TY - GEN A1 - Schmidt, Heiko A1 - Kerstein, Alan R. A1 - Nédélec, Renaud A1 - Wunsch, Scott A1 - Sayler, Ben J. T1 - Numerical study of radiatively induced entrainment T2 - Journal of Physics: Conference Series Y1 - 2011 U6 - https://doi.org/10.1088/1742-6596/318/7/072017 SN - 1742-6588 VL - 318 SP - 072017 ER - TY - GEN A1 - Schmidt, Heiko A1 - Kerstein, Alan R. A1 - Nédélec, Renaud A1 - Wunsch, Scott A1 - Sayler, Ben J. T1 - Analysis and numerical simulation of a laboratory analog of radiatively induced cloud-top entrainment T2 - Theoretical Computational Fluid Dynamics Y1 - 2012 U6 - https://doi.org/10.1007/s00162-012-0288-4 SN - 1432-2250 ER - TY - GEN A1 - Oevermann, Michael A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - HCCI combustion modeling using detailed chemistry coupled to LEM-based advection T2 - Combustion and Flame Y1 - 2008 SN - 1556-2921 VL - 155 IS - 3 SP - 370 EP - 379 ER - TY - GEN A1 - Schulz, Falko T. A1 - Glawe, Christoph A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Toward modeling of CO2 multi-phase flow patterns using a stochastic multi-scale approach T2 - Environmental Earth Sciences Y1 - 2013 U6 - https://doi.org/10.1007/s12665-013-2461-5 SN - 1866-6299 VL - 70 IS - 8 SP - 3739 EP - 3748 ER - TY - CHAP A1 - Schulz, Falko T. A1 - Glawe, Christoph A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Liquid jet simulation using one-dimensional turbulence T2 - 14th European Turbulence Conference, Lyon, France, September 1-4, 2013 Y1 - 2013 UR - http://etc14.ens-lyon.fr/etc-14-proceedings/accepted-talks/ ER - TY - CHAP A1 - Schulz, Falko T. A1 - Glawe, Christoph A1 - Kerstein, Alan R. A1 - Schmidt, Heiko T1 - Toward modeling of supercritical CO2 flow using map-based advection T2 - EGU General Assembly 2012, held 22-27 April, 2012 in Vienna Y1 - 2012 UR - http://meetingorganizer.copernicus.org/EGU2012/EGU2012-8816-1.pdf N1 - EGU2012-8816-1 ER - TY - CHAP A1 - Kerstein, Alan R. A1 - Glawe, Christoph A1 - Schmidt, Heiko A1 - Klein, Rupert A1 - Gonzalez-Juez, Esteban D. A1 - Schmidt, Rodney T1 - Computational modeling of scalar transport and buoyancy effects in turbulent flows using ODTLES T2 - Bulletin of the American Physical Society Y1 - 2012 UR - http://meeting.aps.org/Meeting/DFD12/Event/176984 N1 - 65th Annual Meeting of the APS Division of Fluid Dynamics, Sunday–Tuesday, November 18–20, 2012 San Diego, California VL - 57 IS - 17 ER - TY - CHAP A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Modeling of wind-field fluctuations using the one-dimensional-turbulence model T2 - The Science of Making Torque from Wind, Oldenburg, Germany, October 9-11, 2012 Oldenburg Germany Y1 - 2012 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/2012_Forwind_Oldenburg.pdf ER - TY - CHAP A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Towards a multiscale strategy for modeling high-pressure flow of carbon dioxide for sequestration T2 - Geoenergy 2010, Potsdam, Germany Y1 - 2010 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/2010_GeoEn_Potsdam.pdf ER - TY - CHAP A1 - Nédélec, Renaud A1 - Schmidt, Heiko A1 - Wunsch, Scott A1 - Sayler, Ben J. A1 - Kerstein, Alan R. T1 - Comparison of Entrainment Rates from a Tank Experiment with Results Us- ing the One-Dimensional-Turbulence Model T2 - EGU General Assembly 2010, held in Vienna, Austria, 02 – 07 May 2010 Y1 - 2010 UR - http://meetingorganizer.copernicus.org/EGU2010/EGU2010-378-1.pdf N1 - EGU2010-378-1 ER - TY - CHAP A1 - Oevermann, Michael A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Linear eddy modeling of n-heptane combustion in HCCI engines T2 - 12th SIAM International Conference on Numerical Combustion Y1 - 2008 UR - http://www.siam.org/meetings/nc08/prgNC08.pdf ER - TY - GEN A1 - Schmidt, Heiko A1 - Kerstein, Alan R. A1 - Nédélec, Renaud A1 - Wunsch, Scott A1 - Sayler, Ben J. T1 - One-dimensional turbulence simulation of a laboratory analog of radiatively induced cloud-top entrainment Y1 - 2011 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/2011_Metstroem_Berlin.pdf N1 - MetStröm Conference 2011 on Multiple Scales in Fluid Dynamics and Meteorology ER - TY - CHAP A1 - Schmidt, Heiko A1 - Schulz, Falko T. A1 - Kerstein, Alan R. T1 - Toward modeling of multi- phase flow patterns using a combination of level sets and one-dimensional turbulence T2 - EGU General Assembly 2011, Vienna, Austria, 03 – 08 April 2011 Y1 - 2011 UR - http://meetingorganizer.copernicus.org/EGU2011/EGU2011-10258.pdf N1 - EGU2011-10258 ER - TY - GEN A1 - Kerstein, Alan R. A1 - Schmidt, Heiko A1 - Nédélec, Renaud A1 - Wunsch, Scott A1 - Sayler, Ben J. T1 - Analysis and numerical simulation of a laboratory analog of radiatively induced cloud-top entrainment T2 - Bulletin of the American Physical Society Dynamics Y1 - 2010 UR - http://meetings.aps.org/Meeting/DFD10/Event/133814 N1 - 63rd Annual Meeting of the APS Division of Fluid Dynamics, November 21–23, 2010, Long Beach, California VL - 55 IS - 16 ER - TY - CHAP A1 - Glawe, Christoph A1 - Klein, Rupert A1 - Kerstein, Alan R. A1 - Schmidt, Heiko T1 - Towards the simulation of gravity waves using the One-Dimensional Turbulence model T2 - EGU General Assembly 2012, held 22-27 April, 2012 in Vienna Y1 - 2012 UR - http://meetingorganizer.copernicus.org/EGU2012/EGU2012-4821.pdf N1 - EGU2012-4821 ER - TY - CHAP A1 - Movaghar, Amirreza A1 - Linne, Mark A1 - Oevermann, Michael A1 - Meiselbach, Falko T. A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Numerical study of liquid breakup at the surface of turbulent liquid jets using One-Dimensional Turbulence T2 - 26th Annual Conference on Liquid Atomization and Spray Systems, ILASS, proceedings of the Conference, Bremen, Germany, 08.09.2014 - 10.09.2014 N2 - This paper presents an investigation of primary breakup of planar turbulent liquid jets and breakup properties at the surface of turbulent jets in still air at standard conditions. Numerical simulations are carried out for jet exit Reynolds number 23000 and Weber numbers in the range [102–107]. Due to the limitation of direct numerical simulation (DNS) to moderate Reynolds numbers, a stochastic 1D ansatz based on the one-dimensional turbulence (ODT) model is used to simulate a planar liquid jet with a high lateral resolution. ODT permits an affordable high resolution of interface and single-phase property gradients which are key for understanding the local behavior. ODT is a stochastic model simulating turbulent flow evolution along a notional 1D line of sight by applying instantaneous maps to represent the effect of individual turbulent eddies on property profiles. The most relevant mechanisms that influence the primary breakup of liquid jets are found to be represented accurately based on comparisons to experiments and correlations reported in the literature. Building on this finding, future work will focus on the statistics of droplets generated by primary breakup, both to investigate their relationship to breakup mechanisms and to provide input to models of secondary breakup and subsequent spray evolution. Y1 - 2014 SN - 978-3-00-047070-7 CY - Bremen ER - TY - CHAP A1 - Glawe, Christoph A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - ODTLES: Mulitscale turbulence modeling and buoyant application T2 - Book of abstracts, 7th European Postgraduate Fluid Dynamics Conference, Ilmenau, Germany, 14th - 17th, July 2014 Y1 - 2014 CY - Ilmenau ER - TY - GEN A1 - Jozefik, Zoltan A1 - Kerstein, Alan R. A1 - Schmidt, Heiko A1 - Lyra, Sgouria A1 - Kolla, Hemanth A1 - Chen, Jackie H. T1 - One-dimensional turbulence modeling of a turbulent counterflow flame with comparison to DNS T2 - Combustion and Flame Y1 - 2014 SN - 1556-2921 VL - 162 IS - 8 SP - 2999 EP - 3015 ER - TY - GEN