@misc{Klein, author = {Klein, Marten}, title = {Map-based stochastic simulation data of a transient Ekman boundary layer}, abstract = {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.}, language = {en} } @misc{PolasanapalliKleinSchmidt, author = {Polasanapalli, Sai Ravi Gupta and Klein, Marten and Schmidt, Heiko}, title = {Towards stochastic subgrid-scale modeling of turbulent thermal convection in an under-resolved off-lattice Boltzmann method}, series = {Proceedings in applied mathematics and mechanics : PAMM}, journal = {Proceedings in applied mathematics and mechanics : PAMM}, issn = {1617-7061}, doi = {10.1002/pamm.202300223}, pages = {1 -- 9}, abstract = {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.}, language = {en} } @misc{KleinZenkerStaricketal., author = {Klein, Marten and Zenker, Christian and Starick, Tommy and Schmidt, Heiko}, title = {Stochastic modeling of multiple scalar mixing in a three-stream concentric coaxial jet based on one-dimensional turbulence}, series = {International Journal of Heat and Fluid Flow}, volume = {104}, journal = {International Journal of Heat and Fluid Flow}, issn = {0142-727X}, doi = {10.1016/j.ijheatfluidflow.2023.109235}, pages = {1 -- 17}, abstract = {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.}, language = {en} } @misc{TsaiSchmidtKlein, author = {Tsai, Pei-Yun and Schmidt, Heiko and Klein, Marten}, title = {Investigating Reynolds number effects in turbulent concentric coaxial pipe flow using stochastic one-dimensional turbulence modeling}, series = {Proceedings in Applied Mathematics and Mechanics}, volume = {23}, journal = {Proceedings in Applied Mathematics and Mechanics}, number = {4}, issn = {1617-7061}, doi = {10.1002/pamm.202300167}, pages = {1 -- 8}, abstract = {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.}, language = {en} } @misc{KleinStarickZenkeretal., author = {Klein, Marten and Starick, Tommy and Zenker, Christian and Medina M{\´e}ndez, Juan Al{\´i} and Schmidt, Heiko}, title = {Reduced order stochastic modeling of turbulent mixing based on conservative baker's maps}, series = {Proceedings of the 14th International ERCOFTAC Symposium on Engineering Turbulence Modelling and Measurements (ETMM-14)}, journal = {Proceedings of the 14th International ERCOFTAC Symposium on Engineering Turbulence Modelling and Measurements (ETMM-14)}, publisher = {ERCOFTAC}, address = {Barcelona, Spain}, pages = {613 -- 618}, abstract = {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.}, language = {en} } @misc{VallemKleinSchmidt, author = {Vallem, Rishindra and Klein, Marten and Schmidt, Heiko}, title = {Numerical modeling and simulation of two-phase internal flow instabilities using Smoothed Particle Hydrodynamics (SPH)}, series = {STAB Jahresbericht 2023}, volume = {21/2023}, journal = {STAB Jahresbericht 2023}, publisher = {Deutsche Str{\"o}mungsmechanische Arbeitsgemeinschaft (STAB)}, address = {G{\"o}ttingen, Germany}, pages = {158 -- 159}, language = {en} } @misc{TsaiSchmidtKlein, author = {Tsai, Pei-Yun and Schmidt, Heiko and Klein, Marten}, title = {Stochastic modeling of asymmetric turbulent boundary layers in annular pipe flow}, doi = {10.13140/RG.2.2.18789.78567}, pages = {1}, language = {en} } @misc{KleinMedinaMendezSchmidt, author = {Klein, Marten and Medina M{\´e}ndez, Juan Al{\´i} and Schmidt, Heiko}, title = {Stochastic modeling of electrohydrodynamically enhanced drag in one-way and fully coupled turbulent Poiseuille and Couette flow}, series = {Technische Mechanik}, volume = {43}, journal = {Technische Mechanik}, number = {1}, issn = {0232-3869}, doi = {10.24352/UB.OVGU-2023-049}, pages = {111 -- 127}, abstract = {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.}, language = {en} } @misc{KleinSchmidt, author = {Klein, Marten and Schmidt, Heiko}, title = {Capturing features of turbulent Ekman-Stokes boundary layers with a stochastic modeling approach}, series = {Advances in Science and Research}, volume = {20}, journal = {Advances in Science and Research}, issn = {1992-0636}, doi = {10.5194/asr-20-55-2023}, pages = {55 -- 64}, abstract = {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.