@misc{ReibleHartmannDelleSite, author = {Reible, Benedikt and Hartmann, Carsten and Delle Site, Luigi}, title = {Two-sided Bogoliubov inequality to estimate finite-size effects in quantum molecular simulations}, series = {Letters in Mathematical Physics}, volume = {112}, journal = {Letters in Mathematical Physics}, number = {5}, issn = {1573-0530}, doi = {10.1007/s11005-022-01586-3}, pages = {1 -- 17}, language = {en} } @misc{SchefflerStrehlerVargasKoch, author = {Scheffler, Robert and Strehler, Martin and Vargas Koch, Laura}, title = {Routing Games with Edge Priorities}, series = {ACM Transactions on Economics and Computation}, volume = {10}, journal = {ACM Transactions on Economics and Computation}, number = {1}, issn = {2167-8375}, doi = {10.1145/3488268}, pages = {1:1 -- 1:27}, 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{BehrangStarickWheeleretal., author = {Behrang, Masoomeh and Starick, Tommy and Wheeler, Isaac and Schmidt, Heiko and Kerstein, Alan and Lignell, David}, title = {Hierarchical parcel-swapping representation of turbulent mixing : part 4 : extension to the viscous range and to mixing of scalars with non-unity Schmidt numbers}, series = {Journal of fluid mechanics}, volume = {1020}, journal = {Journal of fluid mechanics}, publisher = {Cambridge University Press}, address = {Cambridge}, issn = {0022-1120}, doi = {doi:10.1017/jfm.2025.10512}, pages = {1 -- 39}, abstract = {Hierarchical parcel swapping (HiPS) is a multiscale stochastic model of turbulent mixing based on a binary tree. Length scales decrease geometrically with increasing tree level, and corresponding time scales follow inertial range scaling. Turbulent eddies are represented by swapping subtrees. Lowest-level swaps change fluid parcel pairings, with new pairings instantly mixed. This formulation suitable for unity Schmidt number Sc is extended to non-unity Sc. For high Sc, the tree is extended to the Batchelor level, assigning the same time scale (governing the rate of swap occurrences) to the added levels as the time scale at the base of the Sc=3 tree. For low Sc, a swap at the Obukhov-Corrsin level mixes all parcels within corresponding subtrees. Well-defined model analogues of turbulent diffusivity, and mean scalar-variance production and dissipation rates are identified. Simulations idealising stationary homogeneous turbulence with an imposed scalar gradient reproduce various statistical properties of viscous-range and inertial-range pair dispersion, and of the scalar power spectrum in the inertial-advective, inertial-diffusive and viscous-advective regimes. The viscous-range probability density functions of pair separation and scalar dissipation agree with applicable theory, including the stretched-exponential tail shape associated with viscous-range scalar intermittency. Previous observation of that tail shape for Sc=1, heretofore not modelled or explained, is reproduced. Comparisons to direct numerical simulation allow evaluation of empirical coefficients, facilitating quantitative applications. Parcel-pair mixing is a common mixing treatment, e.g. in subgrid closures for coarse-grained flow simulation, so HiPS can improve model physics simply by smarter (yet nearly cost-free) selection of pairs to be mixed.}, language = {en} } @misc{StarickSchmidt, author = {Starick, Tommy and Schmidt, Heiko}, title = {Numerical investigation of a lifted methane/air jet flame using stochastic map-based turbulence modeling}, series = {Proceedings of the Conference on Modelling Fluid Flow CMFF'25}, journal = {Proceedings of the Conference on Modelling Fluid Flow CMFF'25}, publisher = {Department of Fluid Mechanics, Faculty of Mechanical Engineering, Budapest University of Technology and Economics}, address = {Budapest}, isbn = {978-615-112-002-6}, pages = {1 -- 8}, abstract = {This numerical study investigates a lifted methane/air jet flame in a vitiated coflow by means of the map-based, stochastic one-dimensional turbulence (ODT) model. The dimensional reduction of ODT allows for simulations with affordable computational costs and provides nonetheless full-scale resolution along a notional line of sight crossing the turbulent flow field. The considered Cabra burner configuration consists of a jet flame issuing from a central nozzle into a vitiated coflow of hot combustion products. Radial and centerline profiles for mixture fraction, temperature and selected species mass fractions obtained from ODT using a reduced and detailed reaction mechanism are in appropriate agreement with the existing experimental measurements. A two-dimensional illustration of the autoignition index is given, which enables the distinction between autoignition and propagation driven reaction zones. Additionally, the sensitivity of the jet combustion to velocity and temperature variations is investigated. Considering the reduced order of ODT and the sensitivity of the subtle interactions of the hot coflow with the cold jet on the entire reaction process, ODT is able to predict the flow characteristics and reasonably matches the experimental data. As a consequence, ODT is an efficient and alternative model for turbulent reactive flow simulations.}, language = {en} } @misc{BehrangStarickSchmidtetal., author = {Behrang, Masoomeh and Starick, Tommy and Schmidt, Heiko and Lignell, David O.}, title = {A C++ library for turbulent mixing simulation using Hierarchical Parcel Swapping (HiPS)}, series = {SoftwareX}, volume = {31}, journal = {SoftwareX}, publisher = {Elsevier BV}, address = {Amsterdam}, issn = {2352-7110}, doi = {10.1016/j.softx.2025.102331}, pages = {1 -- 7}, abstract = {Turbulence models are crucial for simulating flows at all scales, capturing both large-scale structures and small-scale mixing. Software libraries that implement such models should support modular integration, customization, and scalability across different simulation frameworks. This paper presents Hierarchical Parcel Swapping (HiPS), a C++ library documented with Doxygen and available on GitHub. HiPS supports both mixing and reactions and can be used as a standalone model or as a subgrid model in CFD simulations. The code includes examples for users to run it as a standalone model. Additionally, considerations for using it as a subgrid model are provided.}, 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{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} }