization Y1 - 2023 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Poster_SCL_seed_v3.pdf CY - Cottbus ER - TY - GEN A1 - Tsai, Pei-Yun A1 - Schmidt, Heiko A1 - Klein, Marten T1 - Stochastic modeling of heated turbulent coaxial pipe flow prescribing different thermal boundary conditions T2 - 18th European Turbulence Conference (ETC18), 4-6 September 2023, Valencia Y1 - 2023 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Tsai_2023_ETC18_abstract.pdf UR - https://etc18.webs.upv.es/wp-content/uploads/2023/08/Program_final_impresion.pdf CY - Valencia ER - TY - GEN A1 - Medina Méndez, Juan Alí A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Fractal roughness representation in a stochastic one-dimensional turbulence modeling approach T2 - Book of Abstracts 13th International Symposium on Turbulence and Shear Flow Phenomena (TSFP13), Montréal, Canada, June 25-28, 2024 Y1 - 2024 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Medina_2024_TSFP13_Roughness_PFA_ODT.pdf CY - Montréal, Canada ER - TY - GEN A1 - Naik Burye, Nishidh Shailesh A1 - Medina Méndez, Juan Alí A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Revisiting near-wall modeling of fully developed turbulent flow in concentric annuli T2 - Jahresbericht 2024 zum 24. DGLR-Fachsymposium der STAB 13.-14. November 2024, Regensburg Y1 - 2024 UR - http://bfm.rcbe.de/files/2024/11/2024_STAB-Jahresbericht.pdf SP - 174 EP - 175 PB - Deutsche Strömungsmechanische Arbeitsgemeinschaft, STAB CY - Regensburg ER - TY - GEN A1 - Polasanapalli, Sai Ravi Gupta A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Numerical study on the effects of transient pressure gradients on isothermal and heated pipe flows T2 - 94th Annual Meeting of the Association of Applied Mathematics and Mechanics March 18th-March 22nd, 2024 Magdeburg (Germany) : Book of Abstracts Y1 - 2024 UR - https://jahrestagung.gamm.org/wp-content/uploads/2024/03/BookOfAbstracts-1.pdf SP - 227 EP - 228 CY - Magdeburg (Germany) ER - TY - GEN A1 - Joshi, Abhishek A1 - Medina Mendez, Juan Ali A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Simulating homogenous isotropic turbulence with deterministic and stochastic forcings using a one-dimensional turbulence model N2 - To understand the intermittency present in scalar fields we need to address the expense of current start-of-art DNS to probe the higher-order structure functions. These higher order moments become increasingly sensitive to increasing Reλ and much more prone to extreme events. Here, in this work, we investigate using a Reduced order model(ODT) to simulate Homogenous Isotropic turbulence as an initial step towards that goal by employing a linear forcing [1] proposed by Lundgren that is proportional to local and instantaneous velocity. Y1 - 2024 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Joshi_2024_MFM_Poster.pdf ER - TY - GEN A1 - Marinković, Pavle A1 - Medina Méndez, Juan Ali A1 - Schmidt, Heiko A1 - Klein, Marten T1 - Ongoing development of a hybrid reduced order stochastic/LES solver for turbulent flows Y1 - 2024 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Marinkovic_2024_EIZ_poster.pdf CY - Cottbus ER - TY - GEN A1 - Tsai, Pei-Yun A1 - Schmidt, Heiko A1 - Klein, Marten T1 - Stochastic modeling and theoretical analysis of heated concentric coaxial pipes at low Prandtl number T2 - 94rd Annual Meeting of the International Association of Applied Mathematics and Mechanics, Book of Abstracts Y1 - 2024 UR - https://jahrestagung.gamm.org/wp-content/uploads/2024/03/BookOfAbstracts-2.pdf PB - GAMM e.V. CY - Magdeburg ER - TY - GEN A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Time-resolved simulations of wind speed fluctuations across atmospheric boundary layers using a stochastic forward model T2 - Verhandlungen der DPG Frühjahrstagung SMuK 2023 N2 - Atmospheric boundary layers (ABLs) govern the atmosphere–surface coupling and are therefore of fundamental relevance for Earth’s weather and climate system. Time-resolved numerical simulations of ABLs are challenging due to intricate interactions of inertial, Coriolis, buoyancy, and viscous forces on all relevant scales of the turbulent flow. Small-scale processes, albeit potentially nonuniversal, are typically not resolved due to cost constraints but modeled based on physically justified relations with the resolved scales, neglecting expensive backscatter. This lack in modeling is addressed here by utilizing a dimensionally reduced stochastic modeling approach. The model aims to reproduce turbulent cascade phenomenology by a stochastic process, respecting fundamental physical conservation principles. Momentary wind velocity and temperature profiles evolve autonomously in time for an ensemble of initial conditions. By comparison with available high-fidelity reference numerical simulations, reanalysis, and observations, it is shown that the model captures various relevant flow properties, exhibiting limitations mainly in a delayed relaminarization under very stable conditions. Forthcoming research aims to contribute to a better understanding of polar boundary layers, requiring predictive modeling capabilities, high resolution, and numerical efficiency to perform long-time simulations. KW - wind energy KW - stochastic forward modeling KW - one-dimensional turbulence KW - time-series prediction and modeling KW - atmospheric boundary layer Y1 - 2023 UR - https://www.dpg-verhandlungen.de/year/2023/conference/smuk/part/up/session/5/contribution/3 PB - Deutsche Physikalische Gesellschaft (DPG) CY - Dresden ER - TY - GEN A1 - Tsai, Pei-Yun A1 - Schmidt, Heiko A1 - Klein, Marten T1 - Modeling simultaneous momentum and passive scalar transfer in turbulent annular Poiseuille flow T2 - Proceedings in applied mathematics and mechanics : PAMM N2 - Simultaneous momentum and passive scalar transfer in weakly heated pressure-driven turbulent concentric annular pipe flow is numerically investigated using the cylindrical formulation of the stochastic one-dimensional turbulence (ODT) model,which is utilized here as standalone tool. In the present study, we focus on the model calibration for heated annular pipes based on recent reference direct numerical simulations (DNS) from Bagheri and Wang (Int. J. Heat Fluid Flow 86, 108725,2020; Phys. Fluids 33, 055131, 2021). It is shown that the model is able to individually capture scalar and momentum transfer, but not both equally well at the same time. We attribute this to less dissimilar scalar and momentum transport in the model at the low Reynolds number investigated. It is argued that the model prefers a fully developed turbulent state due to its construction. Nevertheless, it is demonstrated that ODT is able to reasonably capture the radial inner-outer asymmetry of the scalar and momentum boundary layers which yields better predictive capabilities than wall-function-based approaches. KW - turbulent heat and mass transfer KW - heated pipe flow KW - one-dimensional turbulence KW - stochastic turbulence modeling KW - turbulent drag KW - spanwise curvature effects Y1 - 2023 UR - https://onlinelibrary.wiley.com/doi/10.1002/pamm.202200272 U6 - https://doi.org/10.1002/pamm.202200272 SN - 1617-7061 N1 - Special Issue: 92nd Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM) VL - 22 IS - 1 ER - TY - GEN A1 - Gao, Tianyun A1 - Schmidt, Heiko A1 - Klein, Marten A1 - Liang, Jianhan A1 - Sun, Mingbo A1 - Chen, Chongpei A1 - Guan, Qingdi T1 - One-dimensional turbulence modeling of compressible flows. I. Conservative Eulerian formulation and application to supersonic channel flow T2 - Physics of Fluids N2 - Accurate but economical modeling of supersonic turbulent boundary layers is a standing challenge due to the intricate entanglement of temperature, density, and velocity fluctuations on top of the mean-field variation. Application of the van Driest transformation may describe well the mean state but cannot provide detailed flow information. This lack-in modeling coarse and fine-scale variability is addressed by the present study using a stochastic one-dimensional turbulence (ODT) model. ODT is a simulation methodology that represents the evolution of turbulent flow in a low-dimensional stochastic way. In this study, ODT is extended to fully compressible flows. An Eulerian framework and a conservative form of the governing equations serve as the basis of the compressible ODT model. Computational methods for statistical properties based on ODT realizations are also extended to compressible flows, and a comprehensive way of turbulent kinetic energy budget calculation based on compressible ODT is put forward for the first time. Two canonical direct numerical simulation cases of supersonic isothermal-wall channel flow at Mach numbers 1.5 and 3.0 with bulk Reynolds numbers 3000 and 4880, respectively, are used to validate the extended model. A rigorous numerical validation is presented, including the first-order mean statistics, the second-order root mean square statistics, and higher-order turbulent fluctuation statistics. In ODT results, both mean and root mean square profiles are accurately captured in the near-wall region. Near-wall temperature spectra reveal that temperature fluctuations are amplified at all turbulent scales as the effects of compressibility increase. This phenomenon is caused by intensified viscous heating at a higher Mach number, which is indicated by the steeper profiles of viscous turbulent kinetic energy budget terms in the very near-wall region. The low computational cost and predictive capabilities of ODT suggest that it is a promising approach for detailed modeling of highly turbulent compressible boundary layers. Furthermore, it is found that the ODT model requires a Mach-number-dependent increase in a viscous penalty parameter Z in wall-bounded turbulent flows to enable accurate capture of the buffer layer. KW - supersonic turbulent channel flow KW - stochastic turbulence modeling KW - one-dimensional turbulence KW - compressibility effects KW - turbulent boundary layer Y1 - 2023 U6 - https://doi.org/10.1063/5.0125514 SN - 1089-7666 VL - 35 IS - 3 ER - TY - GEN A1 - Gao, Tianyun A1 - Schmidt, Heiko A1 - Klein, Marten A1 - Liang, Jianhan A1 - Sun, Mingbo A1 - Chen, Chongpei A1 - Guan, Qingdi T1 - One-dimensional turbulence modeling of compressible flows: II. Full compressible modification and application to shock–turbulence interaction T2 - Physics of Fluids N2 - One-dimensional turbulence (ODT) is a simulation methodology that represents the essential physics of three-dimensional turbulence through stochastic resolution of the full range of length and time scales on a one-dimensional domain. In the present study, full compressible modifications are incorporated into ODT methodology, based on an Eulerian framework and a conservative form of the governing equations. In the deterministic part of this approach, a shock capturing scheme is introduced for the first time. In the stochastic part, one-dimensional eddy events are modeled and sampled according to