}, language = {en} } @misc{MedinaMendezKleinSchoepsetal., author = {Medina M{\´e}ndez, Juan Ali and Klein, Marten and Sch{\"o}ps, Mark Simon and Schmidt, Heiko}, title = {Predicting volatile wind energy: Stochastic forward modeling and machine learning}, series = {86. Jahrestagung der DPG (86th Annual Conference of the DPG), DPG-Fr{\"u}hjahrstagung 2023, (DPG Spring Meeting 2023 of the Matter and Cosmos Section (SMuK), 20-24 March 2023, Technische Universit{\"a}t Dresden}, journal = {86. Jahrestagung der DPG (86th Annual Conference of the DPG), DPG-Fr{\"u}hjahrstagung 2023, (DPG Spring Meeting 2023 of the Matter and Cosmos Section (SMuK), 20-24 March 2023, Technische Universit{\"a}t Dresden}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {2751-0522}, pages = {S. 343}, language = {en} } @misc{TsaiSchmidtKlein, author = {Tsai, Pei-Yun and Schmidt, Heiko and Klein, Marten}, title = {Stochastic modeling and theoretical analysis of weakly heated concentric coaxial pipe flows at low prandtl number}, series = {Proceedings in Applied Mathematics and Mechanics}, volume = {25}, journal = {Proceedings in Applied Mathematics and Mechanics}, number = {1}, publisher = {Wiley}, address = {Weinheim}, issn = {1617-7061}, doi = {10.1002/pamm.70006}, pages = {1 -- 7}, abstract = {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.}, language = {en} } @misc{MarinkovićMedinaSchoepsetal., author = {Marinković, Pavle and Medina, Juan A. and Sch{\"o}ps, Mark Simon and Klein, Marten and Schmidt, Heiko}, title = {Experiences from the bottom-up development of an object-oriented CFD solver with prospective hybrid turbulence model applications}, series = {Proceedings in Applied Mathematics and Mechanics}, volume = {25}, journal = {Proceedings in Applied Mathematics and Mechanics}, number = {1}, publisher = {Wiley}, issn = {1617-7061}, doi = {10.1002/pamm.202400190}, abstract = {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.}, language = {en} } @misc{KleinMedinaMendezSchmidt, author = {Klein, Marten and Medina M{\´e}ndez, Juan Al{\´i} and Schmidt, Heiko}, title = {Simulating Volatile Wind Energy: Stochastic Forward Modeling and Machine Learning}, publisher = {Innovation Hub 13, TH Wildau}, address = {Wildau}, pages = {1}, abstract = {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}, language = {en} } @misc{LiKleinSchmidt, author = {Li, Hanchen and Klein, Marten and Schmidt, Heiko}, title = {Simulation of radiatively driven mixing in a smoke cloud using "one-dimensional turbulence"}, doi = {10.5194/egusphere-egu25-9491}, pages = {1}, abstract = {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).}, language = {en} } @misc{KleinSchmidt, author = {Klein, Marten and Schmidt, Heiko}, title = {Investigating cutoff scales in turbulent Ekman flow with a map-based stochastic modeling approach}, publisher = {Copernicus GmbH}, address = {G{\"o}ttingen}, doi = {10.5194/egusphere-egu25-13495}, pages = {1}, abstract = {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.}, language = {en} } @misc{MarinkovicMedinaKleinetal., author = {Marinkovic, Pavle and Medina, Juan and Klein, Marten and Schmidt, Heiko}, title = {Application of extended large-eddy simualtion (XLES) to turbulent channel flow}, series = {Proceedings in applied mathematics and mechanics : PAMM}, volume = {25 : special issue : 95th Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM)}, journal = {Proceedings in applied mathematics and mechanics : PAMM}, number = {2}, publisher = {Wiley}, address = {Weinheim}, issn = {1617-7061}, doi = {10.1002/pamm.70010}, pages = {1 -- 7}, abstract = {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.}, language = {en} } @misc{MarinkovicMedinaMendezKleinetal., author = {Marinkovic, Pavle and Medina M{\´e}ndez, Juan A. and Klein, Marten and Schmidt, Heiko}, title = {ODTLES : large-eddy simulation with autonomous stochastic subgrid-scale modeling applied to turbulent duct flow}, series = {Proceedings of the Conference on Modelling Fluid Flow CMFF'25}, journal = {Proceedings of the Conference on Modelling Fluid Flow CMFF'25}, publisher = {Budapest University of Technology and Economics}, address = {Budapest}, isbn = {978-615-112-002-6}, pages = {8}, abstract = {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.