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Publications HAL

titre: Generation of turbulent structures for CELES (continuous embedded LES)
auteur: Remi Manceau, Mahitosh Mehta, Martin David, Puneeth Bikkanahally
article: A turbulence day in celebration of the career of Jean-Paul Bonnet, Institute PPrime, Jun 2024, Poitiers, France
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titre: Dynamics of turbulent natural convection in a cubic cavity with centrally placed partially heated inner obstacle
auteur: Sofen Kumar Jena, Remi Manceau
article: Physics of Fluids, In press
resume: Natural convection in a cavity with a partially heated obstacle at the centre at the Rayleigh number Ra = 1.46 × 10 9 is investigated using large-eddy simulation (LES). The standard and dynamic Smagorinsky models, as well as the Wall adapting local eddy-viscosity (WALE) model, are used for the sub-grid scales, and the flow statistics are compared with recent experiments. The LES results obtained with different meshes show overall good agreement with the experiments as concerns the flow and heat transfer. Simulation with a non-ideal wall at the adiabatic side of the obstacle is also performed to explain the residual discrepancies observed in the unheated channel. Additional simulations performed with periodic conditions in the spanwise direction are very different from the full three-dimensional (3D) simulations, which demonstrates the significance of 3D effects in the cavity. In particular, periodic simulations show Tollmien-Schlichting kind waves in the transitional region, while the 3D cavity shows an early cross-flow transition to turbulence.
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titre: Grey area mitigation in hybrid RANS/LES by means of volume forcing
auteur: Mahitosh Mehta, Remi Manceau
article: THMT 2023 – 10th International Symposium on Turbulence, Heat and Mass Transfer, Sep 2023, Rome, Italy. ⟨10.1615/ichmt.thmt-23.510⟩
resume: The modeled-stress depletion is observed when the fluid flows from a RANS to a LES zone in hybrid modeling due to the dramatic decrease of the modeled stresses and the too slow increase of the resolved stresses. With the aim of developing a general remedy, independent of the type of flow, the present work develops an active approach, which consists in injecting energy in the resolved part to compensate for the loss of energy in the modelled part. Very encouraging results are obtained for channel and periodic hill flows.
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titre: Towards self-adaptivity in hybrid RANS/LES based on physical criteria
auteur: Martin David, Mahitosh Mehta, Remi Manceau
article: THMT 2023 – 10th International Symposium on Turbulence, Heat and Mass Transfer, ICHMT, Sep 2023, Rome, Italy. ⟨10.1615/thmt-23.520⟩
resume: Hybrid RANS/LES methods can produce more reliable results than RANS with a reasonable computational cost. Thus, they have the potential to become the next workhorse in the industry. However, in continuous approaches, the location of the switching between the RANS and LES modes is based on the mesh and have a significant impact on the results. The present paper aims at developing a self-adaptive strategy based on physical criteria to mitigate the influence of the user’s meshing choices on the results. The method is applied to the backward-facing step with the Hybrid Temporal LES (HTLES) model, but is applicable to any other hybrid approach. Starting from a RANS computation for initialization, successive HTLES are carried out and the mesh is refined according to the criteria. The results obtained show that the method converges and significantly improves the results when compared to RANS, with no intervention from the user. The comparison of the results with the DNS is very encouraging.