standard methods for compressible flow simulation. Time advancement adjustments are made to balance comparable time steps between the deterministic and stochastic parts in compressible flows. Canonical shock–turbulence interaction cases involving Richtmyer–Meshkov instability at Mach numbers 1.24, 1.5, and 1.98 are simulated to validate the extended model. The ODT results are compared with available reference data from large eddy simulations and laboratory experiments. The introduction of a shock capturing scheme significantly improves the performance of the ODT method, and the results for turbulent kinetic energy are qualitatively improved compared with those of a previous compressible Lagrangian ODT method [Jozefik et al., “Simulation of shock–turbulence interaction in non-reactive flow and in turbulent deflagration and detonation regimes using one-dimensional turbulence,” Combust. Flame 164, 53 (2016)]. For the time evolution of profiles of the turbulent mixing zone width, ensemble-averaged density, and specific heat ratio, the new model also yields good to reasonable results. Furthermore, it is found that the viscous penalty parameter Z of the ODT model is insensitive to compressibility effects in turbulent flows without wall effects. A small value of Z is appropriate for turbulent flows with weak wall effects, and the parameter Z serves to suppress extremely small eddy events that would be dissipated instantly by viscosity. KW - shock-turbulence interaction KW - stochastic turbulence modeling KW - one-dimensional turbulence KW - Richtmyer-Meshkov instability Y1 - 2023 U6 - https://doi.org/10.1063/5.0137435 SN - 1089-7666 VL - 35 IS - 3 ER - TY - GEN A1 - Klein, Marten A1 - Schöps, Mark Simon A1 - Medina Méndez, Juan Alí A1 - Schmidt, Heiko T1 - Numerical simulation and analysis of transient Ekman boundary layers using a stochastic turbulence model T2 - EGU General Assembly 2023 KW - stochastic modeling KW - one-dimensional turbulence KW - turbulent Ekman flow KW - transient boundary layer Y1 - 2023 UR - https://meetingorganizer.copernicus.org/EGU23/EGU23-9116.html U6 - https://doi.org/10.5194/egusphere-egu23-9116 PB - EGU - European Geophysical Union CY - Vienna, Austria ER - TY - GEN A1 - Glawe, Christoph A1 - Klein, Marten A1 - Schmidt, Heiko T1 - ODT augmented RaNS T2 - Book of Abstracts of the 93rd Annual Meeting of the International Association of Applied Mathematics and Mechanics KW - turbulence modeling KW - one-dimensional turbulence KW - Reynolds-averaged Navier-Stokes simulation KW - boundary layer KW - stochastic post-processing Y1 - 2023 UR - https://jahrestagung.gamm-ev.de/wp-content/uploads/2023/05/20230517_BookofAbstracts_final_red.pdf SP - 368 PB - GAMM e.V. CY - Dresden ER - TY - GEN A1 - Medina Méndez, Juan Alí A1 - Sharma, Sparsh A1 - Schmidt, Heiko A1 - Klein, Marten T1 - Towards the use of a reduced order and stochastic turbulence model for assessment of far-field sound radiation: low Mach number jet flows T2 - Book of Abstracts of the 93rd Annual Meeting of the International Association of Applied Mathematics and Mechanics KW - turbulent noise sources KW - reduced-order modeling KW - one-dimensional turbulence KW - turbulent jet KW - stochastic modeling and simulation Y1 - 2023 UR - https://jahrestagung.gamm-ev.de/wp-content/uploads/2023/05/20230517_BookofAbstracts_final_red.pdf SP - 413 EP - 414 PB - GAMM e.V. CY - Dresden ER - TY - GEN A1 - Sharma, Sparsh A1 - Ayton, Lorna A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Estimation of ODT-resolved acoustic sources in high Reynolds number turbulent jets T2 - Book of Abstracts of the 93rd Annual Meeting of the International Association of Applied Mathematics and Mechanics KW - stochastic modeling KW - turbulent jet KW - turbulent acoustic sources KW - noise modeling KW - one-dimensional turbulence Y1 - 2023 UR - https://jahrestagung.gamm-ev.de/wp-content/uploads/2023/05/20230517_BookofAbstracts_final_red.pdf SP - 414 EP - 415 PB - GAMM e.V. CY - Dresden ER - TY - GEN A1 - Polasanapalli, Sai Ravi Gupta A1 - Klein, Marten A1 - Schmidt, Heiko T1 - SGS modeling in lattice Boltzmann method for non-fully resolved turbulent flows T2 - Book of Abstracts of the 93rd Annual Meeting of the International Association of Applied Mathematics and Mechanics KW - lattice Boltzmann method KW - subgrid-scale modeling KW - model comparison KW - thermal convection Y1 - 2023 UR - https://jahrestagung.gamm-ev.de/wp-content/uploads/2023/05/20230517_BookofAbstracts_final_red.pdf SP - 363 EP - 364 PB - GAMM e.V. CY - Dresden ER - TY - GEN A1 - Tsai, Pei-Yun A1 - Schmidt, Heiko A1 - Klein, Marten T1 - Effects of Reynolds number on turbulent concentric coaxial pipe flow using stochastic modeling T2 - Book of Abstracts of the 93rd Annual Meeting of the International Association of Applied Mathematics and Mechanics KW - spanwise wall curvature KW - turbulent pipe flow KW - stochastic modeling KW - boundary layer theory KW - one-dimensional turbulence Y1 - 2023 UR - https://jahrestagung.gamm-ev.de/wp-content/uploads/2023/05/20230517_BookofAbstracts_final_red.pdf SP - 365 PB - GAMM e.V. CY - Dresden ER - TY - GEN A1 - Klein, Marten T1 - Map-based stochastic modeling of multiscale transfer processes in turbulent flows T2 - Book of Abstracts of the 93rd Annual Meeting of the International Association of Applied Mathematics and Mechanics N2 - The detailed modeling of turbulent mixing has remained a numerical challenge for a number of applications, ranging from chemically reacting flows to noise prediction in technical flows, and encompassing convection on multiple scales in the geophysical context, among others. Complications arise from the dynamical complexity of turbulence that manifests itself by emergent small-scale flow features, scaling cascades, and intermittency due to prescribed forcings, boundary and initial conditions. In order to robustly predict, for example, the occurrence of catalytic reactions, generation of mixing noise, or the heat transfer across a layer of fluid, it is crucial to represent the physical redistribution processes in the flow with a proper account of participating time and length scales. This yields scale-locality and causality constraints that can usually only be fully addressed by direct numerical simulation (DNS) based on the discretized three-dimensional (3-D) Navier-Stokes equations, which is a very costly undertaking and limited to moderate or low turbulence intensities. In order to over- come the fundamental limitations of statistical turbulence models and numerical cost of DNS, so-called map-based stochastic turbulence models have been developed and increasingly applied to various mutiphysical flows over the last couple of decades. These models utilize onedimensional (1-D) generalized Baker’s maps in order to distinguish advective filamentation from molecular diffusion processes, resolving all relevant scales of the flow along a single physical coordinate. Baker’s maps are probabilistically sampled with respect to size, location, and time of occurrence which introduces dynamical complexity into the bottom-up modeling approach. When the sampling is based on the evolving flow state, a self-contained reduced- order model with predictive capabilities for turbulent flows can be formulated. In the talk, I will summarize the map-based stochastic modeling strategy with an emphasize on the so-called One-Dimensional Turbulence (ODT) model. After that, I will discuss some recent advances in the field, demonstrating the applicability of the approach across flow configurations. I will address in more detail the flow physics representation by means of entrainment and passive scalar mixing in turbulent jets, as well as heat flux and wall shear stress fluctuations in heated channels and stably-stratified atmospheric boundary layers. KW - stochastic modeling KW - one-dimensional turbulence KW - heat and mass transfer KW - boundary layer KW - turbulent mixing Y1 - 2023 UR - https://jahrestagung.gamm-ev.de/wp-content/uploads/2023/05/20230517_BookofAbstracts_final_red.pdf SP - 362 PB - GAMM e.V. CY - Dresden ER - TY - GEN A1 - Glawe, Christoph A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Stochastic deconvolution of wall statistics in Reynolds-averaged Navier–Stokes simulations based on one-dimensional turbulence T2 - Proceedings in applied mathematics and mechanics : PAMM N2 - Reynolds-averaged Navier–Stokes simulation (RaNS) is state-of-the-art for numerical analysis of complex flows at high Reynolds number. Standalone RaNS may yield a reasonable estimate of the wall-shear stress and turbulent drag if a proper wall-function is prescribed, but detailed turbulence statistics cannot be obtained, especially at the wall. This lack in modeling is addressed here by a stochastic deconvolution strategy based on a stochastic one-dimensional turbulence (ODT) model. Here, a one-way coupling strategy is proposed in which a forcing term is computed from the balanced RaNS solution that is in turn utilized in the ODT model. The temporally developing ODT solution exhibits turbulent perturbations but relaxes toward the local RaNS solution due to resolved molecular-diffusive processes. It is demonstrated that the approach is able to recover the distribution of positive wall-shear stress fluctuations in turbulent channel flow. When formulated as post-processing tool, it is suggested that RaNS can be enhanced by ODT providing economical means for local high-fidelity numerical modeling based on a low-fidelity flow solution. KW - stochastic deconvolution KW - Reynolds-averaged Navier-Stokes simulation (RANS) KW - turbulent channel flow KW - turbulent boundary layer KW - one-dimensional turbulence Y1 - 2023 U6 - https://doi.org/10.1002/pamm.202300055 SN - 1617-7061 VL - 23 IS - 3 ER - TY - GEN A1 - Medina Méndez, Juan Ali A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Investigating dissipative roughness effects on turbulent drag using a stochastic turbulence model T2 - 18th European Turbulence Conference (ETC18), 4-6 September 2023, Valencia Y1 - 2023 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Medina_2023_Abstract_ETC18_Roughness.pdf CY - Valencia ER - TY - GEN A1 - Medina Méndez, Juan Ali A1 - Sharma, Sparsh A1 - Schmidt, Heiko A1 - Klein, Marten T1 - Toward the use of a reduced-order and stochastic turbulence model for assessment of far-field sound radiation: Low Mach number jet flows T2 - Proceedings in Applied Mathematics and Mechanics Y1 - 2023 U6 - https://doi.org/10.1002/pamm.202300186 SN - 1617-7061 VL - 23 IS - 3 ER - TY - GEN A1 - Klein, Marten A1 - Kessler, Robert William A1 - Schmidt, Heiko T1 - On the influence of a wavy leading edge on the aerodynamic drag of a wing: A numerical parameter study T2 - STAB Jahresbericht 2023 KW - airfoil aerodynamics KW - passive flow control KW - CFD (RANS, LES) KW - wavy leading edge Y1 - 2023 UR - https://www.dlr.de/as/Portaldata/5/Resources/dokumente/veranstaltungen/stab_workshop/Jahresbericht2023.pdf UR - https://www.dlr.de/as/desktopdefault.aspx/tabid-128/268_read-1678/ VL - 21/2023 SP - 110 EP - 111 PB - Deutsche Strömungsmechanische Arbeitsgemeinschaft (STAB) CY - Göttingen, Germany ER - TY - GEN A1 - Tsai, Pei-Yun A1 - Schmidt, Heiko A1 - Klein, Marten T1 - Investigating heat transfer properties of tubular heat exchangers with a stochastic turbulence model T2 - 1st EIZ (Energie-Innovationszentrum) Annual Meeting, 24-25 April 2024, Cottbus, Germany Y1 - 2024 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Tsai_2024_EIZ1_abstract.pdf CY - Cottbus, Germany ER - TY - GEN A1 - Tsai, Pei-Yun A1 - Schmidt, Heiko A1 - Klein, Marten T1 - Features of turbulent boundary layers in heated concentric coaxial pipe flow at high Reynolds and low Prandtl numbers T2 - ICTAM 2024 Y1 - 2024 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Tsai_2024_poster_ICTAM2024.pdf UR - https://www.ictam2024.org/view.php?ACT=view&key=42 U6 - https://doi.org/10.13140/RG.2.2.30075.12323 CY - Daegu, South Korea ER - TY - GEN A1 - Tsai, Pei-Yun A1 - Schmidt, Heiko A1 - Klein, Marten T1 - Investigating Prandtl number effects in heated concentric coaxial pipe flow at high Reynolds number T2 - 1st European Fluid Dynamics Conference (EFDC1), 16-20 September 2024, Aachen, Germany Y1 - 2024 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Tsai_2024_EFDC1_abstract.pdf UR - https://www.aia.rwth-aachen.de/fileadmin/user_upload/Daily_Scientific_Program.pdf CY - Aachen, Germany ER - TY - GEN A1 - Tsai, Pei-Yun A1 - Schmidt, Heiko A1 - Klein, Marten T1 - Theoretical analysis and stochastic modeling of turbulent heat transfer in annular pipe flows T2 - 77th Annual Meeting of the Division of Fluid Dynamics, November 24–26, 2024; Salt Lake City, Utah N2 - Heat transfer in annular pipes is determined by the thermal and momentum boundary layer at the cylindrical inner and outer walls, respectively. The relative contributions are expressed by a local Nusselt number that depends on the radius ratio, the Prandtl number, and the Reynolds number. Direct numerical simulation (DNS) has been used previously to infer closure relations constrained to weakly turbulent flow due to numerical resource requirements. Here, stochastic one-dimensional turbulence (ODT) is utilized as a standalone tool as an alternative to DNS. ODT offers full-scale resolution along a representative radial domain, providing predictive capabilities relative to a calibrated reference case at a radically reduced cost. On average, ODT obeys radial balance equations compatible with the Navier-Stokes equations. Separating the boundary layer into a diffusion and a mixing-length dominated region in cylindrical geometry yields wall-curvature corrections at the inner wall. The proposed expressions can be used to enhance prescribed wall functions, for example, in Reynolds-averaged Navier-Stokes simulations. KW - heat transfer KW - boundary layer theory KW - stochastic modeling KW - one-dimensional turbulence KW - spanwise wall curvature KW - heated pipe flow Y1 - 2024 UR - https://meetings.aps.org/Meeting/DFD24/Session/T40.7 PB - American Physical Society ER - TY - GEN A1 - Klein, Marten A1 - Zenker, Christian A1 - Starick, Tommy A1 - Schmidt, Heiko T1 - Stochastic modeling of multi-stream mixing based on one-dimensional turbulence T2 - 77th Annual Meeting of the Division of Fluid Dynamics N2 - Measurements of multiple scalar mixing in a turbulent jet show a strong location dependence of the scalar fluctuations and mixing processes. Mixing is quantitatively described by the state space of scalar fluctuations in terms of a joint probability density function (JPDF). The JPDF evolves in the downstream and radial directions and has non-Gaussian shape which is a burden for mixing modeling since factoring into marginal distribution functions is not permissible. Stochastic simulations based on one-dimensional turbulence (ODT) are able to reasonably reproduce the JPDF and its spatial evolution by a parabolic marching problem that circumvents constraints of the underlying elliptic problem. The model reproduces the inertial-advective range (exponent -5/3) and predicts the emergence of the viscous-advective range (exponent -1) at higher wavenumbers as the Schmidt number increases. The model offers full-scale resolution at affordable cost providing means to reasonably capture state-space statistics of turbulent mixing. KW - turbulent mixing KW - one-dimensional turbulence KW - coaxial jet KW - multi-stream mixing Y1 - 2024 UR - https://meetings.aps.org/Meeting/DFD24/Session/ZC40.4 PB - American Physical Society ER - TY - GEN A1 - Klein, Marten A1 - Medina Méndez, Juan Alí A1 - Schöps, Mark Simon A1 - Schmidt, Heiko A1 - Glawe, Christoph T1 - Towards physics-based nowcasting of the instantaneous wind velocity profile using a stochastic modeling approach T2 - STAB Jahresbericht 2024 zum 24. DGLR-Fachsymposium der STAB, 13. - 14. November 2024, Regensburg N2 - The primary objective of this contribution is to provide an overview of the regime-spanning forward modeling capabilities offered by the stochastic one-dimensional turbulence model. The focus is on the applicability of the model and its validation for neutral and stable atmospheric boundary layer flows as a prerequisite for future applications to challenging atmospheric conditions. KW - atmospheric boundary layer KW - stochastic modeling KW - one-dimensional turbulence KW - wind energy KW - wind shear and veer Y1 - 2024 UR - https://bfm.rcbe.de/files/2024/11/2024_STAB-Jahresbericht.pdf SP - 162 EP - 163 PB - Deutsche Strömungsmechanische Arbeitsgemeinschaft, STAB CY - Regensburg [et al.] ER - TY - GEN A1 - Vallem, Rishindra A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Capabilities and limitations of smoothed particle hydrodynamics for the simulation of two‐phase flow instabilities T2 - Proceedings in Applied Mathematics and Mechanics N2 - Smoothed particle hydrodynamics (SPH) is a mesh‐free, Lagrangian particle‐based method that is able to simulate multiphase flows in an economical manner. However, its ability to capture the flow regimes and regime transitions in two phase (liquid‐gas) internal flows, such as pipe or channel flows is not yet generally established. To address this lack in understanding, we first examine a laminar rising bubble case in order to evaluate the fluid‐fluid interface representation and transient interface evolution by the solver. With a focus towards the transition mechanism from a stratified flow regime to a slug flow regime, we investigate the Kelvin–Helmholtz instability (KHI) both qualitatively and quantitatively, initially focusing on a low density ratio () and then extending it to a high density ratio (). For the low density ratio, we conduct an analysis of the temporal evolution and demonstrate that the SPH solver captures the initial exponential growth in qualitative agreement with inviscid linear stability theory (LST) and reference numerical data for shear‐dominated flow with Richardson number . By conducting eight additional simulations for various for the high density ratio, we demonstrate that the numerically obtained parameter value for instability is around , which is in reasonable agreement with the theoretically expected value of . Based on the SPH results obtained for the range , we suggest a simple parameterization of the reduction of the effective growth rate proportional to . KW - Smoothed Particle Hydrodynamics KW - two-phase flow KW - Kelvin-Helmholtz instability KW - rising bubble KW - growth rate Y1 - 2024 U6 - https://doi.org/10.1002/pamm.202400206 SN - 1617-7061 VL - 24/2024 PB - Wiley CY - Weinheim ER - TY - GEN A1 - Klein, Marten A1 - Kessler, Robert William A1 - Schmidt, Heiko T1 - Numerical investigation of drag reduction effects on a track bicycle fork using wings with a wavy leading edge T2 - Proceedings in Applied Mathematics and Mechanics N2 - Reynolds‐averaged Navier–Stokes (RANS) and large‐eddy simulations (LES) of the flow around wings with a wavy leading edge (WLE) are conducted in order to assess the capabilities of a passive flow control strategy for drag reduction. The intended application is indoor track cycling with controlled flow conditions. A section of a single fork rod is investigated in order to make the numerical simulations feasible. The present study reveals that net drag reduction is possible by a nonsinusoidal modification of the leading edge of the wing. However, the drag reduction effect remains limited to a few percent. While RANS and LES yield the same drag coefficient for a reference case, RANS underestimates the drag reduction effect for a longer wing and the WLE cases, but exhibits otherwise a qualitatively similar trend as the LES. With the aid of RANS, an optimal geometry is obtained defined by the wavelength‐to‐chord length ratio of and the amplitude‐to‐chord length ratio of . Corresponding LES results give an indication of the origin of drag reduction by a hampered vortex shedding. The generation of smaller and more streamwise oriented vortical flow structures at the trailing edge and behind the WLE wing is correlated with significantly reduced lift fluctuations and drag reduction. KW - sports aerodynamics KW - passive flow control KW - aerodynamic drag KW - drag reduction KW - computational fluid dynamics KW - turbulence modeling Y1 - 2024 U6 - https://doi.org/10.1002/pamm.202400178 SN - 1617-7061 VL - 24 SP - 1 EP - 14 PB - Wiley ER - TY - GEN A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Capturing features of transient boundary layers with a map-based stochastic modeling approach N2 - Atmospheric boundary layers (ABLs) exhibit transient processes on various time and length scales, with a scale separation between the large-scale forcing and the small-scale response. Some crucial but standing challenges in modeling and simulation of ABL flows lie in the detailed representation of boundary layer turbulence (e.g. [1]). This includes intermittent and transient processes and the resulting turbulent and laminar response mechanisms. State-of-the-art subgrid-scale models utilize statistical closures for an averaged resolved flow state on the basis of the Monin-Obhukov similarity theory (MOST) to represent scalar fluxes and momentum fluxes (e.g. [2]). Fluctuations are not resolved in MOST. Instead, their ensemble effect is parameterized by the resolved large scales, neglecting backscatter from the unresolved small scales. Data-driven stochastic approaches aim to incorporate fluctuations and the spontaneous occurrence of instabilities, but at the expense of ad hoc forcings (e.g. [3]). The mentioned limitations can be removed by a physically compatible representation of turbulent fluctuations. This is addressed here by utilization of a map-based stochastic approach that is based on the one-dimensional turbulence (ODT) model [4]. ODT autonomously evolves vertical flow profiles for prescribed initial and boundary conditions, and physical forcings. The model captures turbulent cascade phenomenology and aims to resolve all relevant turbulent scales along a physical coordinate. Turbulent advection is modeled by a stochastically sampled sequence of spatial mapping events that punctuate the deterministic advancement due to viscous and Coriolis forces. The offered dynamical complexity removes the need for artificial forcings. In the contribution, key results from recent and ongoing studies related to the reduced-order modeling of ABL flows will be presented. First, surface scalar and momentum fluxes in turbulent channels are discussed emphasizing the correctly predicted inapplicability of the Reynolds analogy [5]. Second, the influence of system rotation and stratification is discussed for low-order velocity statistics and the participating turbulent scales [6,7]. Third, results for nonequilibrium conditions are presented for a transient ABL that exhibits turbulent bursts in response to an oscillatory geostrophic forcing [8]. Last, some preliminary results on the stochastic deconvolution of averaged data [9] will be presented focusing on the additional physical insight that is offered by the model. References [1] L. Mahrt. Annu. Rev. Fluid Mech. 46:23–45, 2014. [2] I. Stiperski, and M. Calaf. Phys. Rev. Lett. 130:124001, 2023. [3] V. Boyko, and N. Vercauteren. Q. J. R. Meteorol. Soc. 149(755):2125–2145, 2023. [4] A. R. Kerstein, and S. Wunsch. Bound.