}, language = {en} } @misc{PolasanapalliKleinSchmidt, author = {Polasanapalli, Sai Ravi Gupta and Klein, Marten and Schmidt, Heiko}, title = {Effects of wall slip on large-scale flow in turbulent Rayleigh-B{\´e}nard convection}, series = {Proceedings of the Conference on Modelling Fluid Flow CMFF'25}, journal = {Proceedings of the Conference on Modelling Fluid Flow CMFF'25}, publisher = {Budapest University of Technology and Economics}, address = {Budapest}, isbn = {978-615-112-002-6}, pages = {8}, abstract = {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-B{\´e}nard (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.}, language = {en} } @misc{MedinaMendezKleinPeetersetal., author = {Medina M{\´e}ndez, Juan Ali and Klein, Marten and Peeters, Jurriaan W. R. and Schmidt, Heiko}, title = {Evaluating turbulent channel flows with rough walls : homogeneous roughness parameterization for use in a map-based turbulence model}, series = {International journal of heat and fluid flow}, volume = {117, Part B}, journal = {International journal of heat and fluid flow}, publisher = {Elsevier BV}, address = {Amsterdam}, doi = {10.1016/j.ijheatfluidflow.2025.110113}, pages = {1 -- 21}, abstract = {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.}, language = {en} } @misc{MedinaMendezKleinSchmidt, author = {Medina M{\´e}ndez, Juan Al{\´i} and Klein, Marten and Schmidt, Heiko}, title = {Fractal roughness representation in a stochastic one-dimensional turbulence modeling approach}, series = {Proceedings of the 13th International Symposium on Turbulence and Shear Flow Phenomena (TSFP13), Montr{\´e}al, Canada, June 25-28, 2024}, journal = {Proceedings of the 13th International Symposium on Turbulence and Shear Flow Phenomena (TSFP13), Montr{\´e}al, Canada, June 25-28, 2024}, pages = {1 -- 6}, language = {en} } @misc{KleinHaqueSchmidt, author = {Klein, Marten and Haque, Zubaer and Schmidt, Heiko}, title = {Map-based stochastic turbulence modeling for utilization in wind engineering}, series = {IFAC-PapersOnLine}, volume = {59}, journal = {IFAC-PapersOnLine}, number = {26}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {2405-8963}, doi = {10.1016/j.ifacol.2025.12.046}, pages = {271 -- 276}, abstract = {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.}, language = {en} } @misc{YapKleinMedinaMendezetal., author = {Yap, Li Toong and Klein, Marten and Medina M{\´e}ndez, Juan A. and Schmidt, Heiko}, title = {Towards an improved wall function formulation for Reynolds-Averaged Navier-Stokes simulations of turbulent concentric coaxial pipe flows}, series = {Proceedings in applied mathematics and mechanics : special issue: 95th Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM)}, volume = {25}, journal = {Proceedings in applied mathematics and mechanics : special issue: 95th Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM)}, number = {4}, publisher = {Wiley}, address = {Weinheim}, issn = {1617-7061}, doi = {10.1002/pamm.70025}, pages = {1 -- 7}, abstract = {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.}, language = {en} } @misc{TsaiKleinSchmidt, author = {Tsai, Pei-Yun and Klein, Marten and Schmidt, Heiko}, title = {Numerical simulation of turbulent concentric annular pipe flow using one-dimensional turbulence (ODT) : part 1 : momentum transfer}, series = {International journal of heat and fluid flow}, volume = {119}, journal = {International journal of heat and fluid flow}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {1879-2278}, doi = {10.1016/j.ijheatfluidflow.2026.110281}, pages = {1 -- 13}, abstract = {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.