A1 - Schmidt, Heiko A1 - Glawe, Christoph A1 - Jozefik, Zoltan A1 - Meiselbach, Falko T. A1 - Kerstein, Alan R. T1 - On the benefits of ODT-based stochastic turbulence modeling T2 - Proceedings in applied mathematics and mechanics : PAMM N2 - We summarize the group’s progress in applying, analyzing, and improving ODT and ODT-based stochastic turbulence models like ODTLES. Compared to DNS these models span a wider range of scales while compared to RANS/LES (i) the molecular effects are retained and (ii) no assumption of scale separation is made. In this regard ODTLES has more properties of DNS than of standard LES. Y1 - 2014 SN - 1617-7061 VL - 14 IS - 1 SP - 655 EP - 656 ER - TY - CHAP A1 - Jozefik, Zoltan A1 - Kerstein, Alan R. A1 - Schmidt, Heiko ED - King, Rudibert T1 - Towards a compressible reactive multiscale approach based on One-Dimensional Turbulence T2 - Active Flow and Combustion Control 2014 N2 - Due to its huge complexity, progress in understanding and prediction of turbulent combustion is extremely challenging. In principle, progress is possible without improved understanding through direct numerical solution (DNS) of the exact governing equations, but the wide range of spatial and temporal scales often renders it unaffordable, so coarse-grained 3D numerical simulations with subgrid parameterization of the unresolved scales are often used. This is especially problematic for multi-physics regimes such as reacting flows because much of the complexity is thus relegated to the unresolved small scales. One-Dimensional Turbulence (ODT) is an alternative stochastic model for turbulent flow simulation. It operates on a 1D spatial domain via time advancing individual flow realizations rather than ensemble-averaged quantities. The lack of spatial and temporal filtering on this 1D domain enables a physically sound multiscale treatment which is especially useful for combustion applications where, e.g., sharp interfaces or small chemical time scales have to be resolved. Lignell et al. recently introduced an efficient ODT implementation using an adaptive mesh. As all existing ODT versions it operates in the incompressible regime and thus cannot handle compressibility effects and their interactions with turbulence and chemistry which complicate the physical picture even further. In this paper we make a first step toward an extension of the ODT methodology towards an efficient compressible implementation. The necessary algorithmic changes are highlighted and preliminary results for a standard non-reactive shock tube problem as well as for a turbulent reactive case illustrate the potential of the extended approach. Y1 - 2014 SN - 978-3-319-11967-0 SN - 978-3-319-11966-3 SP - 197 EP - 211 PB - Springer CY - Switzerland ER - TY - CHAP A1 - Glawe, Christoph A1 - Schulz, Falko T. A1 - Gonzalez-Juez, Esteban D. A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - ODTLES Simulations of Turbulent Flows through Heated Channels and Ducts T2 - 8th International Symposium on turbulence and shear flow phenomena (TSFP8), 28–30 August 2013, Poitiers, France, vol. 2 N2 - A widely occurring problem in fluid dynamics either in engineering or e.g. hydrology is the turbulent transport through channels and ducts. ODTLES, a stochastic based multi-scale and multi-dimensional model, is a promising tool to describe these flows even including scalar proper- ties like temperature. We are quantifying the ability of ODTLES to describe the heated channel flow with respect to the Prandtl number and the flow through squared ducts with respect to the Reynolds number. Y1 - 2013 UR - http://www.tsfp-conference.org/proceedings/2013/v2/htc.pdf SP - 1 EP - 6 ER - TY - GEN A1 - Jozefik, Zoltan A1 - Kerstein, Alan R. A1 - Schmidt, Heiko A1 - Lyra, Sgouria A1 - Kolla, Hemanth A1 - Chen, Jackie H. T1 - One-dimensional turbulence modeling of a turbulent counterflow flame with comparison to DNS T2 - Combustion and Flame N2 - The one-dimensional turbulence (ODT) model is applied to a reactant-to-product counterflow configuration and results are compared with DNS data. The model employed herein solves conservation equations for momentum, energy, and species on a one dimensional (1D) domain corresponding to the line spanning the domain between nozzle orifice centers. The effects of turbulent mixing are modeled via a stochastic process, while the Kolmogorov and reactive length and time scales are explicitly resolved and a detailed chemical kinetic mechanism is used. Comparisons between model and DNS results for spatial mean and root-mean-square (RMS) velocity, temperature, and major and minor species profiles are shown. The ODT approach shows qualitatively and quantitatively reasonable agreement with the DNS data. Scatter plots and statistics conditioned on temperature are also compared for heat release rate and all species. ODT is able to capture the range of results depicted by DNS. However, conditional statistics show signs of underignition. Y1 - 2015 U6 - https://doi.org/10.1016/j.combustflame.2015.05.010 SN - 0010-2180 VL - 162 IS - 8 SP - 2999 EP - 3015 ER - TY - GEN A1 - Jozefik, Zoltan A1 - Kerstein, Alan R. A1 - Schmidt, Heiko T1 - Simulation of shock–turbulence interaction in non-reactive flow and in turbulent deflagration and detonation regimes using one-dimensional turbulence T2 - Combustion and Flame N2 - The one-dimensional turbulence (ODT) methodology is extended to include an efficient compressible implementation and a model for capturing shock-induced turbulence is presented. Lignell et al. recently introduced a Lagrangian ODT implementation using an adaptive mesh. As the code operates in the incompressible regime (apart from constant-pressure dilatation) it cannot handle compressibility effects and their interactions with turbulence and chemistry. The necessary algorithmic changes to include compressibility effects are highlighted and our model for capturing shock- turbulence interaction is presented. To validate our compressible solver, we compare results for the Sod shock tube problem against a finite volume Riemannsolver. To validate our model for shock–turbulence interaction, we present comparisons for a non-reactive and a reactive case. First, results of a shock traveling from light (air) to heavy (SF6) with recheck have been simulated to match mixing width growth data of experiments and turbulent kinetic energy results from LES.Then, for one-step chemistry calibrated to represent an acetylene/airmixture we simulate the interaction of a shock wave with an expanding flame front, and compare results with 2D simulation (2D-sim) data for flame brush formation and ensuing deflagration-to-detonation transitions (DDT). Results for the Sod shock tube comparison show that the shock speed and profile are captured accurately. Results for the non-reactive shock–recheck problem show that interface growth at all simulated Mach numbers is captured accurately and that the turbulent kinetic energy agrees in order of magnitude with LES data. The reactive shock tube results show that the flame brush thickness compares well to 2D-sim data and that the approximate location and timing of the DDT can be captured. The known sensitivity of DDT characteristics to details of individual flow realizations, seen also in ODT, implies that model agreement can be quantified only by comparing flow ensembles, which are presently unavailable other than in an ODT run-to-run sensitivity study that is reported herein. Y1 - 2016 U6 - https://doi.org/10.1016/j.combustflame.2015.10.035 SN - 0010-2180 VL - 164 SP - 53 EP - 67 ER - TY - GEN A1 - Glawe, Christoph A1 - Schmidt, Heiko A1 - Kerstein, Alan R. A1 - Klein, Rupert T1 - XLES Part I: Introduction to Extended Large