-Lay. Meteorol. 118:325–356, 2006. [5] M. Klein, H. Schmidt, and D. Lignell. Int. J. Heat Fluid Flow 93:108889, 2022. [6] M. Klein, and H. Schmidt. Adv. Sci. Res. 19:117–136, 2022. [7] L. S. Freire. Bound.-Lay. Meteorol. 184:25–43, 2022. [8] M. Klein, and H. Schmidt. Adv. Sci. Res. 20:55–64, 2023. [9] C. Glawe, M. Klein, and H. Schmidt. Proc. Appl. Math. Mech. 23:e202300055, 202 KW - atmospheric boundary layer KW - stochastic modeling KW - one-dimensional turbulence KW - transient effects Y1 - 2024 U6 - https://doi.org/10.5194/egusphere-egu24-15560 PB - Copernicus GmbH ER - TY - GEN A1 - Klein, Marten A1 - Medina Méndez, Juan Alí A1 - Schmidt, Heiko T1 - Resolving the electrostatic boundary layer in a turbulent electrohydrodynamic flow with a map-based stochastic modeling approach T2 - 1st European Fluid Dynamics Conference - Daily Scientific Program N2 - Electrohydrodynamically (EHD) enhanced wall-bounded turbulent flows are encountered in various technical applications ranging from air-cleaning devices (like precipitators) to electrolyte flows (like redox flow batteries). The multi-physical processes governing the flow properties, however, are not yet very well understood. This is due the inaccessibility to and limitations of measurement equipment and numerical resolution requirements imposed by the electrostatic charge boundary layer that interacts on different time scales with the turbulent boundary layer. Recent advances in measurement techniques allow to resolve the exponential electrostatic charge boundary layer in a charged particle-ladden, weakly turbulent gas flow [1], which is qualitatively compatible with direct numerical simulation (DNS) results for a weakly turbulent flow of an electrolyte [2] at low Reynolds (Re) number. The challenge that remains is the extrapolation to highly turbulent flow conditions. Charged particles are heavy compared with fluid molecules and can be treated as a high Schmidt (Sc) number scalar, which is a burden for DNS. In this contribution, it is demonstrated that this burden can be overcome for the transient boundary layer evolution by utilizing a radically reduced, map-based stochastic one-dimensional turbulence (ODT) model. The model predicts a significant enhancement of the skin friction drag due to turbulence-induced screening layer depletion [3], as summarized in Fig. 1. In the talk, features of the instantaneous and mean velocity and electrostatic boundary layer will be presented. The plausibility of the model prediction is evaluated on a physical basis, encompassing details of the model formulation and the emerging hydrodynamic and electrokinetic properties of the boundary layer. References [1] W. Xu, S. Jantaˇc, T. Matsuyama, and H. Grosshans. arXiv:2306.06970, 2023. (Accepted for publication by Exp. Fluids.) [2] R. Ostilla-M´onico, and A. A. Lee. Faraday Discuss., 199:159–173, 2017. [3] M. Klein, J. A. Medina M´endez, and H. Schmidt. Tech. Mech., 43:111–127, 2023. KW - EHD turbulence KW - electric double layer KW - boundary layer KW - Schmidt number effects KW - one-dimensional turbulence KW - stochastic modeling KW - skin friction drag Y1 - 2024 UR - https://www.conftool.org/efdc1/index.php?page=browseSessions&presentations=show&search=822+klein UR - https://www.aia.rwth-aachen.de/fileadmin/user_upload/Daily_Scientific_Program.pdf CY - Aachen ER - TY - GEN A1 - Parekh, Parshva Atulbhai A1 - Gschwander, Stefan A1 - Klein, Marten A1 - Gamisch, Sebastian T1 - CFD-based analysis and minimization of mixing during the charging phase of a thermal energy storage tank T2 - 1. Jahresfachtagung des Energie-Innovationszentrums (EIZ) Cottbus N2 - Transient numerical simulations are performed for a cuboidal storage tank in order to resolve the transient features of the charging phase in a feasible manner. A diffuser is utilized for the inflow of water in order avoid large-scale overturning fluid motions in order to establish a thermal stratification. It is demonstrated that the thermal stratification can be furrther enhanced by introducing a layer of a porous medium at the top of the storage tank based on computational fluid dynamics (CFD) simulations using COMSOL Multiphysics®. Initially, a storage tank configuration without a porous medium is simulated in order to establish a baseline understanding. Subsequent simulations are performed systematically varying various parameters of the porous medium, such as porosity, location, and inclination. The inclined placement of the porous sheet yields a reduction of the thermocline thickness by approximately 38% compared to the reference case, thereby significantly enhancing the thermal stratification. As next step, the results obtained will be verified in an experimental apparatus at Fraunhofer ISE. In the talk, the set-up of the numerical model, including the treatment of the porous sheet, the thermocline evolution together with the governing fluid flow, and the effect of an additionally installed porous sheet will be discussed KW - thermal energy storage tank KW - mixing KW - porous media KW - computational fluid dynamics Y1 - 2024 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Klein_2024_EIZ1_abstract.pdf CY - Cottbus ER - TY - GEN A1 - Polasanapalli, Sai Ravi Gupta A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Investigation of the impact of transient pressure gradients on turbulent channel flow dynamics T2 - Proceedings in Applied Mathematics and Mechanics N2 - The effect of transient pressure gradients, or transient pumping in turbulent channel flow configuration, is investigated. Employing a cost-efficient reduced-order stochastic method known as one-dimensional turbulence (ODT) modeling, simulations explore different signal shapes for the modulation of the prescribed pressure gradient forcing, including sinusoidal modulation, step-like modulation, and piecewise sinusoidal beating. Various cycle periods and active pumping times are investigated. The simulations are conducted at a frictional Reynolds number of $Re_\tau = 395$ and a molecular Prandtl number of $Pr = 1$. The study adopts a passive scalar formulation to investigate heat transfer properties. The study quantifies the effects of transient pressure gradients on heat transfer rate, drag, and pumping power. Preliminary ODT predictions suggest that all transient cases exhibit lower heat transfer rates and a higher pumping power requirement than the constant pressure gradient case, with the step-like modulation yields superior skin-friction drag and heat transfer rate reductions relative to other signals. KW - turbulent heat transfer KW - turbulent drag KW - pumping power KW - one-dimensional turbulence KW - pulsating flow Y1 - 2024 U6 - https://doi.org/10.1002/pamm.202400183 SN - 1617-7061 VL - 24 SP - 1 EP - 12 PB - Wiley-VCH GmbH CY - Weinheim ER - TY - GEN A1 - Polasanapalli, Sai Ravi Gupta A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Investigating modifications of the heat transfer by velocity boundary conditions in turbulent thermal convection using an off-lattice Boltzmann method T2 - STAB Jahresbericht 2024 N2 - In our contribution to the STAB workshop, we will present the effect of different surfaces on flow and heat transfer characteristics, taking into account the no-slip, free-slip, and finite-slip lengths of the walls. Following that, the impact of different walls, such as horizontal or side walls, will be discussed separately. Finally, the influence of finite slip length on turbulent characteristics will also be addressed. The work was supported by the North- German Supercomputing Alliance (HLRN) and numerical simulations were carried out on HLRN high-performance computing facilities at Berlin and Göttingen (project ID: bbi00022). KW - lattice Boltzmann method KW - thermal convection KW - hydrophilic and hydrophobic surfaces KW - Navier slip boundary condition Y1 - 2024 UR - https://bfm.rcbe.de/files/2024/11/2024_STAB-Jahresbericht.pdf SP - 40 EP - 41 PB - Deutsche Strömungsmechanische Arbeitsgemeinschaft, STAB CY - Regensburg [et al.] ER - TY - CHAP A1 - Klein, Marten A1 - Tsai, Pei-Yun A1 - Schmidt, Heiko ED - Dillmann, Andreas ED - Heller, Gerd ED - Krämer, Ewald ED - Wagner, Claus ED - Weiss, Julien T1 - Stochastic Modeling and Large-Eddy Simulation of Heated Concentric Coaxial Pipes T2 - New Results in Numerical and Experimental Fluid Mechanics XIV, STAB/DGLR Symposium 2022 N2 - Turbulent concentric coaxial pipe flows are numerically investigated as canonical problem addressing spanwise curvature effects on heat and momentum transfer that are encountered in various engineering applications. It is demonstrated that the wall-adapting local eddy-viscosity (WALE) model within a large-eddy simulation (LES) framework, without model parameter recalibration, has limited predictive capabilities as signalized by poor representation of wall curvature effects and notable grid dependence. The identified lack in the modeling of radial transport processes is therefore addressed here by utilizing a stochastic one-dimensional turbulence (ODT) model. A standalone ODT formulation for cylindrical geometry is used in order to assess to which extent the predictability can be expected to improve by utilizing an advanced wall-modeling strategy. KW - Heat and mass transfer KW - Stochastic turbulence modeling KW - Spanwise curvature effects KW - Pipe flow Y1 - 2024 SN - 978-3-031-40482-5 SN - 978-3-031-40481-8 U6 - https://doi.org/10.1007/978-3-031-40482-5_41 SN - 1612-2909 SN - 1860-0824 N1 - This research is supported by the German Federal Government, the Federal Ministry of Education and Research and the State of Brandenburg within the framework of the joint project EIZ: Energy