}, language = {en} } @misc{TsaiYapKleinetal., author = {Tsai, Pei-Yun and Yap, Li Toong and Klein, Marten and Schmidt, Heiko}, title = {Investigation of radius ratio effects on velocity statistics in annular pipe flow using one-dimensional turbulence}, series = {Proceedings of the Conference on Modelling Fluid Flow CMFF'25}, journal = {Proceedings of the Conference on Modelling Fluid Flow CMFF'25}, publisher = {Budapest University of Technology and Economics}, address = {Budapest, Hungary}, isbn = {978-615-112-002-6}, pages = {304 -- 311}, language = {en} } @misc{JoshiKleinSchmidt, author = {Joshi, Abhishek and Klein, Marten and Schmidt, Heiko}, title = {Non-negligible influence of forcing mechanisms on turbulent mixing at low Reynolds numbers : a one-dimensional turbulence study}, series = {Proceedings in applied mathematics and mechanics : PAMM}, volume = {26}, journal = {Proceedings in applied mathematics and mechanics : PAMM}, number = {1}, publisher = {Wiley}, address = {Weinheim}, issn = {1617-7061}, doi = {https://doi.org/10.1002/pamm.70073}, pages = {1 -- 11}, abstract = {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.}, language = {en} } @misc{PolasanapalliKleinSchmidt, author = {Polasanapalli, Sai Ravi Gupta and Klein, Marten and Schmidt, Heiko}, title = {The role of slip in turbulent thermal convection}, address = {Marseille, France}, language = {en} } @incollection{KleinGlaweEhlertetal., author = {Klein, Marten and Glawe, Christoph and Ehlert, Mark Simon and Medina M{\´e}ndez, Juan Al{\´i} and Schmidt, Heiko}, title = {Stochastic modeling of intermittent inflow turbulence in the atmospheric boundary layer}, series = {New Results in Numerical and Experimental Fluid Mechanics XV : contributions to the 24th STAB/DGLR Symposium, Regensburg, Germany, 2024}, booktitle = {New Results in Numerical and Experimental Fluid Mechanics XV : contributions to the 24th STAB/DGLR Symposium, Regensburg, Germany, 2024}, editor = {Dillmann, Andreas and Heller, Gerd and Kr{\"a}mer, Ewald and Breitsamer, Christian and Wagner, Claus and Krenkel, Lars}, publisher = {Springer Nature Switzerland}, address = {Cham}, isbn = {978-3-032-11115-9}, issn = {1612-2909}, doi = {10.1007/978-3-032-11115-9_63}, pages = {684 -- 693}, abstract = {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.}, language = {en} } @incollection{PolasanapalliKleinSchmidt, author = {Polasanapalli, Sai Ravi Gupta and Klein, Marten and Schmidt, Heiko}, title = {Investigating slip-velocity boundary conditions in turbulent thermal convection using a lattice Boltzmann method}, series = {New Results in Numerical and Experimental Fluid Mechanics XV : contributions to the 24th STAB/DGLR Symposium, Regensburg, Germany, 2024}, booktitle = {New Results in Numerical and Experimental Fluid Mechanics XV : contributions to the 24th STAB/DGLR Symposium, Regensburg, Germany, 2024}, editor = {Dillmann, Andreas and Heller, Gerd and Heller, Ewald and Breitsamer, Christian and Wagner, Claus and Krenkel, Lars}, publisher = {Springer Nature Switzerland}, address = {Cham}, isbn = {978-3-032-11115-9}, issn = {1612-2909}, doi = {10.1007/978-3-032-11115-9_9}, pages = {90 -- 100}, abstract = {The present study investigates the impact of various surface boundary conditions on turbulent Rayleigh-B{\´e}nard 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.}, language = {en} } @incollection{NaikBuryeMedinaMendezKleinetal., author = {Naik Burye, Nishidh Shailesh and Medina M{\´e}ndez, Juan Al{\´i} and Klein, Marten and Schmidt, Heiko}, title = {Revisiting near-wall modeling of fully developed turbulent flow in concentric annuli}, series = {New Results in Numerical and Experimental Fluid Mechanics XV : contributions to the 24th STAB/DGLR Symposium, Regensburg, Germany, 2024}, booktitle = {New Results in Numerical and Experimental Fluid Mechanics XV : contributions to the 24th STAB/DGLR Symposium, Regensburg, Germany, 2024}, editor = {Dillmann, Andreas and Heller, Gerd and Kr{\"a}mer, Ewald and Breitsamer, Christian and Wagner, Claus and Krenkel, Lars}, publisher = {Springer Nature Switzerland}, address = {Cham}, isbn = {978-3-032-11115-9}, issn = {1612-2909}, doi = {10.1007/978-3-032-11115-9_68}, pages = {737 -- 747}, abstract = {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.}, language = {en} }