Eddy Simulation T2 - arXiv.org N2 - Direct numerical simulation (DNS), mostly used in fundamental turbulence research, is limited to low turbulent intensities due the current and future computer resources. Standard turbulence models, like RaNS (Reynolds averaged Navier-Stokes) and LES (Large Eddy Simulation), are applied to flows in engineering, but they miss small scale effects, which are frequently of importance, see e.g. the whole area of reactive flows, flows with apparent Prandtl or Schmidt number effects, or even wall bounded flows. A recent alternative to these standard approaches is the one-dimensional turbulence (ODT) model, which is limited to 1D sub-domains. In two papers we will provide a generalized filter strategy, called XLES (extended LES), including a formal theory (part I) and one special approach in the XLES family of models, called ODTLES (in part II (see Glawe et al. (2015))). ODTLES uses an ODT sub-grid model to describe all turbulent scales not represented by XLES, which leaves the larger scales to be simulated in 3D. This allows a turbulence modeling approach with a 3D resolution mainly independent of the turbulent intensity. Thus ODTLES is able to compute highly turbulent flows in domains of moderate complexity affordably and including the full range of turbulent and diffusive scales. The convergence of XLES to DNS is shown and the unconventional XLES advection approach is investigated in basic numerical tests. In part II, highly turbulent channel and duct flow results are discussed and show the future potential of XLES and ODTLES. Y1 - 2015 UR - http://arxiv.org/abs/1506.04930 ER - TY - GEN A1 - Glawe, Christoph A1 - Schmidt, Heiko A1 - Kerstein, Alan R. A1 - Klein, Rupert T1 - XLES Part II: From Extended Large Eddy Simulation to ODTLES T2 - arXiv.org N2 - In turbulence research and flow applications, turbulence models like RaNS (Reynolds averaged Navier-Stokes) models and LES (Large Eddy Simulation) are used. Both models filter the governing flow equations. Thus a scale separation approach is introduced for modeling purposes with the large scales simulated using a numerical scheme while smaller scales are assumed to be less important and might be modeled more or less easily. Unfortunately small scales are frequently of big importance, e.g. in reactive flows, wall bounded flows, or flows with significant Prandtl or Schmidt number effects. Recent alternatives to these standard models are the class of models based on the one-dimensional turbulence (ODT) idea, like ODTLES. The ability of ODT to capture highly turbulent flows (recently up to Reτ=6×105) allows ODTLES to realize 3D resolutions basically independent of the turbulent intensity. In two papers we provide a formal theory and application of an innovative modeling strategy for highly turbulent flows in domains of moderate complexity: In part I (see Glawe et al. (2015)) a new general filtering approach, called XLES (extended LES), is introduced. Contrary to LES, XLES is based on 2D filtering of the governing equations, whereby additional small scale terms are interpreted numerically. In this work a new ansatz for the ODTLES model is introduced as one special approach in the XLES family of models by incorporating the ODT model into XLES. The ODT model introduces microstructures not captured by the XLES filtered equations. To illustrate the ODTLES model capabilities, turbulent channel and duct flows up to friction Reynolds number Reτ=10000 are studied. Y1 - 2015 UR - http://arxiv.org/abs/1506.04938 ER - TY - CHAP A1 - Glawe, Christoph A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - ODTLES: A Multi-scale Ansatz for highly turbulent flows T2 - 15 The European turbulence conference, 25-28 august, 2015, Delft, The Netherland N2 - We use ODTLES, a multi-dimensional extension of the One-Dimensional-Turbulence model (ODT). ODT describes turbulent advection on a 1D sub-domain using a stochastic process for turbulent advection. These 1D sub-domains are coupled to obtain a 3D approach. ODTLES is applied to channel flow. Preliminary results for the pdf of the wall shear stress are compared to DNS. Y1 - 2015 UR - http://www.etc15.nl/proceedings/proceedings/documents/431.pdf ER - TY - CHAP A1 - Jozefik, Zoltan A1 - Kerstein, Alan R. A1 - Schmidt, Heiko T1 - Incorporation of acceleration effects into the One-dimensional-turbulence model, with application to turbulent combustion and shock-turbulence interactions T2 - 15th European Turbulence Conference 2015 August 25-28th, 2015, Delft, The Netherlands N2 - One-dimensional turbulence (ODT) is a stochastic simulation in which 3D turbulence effects are captured on a notional 1D line of sight by introducing instantaneous spatial rearrangements (maps) that represent advection by notional turbulent eddies. These eddy events incorporate the possibility of kinetic-energy changes that are equal and opposite to changes of other forms of energy such as the gravitational potential energy change due to a rearrangement of a vertical density profile. This illustrates that motion aligned with an applied force, in this case gravitation g, can be associated with energy change. Using this principle, we 1) present a model of turbulence interaction with the dilatational acceleration caused by thermal expansion in flames and show results for a turbulent counterflow flame with comparison to DNS and 2) present a model for shock-induced turbulence and show results for mixing width growth in a shock tube with comparison to experiments. Y1 - 2015 UR - http://www.etc15.nl/proceedings/proceedings/documents/356.pdf ER - TY - GEN A1 - Monson, Elizabeth I. A1 - Lignell, David O. A1 - Finney, Mark A. A1 - Jozefik, Zoltan A1 - Kerstein, Alan R. A1 - Hintze, Ryan S. T1 - Simulation of an ethylene wall fire using the spatially-evolving one-dimensional turbulence model T2 - Fire Technology, Special Issue on Validation and Fire Modeling Y1 - 2016 U6 - https://doi.org/10.1007/s10694-014-0441-2 SN - 1572-8099 VL - 52 IS - 1 SP - 176 EP - 196 ER - TY - GEN A1 - Movaghar, Amirreza A1 - Linne, Mark A1 - Oevermann, Michael A1 - Meiselbach, Falko T. A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Numerical investigation of turbulent-jet primary breakup using One-Dimensional Turbulence T2 - International Journal of Multiphase Flow N2 - Primary breakup to form droplets at liquid surfaces is an important fundamental process to study as it determines the initial properties of the dispersed phase, which affect mixing rates, secondary breakup, droplet collisions, and flow separation within the dispersed flow region. Primary breakup can be regarded as one of the least developed model components for simulating and predicting liquid jet breakup. How- ever, it is of paramount importance in many technical applications, e.g. fuel injection in engines and spray painting. This paper presents a numerical investigation of primary breakup of a turbulent liquid jet in still air at standard conditions using the one-dimensional turbulence (ODT) modeling framework. ODT is a stochastic model that simulates turbulent flow evolution along a notional 1D line of sight by applying instantaneous maps to represent the effect of individual turbulent eddies on property profiles. An important feature of ODT is the resolution of all relevant scales, both temporal and spatial. The restriction to one spatial dimension in ODT permits affordable high resolution of interfacial and single-phase property gradients, which is key to capturing the local behavior of the breakup process and allows simulations at high Reynolds and Weber numbers that are currently not accessible to direct numerical simulations (DNS). This paper summarizes our extensions of the ODT model