Innovation Center (project numbers 85056897 and 03SF0693A) with funds from the Structural Development Act (Strukturstärkungsgesetz) for coal-mining regions. M.K. acknowledges support by the BTU Graduate Research School (Conference Travel Grant). SP - 435 EP - 444 PB - Springer CY - Cham ER - TY - GEN A1 - Klein, Marten T1 - Map-based stochastic simulation data of a transient Ekman boundary layer N2 - A journal paper in Advances in Science and Research details the numerical modeling approach used to create the data. Here, the model input files, the raw data, processed data, and plot scripts are provided that support the research. The code used to generate the data is an extended version of the one-dimensional turbulence (ODT) model. The current model implementation utilizes an adaptive grid that further increases numerical efficiency. A reduced version of the adaptive ODT code used in this work is available free of charge at: https://github.com/BYUignite/ODT The bash script makePlot.sh is the top-level driver and contains all additional information about the cases. Some other Details are provided by low-level README files. Python-3.8 is required to run the scripts. KW - atmospheric turbulence KW - boundary layer theory KW - multiscale flow KW - reduced-order stochastic modeling Y1 - 2023 ER - TY - GEN A1 - Polasanapalli, Sai Ravi Gupta A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Towards stochastic subgrid-scale modeling of turbulent thermal convection in an under-resolved off-lattice Boltzmann method T2 - Proceedings in applied mathematics and mechanics : PAMM N2 - A characteristic-based Off-Lattice Boltzmann Method (OLBM) and a stochastic One-Dimensional Turbulence (ODT) model is utilized for numerical simulation of turbulent thermal convection. Standalone ODT results for low-order statistics are compared with those from various eddy-viscosity-based subgrid-scale models utilized in Large-Eddy Simulations (LES) with OLBM. The predictive capabilities of both approaches are discussed by comparison with available reference Direct Numerical Simulation (DNS) results. All turbulence models are able to predicted the mean temperature, but fail to fully capture fluctuations. While the OLBM aims to represent large-scale structures, it misses some constitutional small-scale fluctuations. By contrast, the reduced-order ODT model captures small-scale fluctuations in the vicinity of the wall, but cannot resolve the organized bulk flow. Here, the modeling capabilities of both OLBM and ODT as standalone tools are discussed. On this basis, a strategy for the incorporation of ODT as wall model in OLBM is suggested. KW - thermal convection KW - heat transfer KW - lattice Boltzmann method KW - turbulence modeling KW - one-dimensional turbulence Y1 - 2023 UR - https://onlinelibrary.wiley.com/doi/10.1002/pamm.202300223 U6 - https://doi.org/10.1002/pamm.202300223 SN - 1617-7061 SP - 1 EP - 9 ER - TY - GEN A1 - Klein, Marten A1 - Zenker, Christian A1 - Starick, Tommy A1 - Schmidt, Heiko T1 - Stochastic modeling of multiple scalar mixing in a three-stream concentric coaxial jet based on one-dimensional turbulence T2 - International Journal of Heat and Fluid Flow N2 - Modeling turbulent mixing is a standing challenge for nonpremixed chemically reacting flows. Key complications arise from the requirement to capture all relevant scales of the flow and the necessity to distinguish between turbulent advective transport and molecular diffusive transport processes. In addition, anisotropic mean shear, variable advection time scales, and the coexistence of turbulent and nonturbulent regions need to be represented. The fundamental issues at stake are addressed by investigating multi-scalar mixing in a three-stream coaxial jet with a map-based stochastic one-dimensional turbulence model. ODT provides full-scale resolution at affordable costs by a radical reduction of complexity compared to high-fidelity Navier–Stokes solvers. The approach is partly justified by an application of the boundary-layer approximation, but neglects fluctuating axial pressure gradients. It is demonstrated that low-order scalar statistics are reasonably but not fully captured. Despite this shortcoming, it is shown that the model is able to reproduce experimental state-space statistics of multi-stream multi-scalar mixing. The model therefore offers physics-compatible improvements in multi-stream mixing modeling despite some fundamental limitations that remain from unjustified assumptions. KW - map-based stochastic advection modeling KW - multiple passive scalars KW - one-dimensional turbulence KW - turbulent jet KW - turbulent mixing Y1 - 2023 U6 - https://doi.org/10.1016/j.ijheatfluidflow.2023.109235 SN - 0142-727X N1 - This article is part of the "TSFP12 Special Issue". VL - 104 SP - 1 EP - 17 ER - TY - GEN A1 - Tsai, Pei-Yun A1 - Schmidt, Heiko A1 - Klein, Marten T1 - Investigating Reynolds number effects in turbulent concentric coaxial pipe flow using stochastic one-dimensional turbulence modeling T2 - Proceedings in Applied Mathematics and Mechanics N2 - The present study numerically investigates turbulent momentum transfer in concentric coaxial (annular) pipe flow with small radius ratios (𝜂 = 𝑅𝑖∕𝑅𝑜 = 0.1,0.04,0.02). To model the flow, a stochastic one-dimensional turbulence (ODT) model formulated for cylindrical geometry is used that provides full-scale resolution along a representative radial coordinate. The present investigation extends the model validation by Tsai et al. (PAMM,22:e202200272, 2023), to radius ratios smaller than 0.1 and addresses boundary layers with strong span-wise curvature effects. The focus is on the assessment and analysis of statistical flow features in the vicinity of the inner cylinder wall, particularly in cases with small radius ratios. Following Boersma & Breugem (Flow Turbul. Com-bust.,86:113–127, 2011), classical boundary-layer and mixing-length theory is utilized to analyze the model predictions. The results demonstrate that the ODT model captures leading-order curvature and mixing-length effects by its physics-compatible construction. Utilizing the model for extrapolation to high Reynolds numbers inaccessible to conventional high-fidelity numerical approaches shows that curvature effects persist and nonlocally affect the entire boundary layer. The model results provide support for a spanwise-curvature-modified wall function. KW - turbulent coaxial pipe flow KW - stochastic modeling KW - one-dimensional turbulence KW - spanwise curvature KW - turbulent boundary layer KW - high Reynolds number Y1 - 2023 U6 - https://doi.org/10.1002/pamm.202300167 SN - 1617-7061 N1 - Proceedings of the GAMM Annual Meeting 2023, Dresden, Germany VL - 23 IS - 4 SP - 1 EP - 8 ER - TY - GEN A1 - Klein, Marten A1 - Starick, Tommy A1 - Zenker, Christian A1 - Medina Méndez, Juan Alí A1 - Schmidt, Heiko T1 - Reduced order stochastic modeling of turbulent mixing based on conservative baker’s maps T2 - Proceedings of the 14th International ERCOFTAC Symposium on Engineering Turbulence Modelling and Measurements (ETMM-14) N2 - The detailed numerical representation of turbulent mixing processes is a standing challenge for non-premixed chemically reacting flows. The full range of relevant flow scales needs to be captured and it is also necessary to distinguish turbulent advective from molecular diffusive processes in order to represent Reynolds and Schmidt number effects. These requirements are addressed here by utilizing two different map-based stochastic turbulence modeling strategies. The one-dimensional turbulence (ODT) model utilizes event-based turbulence modeling, whereas the hierarchical parcel-swapping (HiPS) model is a fully event-based mixing model. ODT provides full-scale resolution at affordable costs by dimensional model reduction based on the boundary-layer approximation to shear flow. HiPS is far less costly than ODT but currently limited to locally homogeneous isotropic turbulence. The physics-compatible modeling capabilities with respect to phase-space representation of turbulent mixing are demonstrated for two canonical cases using standalone model formulations. KW - turbulent mixing KW - one-dimensional turbulence (ODT) KW - hierarchical parcel swapping (HiPS) KW - stochastic turbulence modeling KW - round jet KW - passive scalar Y1 - 2023 UR - https://etmm.ercoftac.org/etmm/program/conference-program/ UR - https://drive.google.com/file/d/1q2BDOO5bXfqq0Y4z4HCGndiFI033bPyg/view?usp=drive_link SP - 613 EP - 618 PB - ERCOFTAC CY - Barcelona, Spain ER - TY - GEN A1 - Vallem, Rishindra A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Numerical modeling and simulation of two-phase internal flow instabilities using Smoothed Particle Hydrodynamics (SPH) T2 - STAB Jahresbericht 2023 KW - Smoothed Particle Hydrodynamics (SPH) KW - Kelvin-Helmholtz instability KW - linear stability analysis KW - two-phase flow Y1 - 2023 UR - https://www.dlr.de/as/Portaldata/5/Resources/dokumente/veranstaltungen/stab_workshop/Jahresbericht2023.pdf UR - https://www.dlr.de/as/desktopdefault.aspx/tabid-128/268_read-1678/ VL - 21/2023 SP - 158 EP - 159 PB - Deutsche Strömungsmechanische Arbeitsgemeinschaft (STAB) CY - Göttingen, Germany ER - TY - GEN A1 - Tsai, Pei-Yun A1 - Schmidt, Heiko A1 - Klein, Marten T1 - Stochastic modeling of asymmetric turbulent boundary layers in annular pipe flow Y1 - 2023 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Tsai_2023_poster_PragueSummerSchoolX.pdf U6 - https://doi.org/10.13140/RG.2.2.18789.78567 N1 - Stochastics in Fluids Summer School and Workshop 2023, Czech Academy of Sciences Institute of Mathematics, Prague, Czech Republic ER - TY - GEN A1 - Klein, Marten A1 - Medina Méndez, Juan Alí A1 - Schmidt, Heiko T1 - Stochastic modeling of electrohydrodynamically enhanced drag in one-way and fully coupled turbulent Poiseuille and Couette flow T2 - Technische Mechanik N2 - Joint predictive modeling of hydrodynamics and electrokinetics is a standing numerical challenge but crucial for various applications in electrochemistry and power engineering. The present lack in modeling of electrohydrodynamic (EHD) turbulent flows lies in the treatment of small-scale processes and scale interactions. To overcome these limitations, a stochastic one-dimensional turbulence (ODT) model is utilized. The model aims to resolve all scales of the flow, but only on a notional line-of-sight, modeling turbulent advection by a stochastically sampled sequence of eddy events that punctuate deterministic molecular diffusive advancement. In this study, two canonical flow configurations are investigated that address different coupling strategies and flow physics. First, EHD effects in a variable-density vertical pipe flow of an ideal gas with an inner concentric electrode are investigated with a one-way coupled model formulation. Electric fields are generated by means of a corona discharge and the corresponding effect of a fixed ionic charge density field. Second, in order to reduce physical