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titre: Conjugate heat transfer with different fluid-solid physical properties: a differential flux model based on elliptic blending
auteur: Jean-François Wald, Gaëtan Mangeon, Sofiane Benhamadouche, Remi Manceau, Cédric Flageul
article: THMT 2023 – 10th International Symposium on Turbulence, Heat and Mass Transfer, Sep 2023, Rome, Italy. ⟨10.1615/thmt-23.1050⟩
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titre: CFD study of thermocline formation in stratified water storage: Consideration of a second-order Boussinesq approximation to model buoyancy effects and its application to assess the impact of operating conditions
auteur: Alexis Ferre, Jérôme Pouvreau, Sylvain Serra, Remi Manceau, Arnaud Bruch
article: Proceedings of the 17th International Heat Transfer Conference, IHTC-17 14 – 18 August 2023, Cape Town, South Africa, Aug 2023, Cape Town, South Africa
resume: Thermal storages are components used in energy systems, such as district heating networks or thermal power plants, in order to decouple the supply of heat from its use. Usage rate of monophasic thermocline storages is highly dependent on the thermal gradient zone inside the fluid, also named thermocline. While thermal stratification results of a formation phase followed by a degradation phase, the early stages of thermocline establishment is primarily responsible for its thickness. CFD allow to consider the multiple physical phenomena involved during the thermocline formation, in particular the buoyancy effects. These effects are usually considered by selecting either a variable density with respect to the temperature or a constant one by using the commonly used (first-order) Boussinesq approximation. However, the former approach implies an increased computational cost, and the latter is only valid for an unclear validity range of temperature difference. Hence, this article suggests the use of a second-order Boussinesq approximation, coupled with a RANS turbulence approach, to better account for buoyancy effects in a turbulent water flow submitted to a large temperature differences. CFD results obtained with a quadratic Boussinesq approximation are similar to the one obtained with a variable density but with a computation time reduced by half. This approach is applied to the issue of reducing the thermocline thickness during its creation and the impact of linear flow rate ramps is assessed on both a uniform and initially stratified storage. On an initially cold tank, results show that the longer the ramp time, the thinner the thermocline. In contrast, on the initially stratified tank tested, a gradual injection shows no significant reduction of the thermocline thickness. This can be relevant when performing storage management enhancement.
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titre: Modélisation de la turbulence en convection naturelle (conférence introductive)
auteur: Remi Manceau
article: Journées thématiques de la SFT. Convection naturelle : aspects fondamentaux et applications, Jul 2023, Orsay, France
resume: La modélisation de la turbulence en convection naturelle est un problème à la fois difficile et important au regard des enjeux industriels et environnementaux. La flottabilité couple fortement la dynamique et la thermique et a une influence sur la plupart des termes à modéliser qui est souvent mal connue ou comprise expérimentalement. Si la modélisation au second ordre permet de prendre en compte en partie la subtilité des interactions complexes en jeu, de nombreuses questions restent ouvertes sur les échelles de temps ou la dissipation, par exemple. De nombreuses applications industrielles se basent sur des modèles à viscosité turbulente et corrigent les modèles artificiellement en diminuant le nombre de Prandtl turbulent. Une manière plus physique de procéder consiste à prendre en compte la production par la flottabilité dans la loi de comportement. Ce type de modifications, applicables aux modèles RANS et hybride RANS/LES, permettent d’améliorer la représentation de la physique dans certaines configurations non-stratifiées, mais leur influence reste marginale dans d’autre configurations. Un des problèmes non-résolus est la cohabitation de régions laminaires et turbulentes, la transition dans les couches limites en convection naturelle restant globalement un sujet complètement ouvert en modélisation.