to simulate geometrically simple jet breakup problems, including representations of Rayleigh wave breakup, turbulent breakup, and shear-driven breakup. Each jet breakup simulation consists of a short temporal channel section to initialize a turbulent velocity profile at the nozzle exit followed by an adjacent jet section. The simulations are carried out for jet exit Reynolds number of 11,500, 23,000, 46,000 and 92,000 while the Weber number is varied within the range 102–107. We present results on breakup statistics including spatial locations of droplet release, droplet sizes and liquid core length. The results on primary breakup are compared to experimental results and models. Y1 - 2017 SN - 1879-3533 VL - 89 SP - 241 EP - 254 ER - TY - GEN A1 - Lignell, David O. A1 - Lansinger, Victoria B. A1 - Medina Méndez, Juan Ali A1 - Klein, Marten A1 - Kerstein, Alan R. A1 - Schmidt, Heiko A1 - Fistler, Marco A1 - Oevermann, Michael T1 - One-dimensional turbulence modeling for cylindrical and spherical flows: model formulation and application T2 - Theoretical and Computational Fluid Dynamics N2 - The one-dimensional turbulence (ODT) model resolves a full range of time and length scales and is computationally efficient. ODT has been applied to a wide range of complex multi-scale flows, such as turbulent combustion. Previous ODT comparisons to experimental data have focused mainly on planar flows. Applications to cylindrical flows, such as round jets, have been based on rough analogies, e.g., by exploiting the fortuitous consistency of the similarity scalings of temporally developing planar jets and spatially developing round jets. To obtain a more systematic treatment, a new formulation of the ODT model in cylindrical and spherical coordinates is presented here. The model is written in terms of a geometric factor so that planar, cylindrical, and spherical configurations are represented in the same way. Temporal and spatial versions of the model are presented. A Lagrangian finite-volume implementation is used with a dynamically adaptive mesh. The adaptive mesh facilitates the implementation of cylindrical and spherical versions of the triplet map, which is used to model turbulent advection (eddy events) in the one-dimensional flow coordinate. In cylindrical and spherical coordinates, geometric stretching of the three triplet map images occurs due to the radial dependence of volume, with the stretching being strongest near the centerline. Two triplet map variants, TMA and TMB, are presented. In TMA, the three map images have the same volume, but different radial segment lengths. In TMB, the three map images have the same radial segment lengths, but different segment volumes. Cylindrical results are presented for temporal pipe flow, a spatial nonreacting jet, and a spatial nonreacting jet flame. These results compare very well to direct numerical simulation for the pipe flow, and to experimental data for the jets. The nonreacting jet treatment overpredicts velocity fluctuations near the centerline, due to the geometric stretching of the triplet maps and its effect on the eddy event rate distribution. TMB performs better than TMA. A hybrid planar-TMB (PTMB) approach is also presented, which further improves the results. TMA, TMB, and PTMB are nearly identical in the pipe flow where the key dynamics occur near the wall away from the centerline. The jet flame illustrates effects of variable density and viscosity, including dilatational effects. KW - Cylindrical ODT Y1 - 2018 U6 - https://doi.org/10.1007/s00162-018-0465-1 SN - 0935-4964 SN - 1432-2250 VL - 32 IS - 4 SP - 495 EP - 520 ER - TY - GEN A1 - Arshad, Salman A1 - Kong, Bo A1 - Kerstein, Alan R. A1 - Oevermann, Michael T1 - A strategy for large-scale scalar advection in large eddy simulations that use the linear eddy sub-grid mixing model T2 - International Journal of Numerical Methods for Heat and Fluid Flow N2 - Purpose: The purpose of this numerical work is to present and test a new approach for large-scale scalar advection (splicing) in large eddy simulations (LES) that use the linear eddy sub-grid mixing model (LEM) called the LES-LEM. Design/methodology/approach: The new splicing strategy is based on an ordered flux of spliced LEM segments. The principle is that low-flux segments have less momentum than high-flux segments and, therefore, are displaced less than high-flux segments. This strategy affects the order of both inflowing and outflowing LEM segments of an LES cell. The new splicing approach is implemented in a pressure-based fluid solver and tested by simulation of passive scalar transport in a co-flowing turbulent rectangular jet, instead of combustion simulation, to perform an isolated investigation of splicing. Comparison of the new splicing with a previous splicing approach is also done. Findings: The simulation results show that the velocity statistics and passive scalar mixing are correctly predicted using the new splicing approach for the LES-LEM. It is argued that modeling of large-scale advection in the LES-LEM via splicing is reasonable, and the new splicing approach potentially captures the physics better than the old approach. The standard LES sub-grid mixing models do not represent turbulent mixing in a proper way because they do not adequately represent molecular diffusion processes and counter gradient effects. Scalar mixing in turbulent flow consists of two different processes, i.e. turbulent mixing that increases the interface between unmixed species and molecular diffusion. It is crucial to model these two processes individually at their respective time scales. The LEM explicitly includes both of these processes and has been used successfully as a sub-grid scalar mixing model (McMurtry et al., 1992; Sone and Menon, 2003). Here, the turbulent mixing capabilities of the LES-LEM with a modified splicing treatment are examined. Originality/value: The splicing strategy proposed for the LES-LEM is original and has not been investigated before. Also, it is the first LES-LEM implementation using unstructured grids. KW - Large eddy simulations KW - LES-LEM KW - Linear eddy model KW - Passive scalar mixing KW - Splicing KW - Turbulent jet flow Y1 - 2018 U6 - https://doi.org/10.1108/HFF-09-2017-0387 SN - 0961-5539 VL - 28 IS - 10 SP - 2463 EP - 2479 ER - TY - GEN A1 - Lackmann, Tim A1 - Kerstein, Alan R. A1 - Oevermann, Michael T1 - A representative linear eddy model for simulating spray combustion in engines (RILEM) T2 - Combustion and Flame N2 - The design of new combustion concepts for low emission, high efficiency internal combustion engines often leads to combustion under low temperature conditions. Under those conditions, the assumption of fast chemistry, which has been the cornerstone of many turbulent combustion models, is not strictly valid anymore and the validity and applicability of classical combustion models such as flamelet models might be limited. In this paper we present an updated version of a recently developed regime independent modeling approach for turbulent non-premixed combustion with an emphasis on applications to internal combustion engines. The model utilizes the mode- and regime-independent linear eddy model (LEM) as a combustion and micro-mixing model in a representative way. This is achieved by time advancing only one LEM realization representing the combustion process in the whole engine domain and coupling it to a RANS simulation with a presumed β-function PDF approach for the mixture fraction. The use of LEM rather than flamelet combustion closure has several benefits, an important one being regime independence. Additionally, LEM incorporates a physically based representation of the stochastic variability of