complexity, EHD effects the turbulent boundary layers in plane Couette flow of an isothermal univalent ionic liquid are investigated with a fully coupled model formulation. Both application cases demonstrate that ODT has predictive capabilities due to multiscale resolution of transport processes. Present results suggest that more expensive fully than one-way coupling of electrokinetics is crucial when charge relaxation times are significantly larger than the mean advection time scale. KW - turbulent drag enhancement KW - electrohydrodynamic turbulence KW - high Schmidt number KW - multiphysical boundary layers KW - one-dimensional turbulence Y1 - 2023 U6 - https://doi.org/10.24352/UB.OVGU-2023-049 SN - 0232-3869 N1 - This article is part of the "Special Issue for CMFF’22". VL - 43 IS - 1 SP - 111 EP - 127 ER - TY - GEN A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Capturing features of turbulent Ekman–Stokes boundary layers with a stochastic modeling approach T2 - Advances in Science and Research N2 - Atmospheric boundary layers (ABLs) exhibit transient processes on various time scales that range from a few days down to seconds, with a scale separation of the large-scale forcing and the small-scale turbulent response. One of the standing challenges in modeling and simulation of ABLs is a physically based representation of complex multiscale boundary layer dynamics. In this study, an idealized time-dependent ABL, the so-called Ekman–Stokes boundary layer (ESBL), is considered as a simple model for the near-surface flow in the mid latitudes and polar regions. The ESBL is driven by a prescribed temporal modulation of the bulk–surface velocity difference. A stochastic one-dimensional turbulence (ODT) model is applied to the ESBL as standalone tool that aims to resolve all relevant scales of the flow along a representative vertical coordinate. It is demonstrated by comparison with reference data that ODT is able to capture relevant features of the time-dependent boundary layer flow. The model predicts a parametric enhancement of the bulk–surface coupling in the event of a boundary layer resonance when the flow is forced with the local Coriolis frequency. The latter reproduces leading order effects of the critical latitudes. The model results suggest that the bulk flow decouples from the surface for high forcing frequencies due to a relative increase in detached residual turbulence. KW - turbulent boundary layer KW - stochastic modeling KW - periodic forcing KW - one-dimensional turbulence KW - rotating flow Y1 - 2023 UR - https://asr.copernicus.org/articles/20/55/2023/ U6 - https://doi.org/10.5194/asr-20-55-2023 SN - 1992-0636 SN - 1992-0628 N1 - This article is part of the special issue “EMS Annual Meeting: European Conference for Applied Meteorology and Climatology 2022”. N1 - This research is supported by the German Federal Government, the Federal Ministry of Education and Research and the State of Brandenburg within the framework of the joint project EIZ: Energy Innovation Center with funds from the Structural Development Act (Strukturstärkungsgesetz) for coal-mining regions. VL - 20 SP - 55 EP - 64 ER - TY - GEN A1 - Medina Méndez, Juan Ali A1 - Klein, Marten A1 - Schöps, Mark Simon A1 - Schmidt, Heiko T1 - Predicting volatile wind energy: Stochastic forward modeling and machine learning T2 - 86. Jahrestagung der DPG (86th Annual Conference of the DPG), DPG-Frühjahrstagung 2023, (DPG Spring Meeting 2023 of the Matter and Cosmos Section (SMuK), 20-24 March 2023, Technische Universität Dresden Y1 - 2023 UR - https://smuk23.dpg-tagungen.de/programm/assets/verhandlungen-smuk23.pdf UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Klein_poster_dpg23.pdf SN - 2751-0522 SP - S. 343 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - GEN A1 - Tsai, Pei‐Yun A1 - Schmidt, Heiko A1 - Klein, Marten T1 - Stochastic modeling and theoretical analysis of weakly heated concentric coaxial pipe flows at low prandtl number T2 - Proceedings in Applied Mathematics and Mechanics N2 - Heated concentric coaxial (annular) pipe flows are numerically investigated by a stochastic one‐dimensional turbulence (ODT) model. The main objective of this work is to more accurately predict the heat transfer in tubular heat exchangers at low Prandtl numbers by extending the analysis for weak temperature fluctuations as recently introduced in Tsai et al., Proceedings in Applied Mathematics and Mechanics, 23:e202300167, 2023. The ODT model offers the required predictive capabilities at affordable cost by providing full‐scale resolution of viscous, conductive, and turbulent advective transport processes along a representative radial coordinate. The Prandtl numbers and are considered for which the radius ratio of the annular pipe and the Reynolds number are varied. Numerical results demonstrate that the geometry (radius ratio) has a significant influence on the thermal boundary layer that emerges over the inner and outer curved wall, respectively. Application of boundary layer theory and mixing length arguments yield an analytical expression that includes both Reynolds number and curvature effects. Unknown closure coefficients are estimated with ODT, providing a physically based correlation for the Nusselt number. KW - Turbulent pipe flow KW - Coaxial heat exchanger KW - Low Prandtl number KW - Boundary layer theory KW - Mixing-length theory Y1 - 2025 U6 - https://doi.org/10.1002/pamm.70006 SN - 1617-7061 VL - 25 IS - 1 SP - 1 EP - 7 PB - Wiley CY - Weinheim ER - TY - GEN A1 - Marinković, Pavle A1 - Medina, Juan A. A1 - Schöps, Mark Simon A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Experiences from the bottom‐up development of an object‐oriented CFD solver with prospective hybrid turbulence model applications T2 - Proceedings in Applied Mathematics and Mechanics N2 - In this work, we discuss recent experiences related to the development and enhancement of a hybrid stochastic computational fluid dynamics (CFD) solver, the C++ version of the Implicit/Explicit (IMEX) time‐advancement algorithm used in the one‐dimensional turbulence‐based (ODT) large eddy simulation (LES) model, abbreviated as ODTLES. After being ported from Fortran 90, the current capabilities of the C++ code are restricted to the reproducibility of turbulent channel flow simulations with respect to the former Fortran code version that was able to achieve reasonable agreement with available reference direct numerical simulation (DNS) for low to moderate Reynolds number turbulent channel flows. This is far from satisfactory so that current efforts are centered on improving the solver code structure through comprehensive refactoring, robust unit testing, and strict adherence to code style guides, following the principles of Clean Code. We focus the discussion on a methodology to balance unit, regression, and integration testing, here for the LES component of the code. The objective is to frame a starting point that is relevant also for other CFD codes, irrespective of whether they utilize conventional or novel discretization or flow modeling approaches. KW - Computational fluid dynamics (CFD) KW - Solver development KW - Software maintainabilit KW - Software dependability KW - Large-eddy simulation (LES) KW - Stochastic subgrid scale modeling Y1 - 2025 U6 - https://doi.org/10.1002/pamm.202400190 SN - 1617-7061 VL - 25 IS - 1 PB - Wiley ER - TY - GEN A1 - Klein, Marten A1 - Medina Méndez, Juan Alí A1 - Schmidt, Heiko T1 - Simulating Volatile Wind Energy: Stochastic Forward Modeling and Machine Learning N2 - The transformation of the energy sector is based on the integration of various renewable sources, such as wind and solar energy. One of the key challenges for the integration of these sources into the existing power grid is their erratic and sometimes discontinuous availability (volatility). Wind energy is one of the most relevant sources of CO2 neutral electric energy, but volatile due to fluctuating wind fields on multiple scales. This has already been realized so that senors provide real-time information on the scale of individual wind turbines. However, fore- casting remains an unresolved problem since numerical weather prediction models cannot provide the necessary level of detail. New modeling strategies are required that integrate turbine-scale and meso-scale information for accurate site-specific short-term prediction. Present and forthcoming research aims to incorporate fluctuations on multiple levels of fidelity, depending on the abstraction layer KW - AI transfer KW - AI teaching KW - stochastic modeling KW - machine learning KW - wind energy KW - volatility modeling and prediction Y1 - 2022 UR - https://ai-science-atlas.innohub13.de/files/pdf/NSGSimulatingVolatileWindEnergyBTUpdf.pdf UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Klein_poster_KI-Atlas22.pdf PB - Innovation Hub 13, TH Wildau CY - Wildau ER - TY - GEN A1 - Li, Hanchen A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Simulation of radiatively driven mixing in a smoke cloud using "one-dimensional turbulence" N2 - Large-eddy simulations (LESs) are known to significantly overestimate entrainment in cloud-topped boundary layers, negatively impacting predictions on cloud mass and cover. This overestimation stems from coarse model resolutions that lead to numerical broadening of the entrainment layer. While it has been shown in direct numerical simulations (DNSs) that down-to-centimetre-scale resolutions can mitigate this issue, such high resolutions are not viable for most applications in the atmospheric sciences. The one-dimensional turbulence model (ODT), introduced by Kerstein [1], offers a computationally efficient alternative that provides full-scale resolution along a 1-D vertical domain. Molecular diffusion is explicitly resolved, while turbulent advection is modelled through a stochastically sampled sequence of spatial mappings, known as eddy events. Physically plausible eddy events are selected based on their current kinetic and potential energy. This allows an accurate representation of local turbulence properties and their dynamical complexity by evolving instantaneous property profiles. This study applies ODT to investigate cloud-top turbulent mixing processes driven by radiative cooling in a smoke cloud, benchmarking the results against DNS. Building on the preliminary findings by Meiselbach [2], we demonstrate improvements in mean profiles and turbulent fluxes of buoyancy and smoke concentration, showing ODT's ability to reproduce salient features observed in DNSs. In addition, we explore convective boundary layer scalings at extended Reynolds and Richardson numbers beyond those accessible in DNS studies. References: [1] A. R. Kerstein, Journal of Fluid Mechanics 392, 277334 (1999). [2] F. T. Meiselbach, Application of ODT to Turbulent Flow Problems, doctoral thesis, BTU Cottbus-Senftenberg (2015). Y1 - 2025 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Li_2025_poster_EGU.pdf U6 - https://doi.org/10.5194/egusphere-egu25-9491 ER - TY - GEN A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Investigating cutoff scales in turbulent Ekman flow with a map-based stochastic modeling approach N2 - The Ozmidov scale marks the cutoff scale above which overturning fluid motions in stably stratified shear flows are energetically prohibited. A recent study of a turbulent shear layer demonstrates that the Corrsin scale provides an intrinsic cutoff scale when stratification is absent [1]. For the neutral boundary layer, it is proposed by analogy to the mixing layer that the cutoff scale is linked to the Corrsin scale rather than the unbounded Ozmidov scale. The claim is numerically investigated for turbulent Ekman flow with the aid of Kerstein’s one-dimensional turbulence (ODT) model [2], utilizing the case setup described in [3]. ODT offers full-scale resolution along a vertical coordinate by autonomously evolving the instantaneous property profiles. Molecular diffusion is directly resolved, whereas turbulent advection is modeled by a stochastic process that is formulated with the aid of spatial mapping events, which are sampled based on the local available energy. In this model formulation, a cutoff scale is economically prescribed by limiting the sampling range of turbulent scales. Model results in terms of low-order and detailed turbulence statistics will be presented and compared to available reference data and theoretical analysis. References [1] F. G. Jacobitz and K. Schneider. Phys. Rev. Fluids 9:044602, 2024. [2] A. R. Kerstein and S. Wunsch. Bound.