turbulent eddy motions, implying an intrinsic representation of scalar dissipation rate fluctuations. In order to capture key features of engine spray-combustion environments, the LEM methodology is extended by introducing a conical LEM domain to approximate spray spatial development, fuel vapor input based on CFD-prescribed spray evaporation, and a representation of large scale turbulent motions distinct from the inertial-range turbulence that develops at smaller scales. The representative character of LEM states is evaluated by comparing mixture fraction statistics and scalar dissipation rates generated by LEM and the CFD. The performance and predictive capability of the model for typical engine applications is evaluated by simulating a standard test case – Spray B of the Engine Combustion Network (ECN) – and comparing the results with experimental data. The results demonstrate the capability of the model to represent the spray combustion process with reasonable accuracy but also reveal some limitations. The limitations and shortcomings of the model are discussed and an outlook for further development of the approach into a regime- and mode-independent combustion model for internal engine applications is given. KW - Turbulent combustion KW - Regime independent KW - Engine simulation KW - Linear eddy model Y1 - 2018 U6 - https://doi.org/10.1016/j.combustflame.2018.02.008 SN - 0010-2180 VL - 193 SP - 1 EP - 15 ER - TY - GEN A1 - Movaghar, Amirreza A1 - Linne, Mark A1 - Herrmann, Marcus A. A1 - Kerstein, Alan R. A1 - Oevermann, Michael T1 - Modeling and numerical study of primary breakup under diesel conditions T2 - International Journal of Multiphase Flow N2 - A recently introduced stochastic model for reduced numerical simulation of primary jet breakup is evaluated by comparing model predictions to DNS results for primary jet breakup under diesel conditions. The model uses one-dimensional turbulence (ODT) to simulate liquid and gas time advancement along a lateral line of sight. This one-dimensional domain is interpreted as a Lagrangian object that is advected downstream at the jet bulk velocity, thus producing a flow state expressed as a function of streamwise and lateral location. Multiple realizations are run to gather ensemble statistics that are compared to DNS results. The model incorporates several empirical extensions of the original ODT model that represent the phenomenology governing the Weber number dependence of global jet structure. The model as previously formulated, including the assigned values of tunable parameters, is used here without modification in order to test its capability to predict various statistics of droplets generated by primary breakup. This test is enabled by the availability of DNS results that are suitable for model validation. Properties that are examined are the rate of bulk liquid mass conversion into droplets, the droplet size distribution, and the dependence of droplet velocities on droplet diameter. Quantities of greatest importance for engine modeling are found to be predicted with useful accuracy, thereby demonstrating a more detailed predictive capability by a highly reduced numerical model of primary jet breakup than has previously been achieved. KW - Spray KW - Primary breakup KW - Turbulence KW - One-dimensional turbulence KW - Direct numerical simulation (DNS) Y1 - 2018 U6 - https://doi.org/10.1016/j.ijmultiphaseflow.2017.09.002 SN - 0301-9322 VL - 98 SP - 110 EP - 119 ER - TY - GEN A1 - Lackmann, Tim A1 - Hewson, John A1 - Knaus, Robert A1 - Kerstein, Alan R. A1 - Oevermann, Michael T1 - Stochastic modeling of unsteady extinction in turbulent non-premixed combustion T2 - Proceedings of the Combustion Institute N2 - Turbulent fluctuations of the scalar dissipation rate have a major impact on extinction in non-premixed combustion. Recently, an unsteady extinction criterion has been developed (Hewson, 2013) that predicts extinction dependent on the duration and the magnitude of dissipation rate fluctuations exceeding a critical quenching value; this quantity is referred to as the dissipation impulse. The magnitude of the dissipation impulse corresponding to unsteady extinction is related to the difficulty with which a flamelet is exintguished, based on the steady-state S-curve. In this paper we evaluate this new extinction criterion for more realistic dissipation rates by evolving a stochastic Ornstein–Uhlenbeck process for the dissipation rate. A comparison between unsteady flamelet evolution using this dissipation rate and the extinction criterion exhibit good agreement. The rate of predicted extinction is examined over a range of Damköhler and Reynolds numbers and over a range of the extinction difficulty. The results suggest that the rate of extinction is proportional to the average dissipation rate and the area under the dissipation rate probability density function exceeding the steady-state quenching value. It is also inversely related to the actual probability that this steady-state quenching dissipation rate is observed and the difficulty of extinction associated with the distance between the upper and middle branches of the S-curve. KW - Extinction KW - Unsteady flames KW - Non-premixed flame KW - Scalar dissipation rate KW - Turbulence Y1 - 2016 U6 - https://doi.org/10.1016/j.proci.2016.07.014 SN - 0082-0784 VL - 36 IS - 2 SP - 1677 EP - 1684 ER - TY - GEN A1 - Klein, Marten A1 - Kerstein, Alan R. A1 - Schmidt, Heiko T1 - Stochastic modeling of transient boundary layers in high-Rayleigh-number thermal convection T2 - 25th International Congress of Theoretical and Applied Mechanics (ICTAM 20+1) N2 - One-dimensional turbulence (ODT) modeling is used to investigate the boundary layer in high-Rayleigh-number thermal convection for a notionally infinite horizontal layer of fluid. The model formulation distinguishes between turbulent advection, which is modeled by a stochastic process, and deterministic molecular diffusion to capture relevant vertical transport processes (including counter-gradient fluxes). For this study, statistical homogenization is applied to the two horizontal dimensions so that we use ODT as stand-alone tool. We show that the model yields mean and fluctuation temperature profiles that are in several respects consistent with available reference data. Furthermore, the profile of a surrogate for the fluctuation velocity is reminiscent of canonical wall turbulence. KW - one-dimensional turbulence KW - thermal convection KW - turbulent boundary layer Y1 - 2020 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Klein_2020_ODT-RBC_ICTAM20+1.pdf ER - TY - GEN A1 - Klein, Marten A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Transition to the ultimate regime in a stochastic model for thermal convection with internal sources Y1 - 2021 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Klein_poster_ipam21.pdf CY - IPAM Workshop: Transport and Mixing in Complex and Turbulent Flows (CTF2021), University of California, Los Angeles, CA, USA ER - TY - GEN A1 - Fistler, Marco A1 - Kerstein, Alan R. A1 - Wunsch, Scott A1 - Oevermann, Michael T1 - Turbulence modulation in particle-laden stationary homogeneous shear turbulence using one-dimensional turbulence T2 - Physical Review Fluids N2 - Turbulence modulation in particle-laden stationary homogeneous shear turbulence (HST) is investigated using one-dimensional turbulence (ODT), a low-dimensional stochastic flow simulation model. For this purpose, an ODT formulation previously used to study turbulence modulation in forced homogeneous isotropic turbulence (HIT) is extended, so that the model emulates the anisotropic character of HST and, potentially, anisotropic turbulence in general. This is done by limiting the kinetic-energy redistribution during an eddy event to an exchange involving two velocity components, where the three possible choices of the omitted component define three eddy types whose relative likelihoods control the anisotropy. Comparisons of ODT and direct-numerical-simulation results with reference to signatures of turbulence modulation are the basis of a broader ODT parameter study that is reported. Owing to the reduced dimensionality of ODT, it is found that the fidelity of the model for single-phase HST does not extend to particle effects on flow anisotropy, but for quantities averaged over components, parametric trends are captured. The consistent approach to case comparisons that was introduced in the HIT study to evaluate sensitivities to particle-phase parameters in a given flow configuration is extended here to a cross-comparison of HST and HIT model results, and its efficacy is again confirmed. The results provide an overall characterization of the potential for ODT to support the incorporation of particle-induced turbulence modulation into subgrid-scale closures of large-eddy simulations. Y1 - 2020 U6 - https://doi.org/10.1103/PhysRevFluids.5.124303 SN - 2469-990X VL - 5 IS - 12 ER - TY - GEN A1 - Fistler, Marco A1 - Kerstein, Alan R. A1 - Oevermann, Michael T1 - A new LES subgrid-scale approach for turbulence modulation by droplets T2 - ICLASS 14th Triennial International Conference on Liquid Atomization and Spray Systems Chicago, USA, 2018-07-21 - 2018-07-26 N2 - We present a new modelling approach for turbulence modulation by droplets on the subgrid-scale (SGS) level of Large-Eddy-Simulations (LES). Many SGS models exist for the effect of gas phase SGS on the droplet phase, but very few for the mechanisms vice versa on the turbulent intensity of the gas phase. The reasons are a lack of physical understanding and limited computational resources for extensive DNS studies. To address both problems a dimension-reduced and consequently less costly model, namely One-Dimensional- Turbulence (ODT), is used to gather information about this specific flow phenomena. ODT is a stochastic tool simulating turbulent flows along a notional 1D line of sights. For modeling the turbulent advection instantaneous maps are applied to the line which represent the effect of individual eddies on property fields and the dispersed phase. After validating the general test case of a droplet-laden shear flow against DNS data, a concept is presented on how to gather turbulence modulation for several parameter ranges in a data base and how to make them accessible on the flight for LES. The three most significant parameters, the unladen flow Reynolds number, the droplet loading and the particle momentum number, are chosen to construct an efficient data base. KW - Turbulence modulation KW - ODT KW - One-Dimensional-Turbulence KW - Particle-laden Y1 - 2018 UR - https://research.chalmers.se/en/publication/519108 ER - TY - CHAP A1 - Movaghar, Amirreza A1 - Chiodi, Robert A1 - Desjardins, Olivier A1 - Oevermann, Michael A1 - Kerstein, Alan R. T1 - A Subgrid-Scale Model for Large-Eddy Simulation of Liquid/Gas Interfaces Based on One-Dimensional Turbulence T2 - Turbulent Cascades II N2 - The interface/turbulence interaction between two fluids in a turbulent environment has an important role in many technical processes, e.g. primary liquid atomization in combustion devices. Primary atomization has a significant role in spray formation and its characteristics. The resulting dynamics typically span 4–6 orders of magnitude in length scales, making detailed numerical simulations exceedingly expensive. This motivates the need for modeling approaches based on spatial filtering such as large-eddy simulation (LES). In this paper, a new approach based on One-Dimensional turbulence (ODT) is presented to describe the subgrid interface dynamics. ODT is a stochastic model simulating turbulent flow evolution along a notional one-dimensional line of sight by applying instantaneous maps that represent the effects of individual turbulent eddies on property fields. It provides affordable high resolution of interface creation and property gradients within each phase, which are key for capturing the local behavior as well as overall trends. ODT has previously been shown to reproduce the main features of an experimentally determined regime diagram for primary jet breakup. Here a new approach called VODT is presented which produces a size-conditioned as well as a total time rate of generation of droplets for given flow conditions at an interface. At the LES level, the total droplet generation from VODT is interpreted as a rate of mass conversion of LES-resolved liquid into unresolved droplets. Preliminary results of applying VODT to a cell with a planar-shear-layer are discussed at the end of the paper. KW - combustion KW - Large eddy simulation KW - scalar dissipation Y1 - 2019 SN - 978-3-030-12547-9 SN - 978-3-030-12546-2 U6 - https://doi.org/10.1007/978-3-030-12547-9_10 SP - 83 EP - 91 PB - Springer Nature Switzerland AG CY - Schweiz ER - TY - GEN A1 - Klein, Marten A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Transition to the ultimate regime in a stochastic model for radiatively driven turbulent convection T2 - Verhandlungen der Deutschen Physikalischen Gesellschaft - BPCPPDYSOE21 KW - stochastic turbulence modeling KW - turbulent thermal convection KW - one-dimensional turbulence KW - heat transfer Y1 - 2021 UR - https://www.dpg-verhandlungen.de/year/2021/conference/bpcppdysoe/part/dy/session/2/contribution/1?lang=en ER - TY - GEN A1 - Klein, Marten A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Transition to the ultimate regime in a stochasticmodel for thermal convection with internal sources N2 - It is well established that heat transfer in turbulent Rayleigh–Bénard convection and angular momentum transfer in turbulent Taylor–Couette flow are similar in nature. This similarity manifests itself by isomorphic scaling laws for corresponding flow regimes. However, it is not clear at present if this similarity extends to flows with internal sources and different types of boundary conditions. Internal sources may occur, for example, due to radiative heating in dry or condensation in moist convection, or due to internal wave breaking and mean flow excitation in rotating Taylor–Couette-like flows. In this study, heat transfer in radiatively-driven turbulent Rayleigh–Bénard convection is investigated using the stochastic one-dimensional-turbulence model (ODT). A Boussinesq fluid of Prandtl number 1 is confined between two horizontal adiabatic no-slip walls that are located at z = 0 and H, respectively. The fluid is exposed to constant background gravity that points in vertical (−z) direction. A flow is driven by radiative heating from below yielding the local heating rate Q(z) = (P/l) exp(−z/l), where P is the prescribed mean total heat flux and l the absorption length that controls the thermal boundary layer thickness. ODT resolves all relevant scales of the flow, including molecular-diffusive scales, along a vertical one-dimensional domain, whereas stochastically sampled eddy events represent the effects of turbulent advection. ODT results reproduce and extrapolate available reference experiments of Lepot et al. (Proc. Natl. Acad. Sci. USA, 115, 2018, pp. 8937–8941) and Bouillaut et al. (J. Fluid Mech., 861, 2019, R5) in particular capturing the turbulent transition from the classical to the ‘ultimate’ regime. For these regimes, the exponent values in N u ∼ Ra^p scaling are found to be p ≈ 0.33 and p ≈ 0.55, respectively, in agreement with measured values. Joint probabilities of turbulent eddy size and