-Lay. Meteorol. 118:325–356, 2006. [3] M. Klein and H. Schmidt. Adv. Sci. Res. 19:117–136, 2022. Y1 - 2025 UR - https://presentations.copernicus.org/EGU25/EGU25-13495_presentation-h326475.pdf U6 - https://doi.org/10.5194/egusphere-egu25-13495 PB - Copernicus GmbH CY - Göttingen ER - TY - GEN A1 - Marinkovic, Pavle A1 - Medina, Juan A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Application of extended large-eddy simualtion (XLES) to turbulent channel flow T2 - Proceedings in applied mathematics and mechanics : PAMM N2 - Extended large-eddy simulation (XLES) offers a promising middle ground between computational efficiency and predictive accuracy in turbulent flow simulations. By integrating the one-dimensional turbulence model as a stochastic subgrid-scale approach, XLES autonomously resolves turbulent microscales in a dimensionally reduced setting. Our implementation employs a coarse grid solely for pressure calculations, while three specialized high-resolution grids handle the turbulence dynamics. This multi-scale architecture reduces computational requirements by approximately two orders of magnitude compared to direct numerical simulation while maintaining comparable accuracy. Our results for turbulent channel flow at Reynolds number 395 demonstrate that XLES with a base resolution of just cells closely matches DNS reference data, vastly outperforming implicit LES using identical resolution and discretization schemes. This updated implementation of XLES, though still under active development, demonstrates significant potential for accurately simulating wall-bounded turbulent flows while substantially reducing computational requirements compared to traditional high-fidelity approaches. Y1 - 2025 U6 - https://doi.org/10.1002/pamm.70010 SN - 1617-7061 VL - 25 : special issue : 95th Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM) IS - 2 SP - 1 EP - 7 PB - Wiley CY - Weinheim ER - TY - GEN A1 - Marinkovic, Pavle A1 - Medina Méndez, Juan A. A1 - Klein, Marten A1 - Schmidt, Heiko T1 - ODTLES : large-eddy simulation with autonomous stochastic subgrid-scale modeling applied to turbulent duct flow T2 - Proceedings of the Conference on Modelling Fluid Flow CMFF’25 N2 - In this work, we discuss the application of the One-Dimensional Turbulence-based (very) Large-Eddy Simulation model, abbreviated as ODTLES, to turbulent duct flow. ODTLES is a multi-scale flow model in which an autonomous stochastic One-Dimensional Turbulence (ODT) model, capable of simulating the full bandwidth of time and length-scales in a 1-D domain, is supplemented with large-scale 3-D information coming from a very large eddy simulation (VLES) grid. ODTLES is more expensive than any other VLES, but could be cheaper than highly resolved LES or, naturally, than Direct Numerical Simulation (DNS). Unlike Reynolds-Averaged Navier–Stokes (RANS) and VLES, ODTLES does neither need a wall model, nor a damping function. The correct near-wall behavior is naturally obtained from one SGS ODT domain that is locally wall-normal. The proposed hybrid (3-D/1-D) approach allows the resolution of all relevant scales, modeling certain aspects of 3-D turbulence on the SGS scale. Here, turbulent duct flow is considered as an example, which poses a moderate challenge for traditional LES due to emerging secondary flows that manifest themselves by corner vortices that crucially depend on the accurate capturing of small and large scale motions. Preliminary results indicate a reasonable match with DNS for mean velocity profiles, although capturing secondary flow structures remains a challenge at this stage. Further refinements of the solver and modeling approach are ongoing to improve accuracy and predictive capabilities. KW - Duct flow KW - Large Eddy Simulation (LES) KW - Multiscale modeling KW - One-Dimensional KW - Turbulence (ODT) KW - ODTLES KW - Turbulence model- KW - ing Y1 - 2025 UR - https://www.cmff.hu/papers25/CMFF25_Conference_Proceedings.pdf SN - 978-615-112-002-6 PB - Budapest University of Technology and Economics CY - Budapest ER - TY - GEN A1 - Polasanapalli, Sai Ravi Gupta A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Effects of wall slip on large-scale flow in turbulent Rayleigh–Bénard convection T2 - Proceedings of the Conference on Modelling Fluid Flow CMFF’25 N2 - The current study investigates the effects of surface boundary conditions—no-slip, free-slip, and finite-slip-on flow dynamics and heat transfer inturbulent Rayleigh–Bénard (RB) convection for different Prandtl numbers. Using a three-dimensional lattice Boltzmann method (LBM) solver in direct numerical simulation (DNS) mode, simulations are performed for three Prandtl numbers Pr = 0.786, 4.38, 10 and two Rayleigh numbers Ra = 2 ×10^6 , 10^7 . The aim is to understand how surface conditions influence flow patterns, thermal mixing, and heat transfer efficiency in a cubic cavity with heated bottom and cooled top walls. Results show that free-slip conditions significantly enhance heat transfer, yielding higher Nusselt numbers due to thinner thermal boundary layers and stronger convective currents. In contrast, finite-slip conditions produce results similar to no-slip cases, indicating minimal impact for the slip lengths considered. The results demonstrate that surface boundary conditions play a role in modulating flow dynamics and heat transfer in RB convection. KW - Lattice Boltzmann method (LBM) KW - Navier-slip KW - Prandtl number effects KW - Rayleigh–Bénard (RB) convection KW - Surface boundary conditions KW - Turbulent flows Y1 - 2025 UR - https://www.cmff.hu/papers25/CMFF25_Conference_Proceedings.pdf SN - 978-615-112-002-6 PB - Budapest University of Technology and Economics CY - Budapest ER - TY - GEN A1 - Medina Méndez, Juan Ali A1 - Klein, Marten A1 - Peeters, Jurriaan W. R. A1 - Schmidt, Heiko T1 - Evaluating turbulent channel flows with rough walls : homogeneous roughness parameterization for use in a map-based turbulence model T2 - International journal of heat and fluid flow N2 - This work is focused on modeling the effects of homogeneous roughness on low-order velocity statistics in turbulent channel flows. Hydrodynamic effects due to the roughness are characterized on the basis of volume-averaging theory (VAT) and a discrete roughness element method. This theory exploits the homogeneous character of the roughness in order to reduce the complexity of the flow to its one-dimensional statistics. The formulated VAT-based roughness forcing is best suited for drag dominated surfaces. Turbulence modeling closure is achieved with a map-based turbulence model, the One-Dimensional Turbulence (ODT) model. This avoids the prescription of laws of the wall or other ad-hoc scalings, unlike in more traditional filter-based turbulence models. The modeling framework is applied on selected Reynolds number flows for likewise selected roughness topologies. Results are compared to direct numerical simulation (DNS) data available from the literature. Among others, model results are compared with those of a previously formulated parametric forcing approach (PFA) for roughness drag which involved a costly coefficient calibration linked to the roughness topology model. In ODT, the only calibration process required is the same one involved for the turbulence model parameters, i.e., similar to the ODT model application for smooth-wall flows. Despite all of the inherently implied shortcomings of a 1-D model, some appealing properties of ODT are discussed. Notably, the model is able to predict the roughness function, as well as the wall-normal profile of the Reynolds shear stress across the entire boundary layer thickness. KW - Turbulent channel KW - Roughness KW - ODT KW - Volume-averaging Y1 - 2026 UR - https://www.sciencedirect.com/science/article/pii/S0142727X25003716#d1e18585 U6 - https://doi.org/10.1016/j.ijheatfluidflow.2025.110113 VL - 117, Part B SP - 1 EP - 21 PB - Elsevier BV CY - Amsterdam ER - TY - GEN A1 - Medina Méndez, Juan Alí A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Fractal roughness representation in a stochastic one-dimensional turbulence modeling approach T2 - Proceedings of the 13th International Symposium on Turbulence and Shear Flow Phenomena (TSFP13), Montréal, Canada, June 25-28, 2024 Y1 - 2024 UR - http://www.tsfp-conference.org/proceedings/2023/171.pdf SP - 1 EP - 6 ER - TY - GEN A1 - Klein, Marten A1 - Haque, Zubaer A1 - Schmidt, Heiko T1 - Map-based stochastic turbulence modeling for utilization in wind engineering T2 - IFAC-PapersOnLine N2 - Aeroelastic simulation tools provide means for modeling wind energy systems and their response to control actions, but these tools are notably limited by the representation of the atmospheric turbulence variability under changing conditions. The objective of this study is to assess the potential for more realistic fluctuation modeling by utilizing stochastic one-dimensional turbulence (ODT). As preliminary step towards control-oriented applications, wind speed fuctuations generated by ODT are compared to those from a state-of-the-art model, such as TurbSim. It is demonstrated that weak excursions are statistically similar, whereas ODT offers a broader variability range and enhanced turbulence intermittency features. KW - Boundary element method KW - Computer-aided engineering KW - Control applications KW - Dynamic models KW - Stochastic modeling KW - Turbulence KW - Variability Y1 - 2025 U6 - https://doi.org/10.1016/j.ifacol.2025.12.046 SN - 2405-8963 VL - 59 IS - 26 SP - 271 EP - 276 PB - Elsevier BV CY - Amsterdam ER - TY - GEN A1 - Yap, Li Toong A1 - Klein, Marten A1 - Medina Méndez, Juan A. A1 - Schmidt, Heiko T1 - Towards an improved wall function formulation for Reynolds-Averaged Navier–Stokes simulations of turbulent concentric coaxial pipe flows T2 - Proceedings in applied mathematics and mechanics : special issue: 95th Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM) N2 - Concentric coaxial (annular) pipe flow is numerically investigated using a high Reynolds number (HRN) Reynolds-Averaged Navier–Stokes (RANS) approach, given direct numerical simulation (DNS) boundary conditions. Previous work has shown that traditional wall models fail in predicting bulk quantities due to insufficient representation of the inner wall. The main objective is to assess the suitability of RANS for prediction of the flowfield if a wall function that captures the effect of the inner wall spanwise curvature at small radius ratios is provided. As a starting point, the mixing length model is used as the RANS turbulence model. The results suggest that while improved mean flow statistics can potentially be obtained, an accurate wall model representation is insufficient for capturing the mean flow in terms of the location of the velocity maximum properly. Y1 - 2025 U6 - https://doi.org/10.1002/pamm.70025 SN - 1617-7061 VL - 25 IS - 4 SP - 1 EP - 7 PB - Wiley CY - Weinheim ER - TY - GEN A1 - Tsai, Pei-Yun A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Numerical simulation of turbulent concentric annular pipe flow using one-dimensional turbulence (ODT) : part 1 : momentum transfer T2 - International journal of heat and fluid flow N2 - Turbulent concentric coaxial (annular) pipe flow is numerically investigated using a stochastic one-dimensional turbulence (ODT) model as standalone tool. The dimensionally reduced ODT domain enables fully resolved numerical simulations of the flow across the radial gap between the cylindrical inner wall and the cylindrical outer wall. The model is calibrated with available reference data at low bulk Reynolds number for a wide (radius ratio ) and a moderate () gap. Making use of the model’s predictive capabilities, radius ratio and Reynolds number effects are investigated, reaching bulk Reynolds numbers as large as . Despite the large values reached, spanwise wall-curvature effects remain sensible in the momentum boundary layer. The effects are more pronounced for larger wall curvature and to leading orders restricted to the convex cylindrical inner wall. Wall-curvature corrections to the law of the wall are obtained for both the viscous and Reynolds-stress dominated regions by fitting analytically derived expressions for the flow profile to the stochastic simulation data, demonstrating physical compatibility with Reynolds-averaged Navier–Stokes flow. Second-order and detailed fluctuation statistics demonstrate the permeating and nonlocal influence of spanwise wall curvature on the turbulent boundary layer. Surrogate model output in terms of conditional eddy event statistics reveals that the disparity between the near-inner and near-outer wall turbulence increases with Reynolds number for small radius ratios, suggesting that annular pipe flows require wall-curvature-aware wall models even at very large Reynolds numbers. KW - Concentric coaxial annulus KW - Spanwise wall curvature KW - Stochastic modeling KW - Turbulence statistics KW - Turbulent boundary layer Y1 - 2026 U6 - https://doi.org/10.1016/j.ijheatfluidflow.2026.110281 SN - 1879-2278 VL - 119 SP - 1 EP - 13 PB - Elsevier BV CY - Amsterdam ER - TY - GEN A1 - Tsai, Pei-Yun A1 - Yap, Li Toong A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Investigation of radius ratio effects on velocity statistics in annular pipe flow using one-dimensional turbulence T2 - Proceedings of the Conference on Modelling Fluid Flow CMFF’25 Y1 - 2025 UR - https://www.cmff.hu/papers25/CMFF25_Conference_Proceedings.pdf SN - 978-615-112-002-6 SP - 304 EP - 311 PB - Budapest University of Technology and Economics CY - Budapest, Hungary ER - TY - GEN A1 - Joshi, Abhishek A1 - Klein, Marten A1 - Schmidt, Heiko T1 - Non‐negligible influence of forcing mechanisms on turbulent mixing at low Reynolds numbers : a one‐dimensional turbulence study T2 - Proceedings in applied mathematics and mechanics : PAMM N2 - This study presents a numerical investigation of passive scalar mixing in homogeneous isotropic turbulence (HIT). Different volumetric forcing schemes have been used in the literature, but the side effects are rarely discussed, either because these are assumed irrelevant or because it is too costly to conduct such an analysis with a high‐fidelity model. In this study, we have used One‐Dimensional Turbulence (ODT) model to compare forcing schemes at low Reynolds numbers. Our analysis reveals critical flaws in the linear forcing model when applied to ODT. While both schemes exhibit spectral deviations from direct numerical simulation (DNS), the stochastic forcing scheme demonstrates superior dynamic fidelity, better capturing the turbulent energy cascade. In contrast, the linear forcing scheme suffers from a non‐physical energy deficit at large scales and is approximately 10 times more computationally expensive. These artefacts directly impact scalar mixing: The stochastic scheme produces classic, multi‐scale intermittency, whereas linear forcing generates extreme gradients confined only at the dissipative scales. These results demonstrate that the choice of forcing is a critical modelling decision in ODT, leading to fundamentally different model‐dependent artifacts in both turbulence dynamics and scalar mixing statistics, at least in low Reynolds number regimes. KW - Homogeneous isotropic turbulence (HIT) KW - Turbulent mixing KW - Stochastic modeling KW - One-dimensional turbulence KW - Forcing schemes Y1 - 2026 U6 - https://doi.org/https://doi.org/10.1002/pamm.70073 SN - 1617-7061 VL - 26 IS - 1 SP - 1 EP - 11 PB - Wiley CY - Weinheim ER - TY - GEN A1 - Polasanapalli, Sai Ravi Gupta A1 - Klein, Marten A1 - Schmidt, Heiko T1 - The role of slip in turbulent thermal convection Y1 - 2025 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Polasanapalli_2025_OpenLB_Poster.pdf CY - Marseille, France ER - TY - CHAP A1 - Klein, Marten A1 - Glawe, Christoph A1 - Ehlert, Mark Simon A1 - Medina Méndez, Juan Alí A1 - Schmidt, Heiko ED - Dillmann, Andreas ED - Heller, Gerd ED - Krämer, Ewald ED - Breitsamer, Christian ED - Wagner, Claus ED - Krenkel, Lars T1 - Stochastic modeling of intermittent inflow turbulence in the atmospheric boundary layer T2 - New Results in Numerical and Experimental Fluid Mechanics XV : contributions to the 24th STAB/DGLR Symposium, Regensburg, Germany, 2024 N2 - Wind turbine predesign is challenged by the representation of site-specific wind conditions. A good deal of that challenge lies in the modeling of the inflow turbulence in the atmospheric boundary layer (ABL). A stochastic one-dimensional turbulence (ODT) model is applied to an idealized neutrally stratified ABL and evolves the instantaneous velocity profile with full-scale resolution. The model is able to reproduce the law of the wall consistently after an initial calibration with the surface drag law. Investigating turbulent time series of the horizontal velocity components it is demonstrated that the model generates physically justified intermittency features with increasing turbulence intensity. KW - Atmospheric boundary layer KW - Intermittency KW - Stochastic modeling KW - Turbulent inflow Y1 - 2026 SN - 978-3-032-11115-9 U6 - https://doi.org/10.1007/978-3-032-11115-9_63 SN - 1612-2909 SP - 684 EP - 693 PB - Springer Nature Switzerland CY - Cham ER - TY - CHAP A1 - Polasanapalli, Sai Ravi Gupta A1 - Klein, Marten A1 - Schmidt, Heiko ED - Dillmann, Andreas ED - Heller, Gerd ED - Heller, Ewald ED - Breitsamer, Christian ED - Wagner, Claus ED - Krenkel, Lars T1 - Investigating slip-velocity boundary conditions in turbulent thermal convection using a lattice Boltzmann method T2 - New Results in Numerical and Experimental Fluid Mechanics XV : contributions to the 24th STAB/DGLR Symposium, Regensburg, Germany, 2024 N2 - The present study investigates the impact of various surface boundary conditions on turbulent Rayleigh–Bénard convection within a cubic cavity configuration. Simulations are conducted with a characteristic-based off-lattice Boltzmann method (LBM) solver for mildly turbulent flow of water using a direct numerical simulation (DNS) approach. The current study considers different boundary conditions such as no-slip, free-slip, and Navier-slip conditions on the walls with variations in slip length and wall-slip anisotropy. Results are evaluated through mean isotherms, streamlines, root-mean-square fluctuations, and Nusselt number. The results obtained demonstrate that the selection of wall-boundary conditions has a significant influence on the flow organization within the cavity and on the heat transfer across it. KW - Rayleigh-Bénard convection KW - Navier-slip condition KW - lattice Boltzmann method Y1 - 2026 SN - 978-3-032-11115-9 U6 - https://doi.org/10.1007/978-3-032-11115-9_9 SN - 1612-2909 SP - 90 EP - 100 PB - Springer Nature Switzerland CY - Cham ER - TY - CHAP A1 - Naik Burye, Nishidh Shailesh A1 - Medina Méndez, Juan Alí A1 - Klein, Marten A1 - Schmidt, Heiko ED - Dillmann, Andreas ED - Heller, Gerd ED - Krämer, Ewald ED - Breitsamer, Christian ED - Wagner, Claus ED - Krenkel, Lars T1 - Revisiting near-wall modeling of fully developed turbulent flow in concentric annuli T2 - New Results in Numerical and Experimental Fluid Mechanics XV : contributions to the 24th STAB/DGLR Symposium, Regensburg, Germany, 2024 N2 - We report on a systematic study for Reynolds–Averaged Navier-Stokes (RANS) modeling and simulations of turbulent annular pipe flow. Several simulations were performed using the most readily-available RANS models in the open-source library OpenFOAM. A customized 1-D RANS solver was also developed for ease of analysis. The focus of the study is on the reproduction of the mean velocity profile, its maximum, and maximum radial location, as well as modeled low-order fluctuation statistics. The flow in the annular gap is characterized by a radius ratio of 0.1, and a friction Reynolds number equal to 600 that is based on a mean friction velocity. Deviations from the mean velocity profile are observed for all RANS models investigated when compared with Direct Numerical Simulation (DNS) reference data. The representation of the near-wall outer cylinder flow is better than that of the near-wall inner cylinder flow. KW - Annular pipe flow KW - HRN and LRN wall model formulations KW - Wall function KW - Reynolds-averaged Navier-Stokes (RANS) modeling Y1 - 2026 SN - 978-3-032-11115-9 U6 - https://doi.org/10.1007/978-3-032-11115-9_68 SN - 1612-2909 SP - 737 EP - 747 PB - Springer Nature Switzerland CY - Cham ER -