location suggest that the regime transition is associated with a suppression of small-scale near-wall turbulent motions. The latter observation is found consistent with recent direct numerical simulations of heat transfer between permeable walls (Kawano et al., J. Fluid Mech., 914, 2021, A13). KW - one-dimensional turbulence KW - turbulent thermal convection KW - heat transfer KW - high Rayleigh number Y1 - 2021 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Klein_poster_ictw21.pdf UR - https://www.b-tu.de/media/video/Transition-to-the-ultimate-regime-in-a-stochastic-model-for-thermal-convection-with-internal-sources/52aa69a52b8ab3ef29cc1d8bf9f20243 UR - https://pof.tnw.utwente.nl/ictw/schedule.html ER - TY - GEN A1 - Klein, Marten A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Stochastic modeling of transient boundary layers in high-Rayleigh-number thermal convection, 25th International Congress of Theoretical and Applied Mechanics (ICTAM 20+1) N2 - One-dimensional turbulence (ODT) modeling is used to investigate the boundary layer in high-Rayleigh-number thermal convection for a notionally infinite horizontal layer of fluid. The model formulation distinguishes between turbulent advection, which is modeled by a stochastic process, and deterministic molecular diffusion to capture relevant vertical transport processes (including counter-gradient fluxes). For this study, statistical homogenization is applied to the two horizontal dimensions so that we use ODT as stand-alone tool. We show that the model yields mean and fluctuation temperature profiles that are in several respects consistent with available reference data. Furthermore, the profile of a surrogate for the fluctuation velocity is reminiscent of canonical wall turbulence. Y1 - 2021 UR - https://www-docs.b-tu.de/fg-stroemungsmodellierung/public/Klein_poster_ictam21.pdf UR - https://www.b-tu.de/media/video/Stochastic-modeling-of-transient-boundary-layers-in-high-Rayleigh-number-thermal-convection/f511d6b395472dc729543db3aa02dbc9 UR - https://www.ictam2020.org/assets/pdf/ICTAM2021-Fulllist-26-08.pdf 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 - Kerstein, Alan R. A1 - Lignell, David O. A1 - Schmidt, Heiko A1 - Starick, Tommy A1 - Wheeler, Isaac A1 - Behrang, Masoomeh T1 - Using Hips As a New Mixing Model to Study Differential Diffusion of Scalar Mixing in Turbulent Flows T2 - 2021 AIChE Annual Meeting N2 - Mixing two or more streams is ubiquitous in chemical processes and industries involving turbulent liquid or gaseous flows. Modeling turbulent mixing flows is complicated due to a wide range of time and length scales, and non-linear processes, especially when reaction is involved. On the other hand, in turbulent reacting flows, sub-grid scales need to be resolved accurately because they involve reactive and diffusive transport processes. Transported PDF methods use mixing models to capture the interaction in the sub-grid scales. Several models have been used with varying success. In this study, we present a novel model for simulation of turbulent mixing called Hierarchical Parcel Swapping (HiPS). The HiPS model is a stochastic mixing model that resolves a full range of time and length scales with the reduction in the complexity of modeling turbulent reacting flows. This model can be used as a sub-grid mixing model in PDF transport methods, as well as a standalone model. HiPS can be applied to transported scalars with variable Schmidt numbers to capture the effect of differential diffusion which is important for modeling scalars with low diffusivity like soot. We present an overview of the HiPS model, its formulation for variable Schmidt number flows, and then present results for evaluating the turbulence properties including the scalar energy spectra, the scalar dissipation rate, and Richardson dispersion. These model developments are an important step in applying HiPS to more complex flow configurations. Y1 - 2021 UR - https://plan.core-apps.com/aiche2021/event/002309c77cf108fff1a6a8a101a07ebd ER - TY - GEN A1 - Starick, Tommy A1 - Behrang, Masoomeh A1 - Lignell, David O. A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Turbulent mixing simulation using the Hierarchical Parcel Swapping (HiPS) model T2 - Proceedings of the Conference on Modelling Fluid Flow (CMFF’22) KW - differential diffusion, hierarchical parcel swapping, HiPS, mixing model, passive scalar mixing Y1 - 2022 UR - https://www.cmff.hu/papers/CMFF22_Final_Paper_PDF_96.pdf SN - 978-963-421-881-4 SP - 1 EP - 7 PB - Department of Fluid Mechanics, University of Technology and Economics CY - Budapest, Hungary ER - TY - GEN A1 - Menon, Abhilash M. A1 - Oevermann, Michael A1 - Kerstein, Alan R. T1 - A super-grid approach for LES combustion closure using the linear eddy model T2 - Combustion Theory and Modelling N2 - LES–LEM is a simulation approach for turbulent combustion in which the stochastic Linear Eddy Model (LEM) is used for sub-grid mixing and combustion closure in Large-Eddy Simulation (LES). LEM resolves, along a one-dimensional line, all spatial and temporal scales, provides on-the-fly local turbulent flame statistics, captures finite rate chemistry effects and directly incorporates turbulence-chemistry interaction. However, the approach is computationally expensive as it requires advancing an LEM-line in each LES cell. This paper introduces a novel turbulent combustion closure model for LES using LEM to address this issue. It involves coarse-graining the LES mesh to generate a coarse- level ‘super-grid’ comprised of cell-clusters. Each cell-cluster, instead of each LES cell, then contains a single LEM domain. This domain advances the combined advection–reaction–diffusion solution and also provides suitably conditioned statistics for thermochemical scalars such as species mass fractions. Local LES-filtered thermochemical states are then obtained by probability-density-function (PDF) weighted integration of binned conditionally averaged scalars, akin to standard presumed PDF approaches for reactive LES but with physics-based determination of the full thermochemical state for particular values of the conditioning variables. The proposed method is termed ‘super-grid LEM’ or ‘SG-LEM’. The paper describes LEM reaction–diffusion advancement, the LEM representation of turbulent advection, a novel splicing algorithm (a key feature of LES–LEM) formulated for the super-grid approach, a wall treatment, and a thermochemical LES closure procedure. To validate the proposed model, a pressure-based solver was developed using the OpenFOAM library and tested on a premixed ethylene flame stabilised over a backward facing step, a setup for which some DNS data is available. SG-LEM provides high resolution flame structures, temperature and mass fractions suitable for LES thermochemical closure. Additionally, it provides reaction-rate data at the coarse level, a unique feature compared to other mapping-type closure methods. Quantitative comparisons are made between the proposed model and time-averaged DNS data, focussing on velocity, temperature and species mass fraction. Results show good agreement downstream of the step. Furthermore, comparison with an equivalent Partially-Stirred Reactor (PaSR) simulation demonstrates the superior predictive capability of SG-LEM. Additionally, the paper briefly examines the sensitivity of the model to coarse-graining parameters and finally, explores computational efficiency highlighting the substantial speedup achieved when compared to the standard LES–LEM approach with potentially significant speedup relative to PaSR closure for the intensely turbulent regimes of principal interest. KW - LES KW - LEM KW - Combustion closure KW - Presumed PDFs KW - Splicing Y1 - 2023 U6 - https://doi.org/10.1080/13647830.2023.2260351 SN - 1364-7830 VL - 28 IS - 1 SP - 99 EP - 126 PB - Informa UK Limited ER - TY - JOUR A1 - Doubiani, Nidal A1 - Kerstein, Alan R. A1 - Oevermann, Michael T1 - A pressure-coupled Representative Interactive Linear Eddy Model (RILEM) for engine simulations JF - Fuel N2 - The Representative Linear Eddy Model (RILEM) was introduced by Lackmann et al. (2018) as an alternative modeling approach to simulate turbulent non-premixed combustion in engines. The model utilizes a RANS approach for turbulence and the Linear Eddy Model (LEM) with a presumed probability density function (PDF) approach for combustion closure. A distinct feature of RILEM is its potential to handle arbitrary combustion regimes and the consideration of complex physical phenomena such as differential diffusion effects. The original version of RILEM implemented a volume-based coupling between LEM and the flow solver. This work presents a new variant of RILEM, i.e., Multiple Representative Interactive Linear Eddy Model (MRILEM) based on a pressure-based coupling, to overcome some deficiencies of the original RILEM, namely statistical fidelity. Due to the introduced pressure coupling, the effects of heat losses (wall heat fluxes, latent heat of evaporation) on combustion are intrinsically included via the pressure trace. Furthermore, we introduce a new step function PDF for the progress variable defined by its mean value only. Issues with an incomplete solution space for mixture fraction and progress variable due to the stochastic nature of LEM are remedied with a PDF scaling technique, aided by a novel parameterization of the progress-variable PDF The new variant of RILEM is evaluated using part- and full-load cases of a heavy-duty metal engine. The impact of utilizing multiple LEM lines on the completeness of the solution space and its influence on the distribution of scalar values in the CFD domain was demonstrated. Results for pressure trace, flame structure, and CO emissions are analyzed and compared with simulations using the Multi-Zone Well-Mixed Model (MZWM) model and experiments. While pressure traces agree well among the different models and experiments, noteworthy differences are observed between the models regarding CO emissions and temperature. Effects of turbulence chemistry interaction were noticed when comparing MRILEM to the results of the MZWM simulation, namely flame brush and species mass fraction distribution. KW - Linear Eddy Model KW - Turbulence-chemistry interaction KW - Presumed PDF approach KW - Pollutant formation KW - Pressure coupling KW - Engine combustion Y1 - 2024 U6 - https://doi.org/10.1016/j.fuel.2023.129423 SN - 0016-2361 VL - 355 (2024) SP - 1 EP - 15 PB - Elsevier BV ER - TY - GEN A1 - Lignell, David O. A1 - Behrang, Masoomeh A1 - Kerstein, Alan R. A1 - Wheeler, Isaac A1 - Starick, Tommy A1 - Schmidt, Heiko T1 - Investigation of turbulent mixing of scalars with arbitrary Schmidt numbers using the stochastic Hierarchical Parcel Swapping Model T2 - 77th Annual Meeting of the Division of Fluid Dynamics, November 24–26, 2024; Salt Lake City, Utah N2 - Hierarchical Parcel Swapping (HiPS) is a stochastic model of turbulent mixing. HiPS is based on a binary tree structure consisting of nodes emanating from the top of the tree and terminating in parcels at the base of the tree containing fluid properties. Length scales decrease geometrically with increasing tree level, and corresponding time scales follow inertial range scaling. Turbulent mixing is modeled by swapping subtrees at different tree levels. Swaps involving single parcels result in micromixing that changes scalar states. Swaps are implemented as a Poisson process at rates corresponding to level time scales. HiPS is extended to simulation of multiple scalars with arbitrary diffusivities, considering transport in the inertial, viscous-advective, and inertial-diffusive ranges. Fundamental analysis of particle dispersion is presented with comparisons to theoretical results and DNS data in the inertial and viscous ranges. Scalar energy spectra are analysed in the three ranges and reproduce known scaling exponents. Scalar dissipation statistics are analysed and reproduce the experimental and theoretical lognormal distribution with negative skewness represented by a stretched-exponential function. DNS data are used to evaluate empirical coefficients, facilitating quantitative applications. The physical fidelity demonstrated with HiPS suggests its use as a low-cost subgrid model for coarse-grained flow simulation, for which parcel-pair mixing is a common treatment. KW - turbulent mixing KW - variable Schmidt number KW - stochastic modeling KW - hierarchical parcel swapping Y1 - 2024 UR - https://meetings.aps.org/Meeting/DFD24/Session/X39.11 PB - American Physical Society ER - TY - GEN A1 - Starick, Tommy A1 - Behrang, Masoomeh A1 - Lignell, David O. A1 - Schmidt, Heiko A1 - Kerstein, Alan R. T1 - Turbulent mixing simulation using the Hierarchical Parcel-Swapping (HiPS) model T2 - Technische Mechanik N2 - Turbulent mixing is an omnipresent phenomenon that permanently affects our everyday life. Mixing processes also plays an important role in many industrial applications. The full resolution of all relevant flow scales often poses a major challenge to the numerical simulation and requires a modeling of the small-scale effects. In transported Probability Density Function (PDF) methods, the simplified modeling of the molecular mixing is a known weak point. At this place, the Hierarchical Parcel-Swapping (HiPS) model developed by A.R. Kerstein [J. Stat. Phys. 153, 142-161 (2013)] represents a computationally efficient and novel turbulent mixing model. HiPS simulates the effects of turbulence on time-evolving, diffusive scalar fields. The interpretation of the diffusive scalar fields or a state space as a binary tree structure is an alternative approach compared to existing mixing models. The characteristic feature of HiPS is that every level of the tree corresponds to a specific length and time scale, which is based on turbulence inertial range scaling. The state variables only reside at the base of the tree and are understood as fluid parcels. The effects of turbulent advection are represented by stochastic swaps of sub-trees at rates determined by turbulent time scales associated with the sub-trees. The mixing of adjacent fluid parcels is done at rates consistent with the prevailing diffusion time scales. In this work, a standalone HiPS model formulation for the simulation of passive scalar mixing is detailed first. The generated scalar power spectra with forced turbulence shows the known scaling law of Kolmogorov turbulence. Furthermore, results for the PDF of the passive scalar, mean square displacement and scalar dissipation rate are shown and reveal a reasonable agreement with experimental findings. The described possibility to account for variable Schmidt number effects is an important next development step for the HiPS formulation. This enables the incorporation of differential diffusion, which represents an immense advantage compared to the established mixing models. Using a binary structure allows HiPS to satisfy a large number of criteria for a good mixing model. Considering the reduced order and associated computational efficiency, HiPS is an attractive mixing model, which can contribute to an improved representation of the molecular mixing in transported PDF methods. KW - differential diffusion KW - hierarchical parcel-swapping KW - HiPS KW - mixing model KW - scalar mixing Y1 - 2023 U6 - https://doi.org/10.24352/UB.OVGU-2023-044 SN - 0232-3869 VL - 43 IS - 1 SP - 49 EP - 58 ER -