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titre: MONACO_2025: Modelling natural convection: A Challenge for the Full Digital 2025 Ambition
auteur: Remi Manceau
article: 17th ERCOFTAC SIG15/MONACO_2025 workshop: Turbulent natural convection flows in differentially heated cavities, Jan 2023, Pau, France
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titre: Comparison of turbulence models for the case of a differentially heated square cavity
auteur: Remi Manceau
article: 17th ERCOFTAC SIG15/MONACO2025 workshop: Turbulent natural convection flows in differentially heated cavities, Jan 2023, Pau, France
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titre: Development and Validation of a new formulation of Hybrid Temporal Large-Eddy Simulation
auteur: Vladimir Duffal, Remi Manceau, Benoit de Laage de Meux
article: 17th ERCOFTAC SIG15/MONACO2025 workshop: Turbulent natural convection flows in differentially heated cavities, Jan 2023, Pau, France
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titre: Modelling turbulent flows in the natural convection regime using hybrid RANS-LES approaches
auteur: Puneeth Bikkanahally, Remi Manceau
article: 17th ERCOFTAC SIG15/MONACO2025 workshop: Turbulent natural convection flows in differentially heated cavities, Jan 2023, Pau, France
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titre: Cubic cavity with centrally placed partially heated inner obstacle: evaluation of the turbulence models
auteur: Remi Manceau
article: 17th ERCOFTAC SIG15/MONACO2025 workshop: Turbulent natural convection flows in differentially heated cavities, Jan 2023, Pau, France
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titre: An active hybrid Reynolds-Averaged Navier-Stokes/Large Eddy Simulation approach for grey area mitigation
auteur: Mahitosh Mehta, Remi Manceau, Vladimir Duffal, Benoit de Laage de Meux
article: Physics of Fluids, 2023, 35, ⟨10.1063/5.0174381⟩
resume: During the transition from the RANS (Reynolds-Averaged Navier-Stokes) mode to the LES (Large Eddy Simulation) mode, i.e., in the so-called grey area, continuous hybrid RANS/LES approaches suffer from the well-known problem of excessively slow generation of resolved structures. Indeed, when the mesh is refined in the direction of the flow, the model is designed to reduce the modeled energy, but there is no mechanism to transfer the equivalent amount of energy into the resolved motion. Hence, the total turbulent energy and turbulent stresses are underestimated, which strongly affects the prediction of the mean flow. This also constitutes a violation of the conservation of mechanical energy, which can only be corrected by an active approach, i.e., an approach that allows the injection of resolved energy. The aim of this work is to develop such an active approach based on the introduction of a fluctuating volume force into the resolved momentum equation, similar to the anisotropic linear forcing (ALF) method proposed previously. The major difference with ALF is that the new method does not require target statistics obtained by a RANS computation, but is based on a simple analysis of the rate of energy transfer related to variations in resolution, enabling the forcing to be extended to continuous hybrid RANS/LES. Application of the new method to the cases of a channel with or without periodic constriction shows a drastic improvement over the case without forcing. Although the method is applied herein to a particular hybrid RANS/LES approach (HTLES, hybrid temporal LES), it can easily be extended to any other approach, as long as a parameter identifies variations in resolution, and thus offers vast application prospects.
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titre: Numerical simulation of a turbulent natural convection flow in a cubic cavity with centrally placed partially heated inner obstacle
auteur: Sofen Kumar Jena, Puneeth Bikkanahally, Remi Manceau
article: 3rd high-fidelity industrial LES/DNS symp. (HiFiLeD), Dec 2022, Brussels, Belgium
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titre: An active hybrid RANS/LES approach for grey area mitigation
auteur: Mahitosh Mehta, Remi Manceau, Vladimir Duffal, Benoit de Laage de Meux
article: DLES13 – Direct and Large Eddy Simulation, Oct 2022, Udine, Italy
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titre: Modélisation des effets de giration pour les jets en écoulement transverse
auteur: Franck Mastrippolito, Remi Manceau, Pascal Bruel
article: Journée thématique SFT : Aérothermique des systèmes propulsifs pour l’aéronautique, Oct 2022, Paris, France
resume: Représenter l’influence de l’angle de giration entre les jets débouchant et la couche limite incidente est un défi pour la modélisation RANS de la turbulence. Le développement de méthodes basées sur la modélisation au second ordre (EB-RSM) est présenté et les résultats comparés aux données expérimentales. Des résultats préliminaires utilisant une méthode hybride RANS/LES (HTLES) sont également présentés.
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titre: Etude CFD de l’impact des conditions d’injection pour un stockage thermocline en eau
auteur: Alexis Ferré, Remi Manceau, Sylvain Serra, Jérôme Pouvreau, Arnaud Bruch
article: SFT 2022 – 30ème Congrès de la Société Française Thermique SFT, May 2022, Valenciennes, France. ⟨10.25855/T2022-046⟩
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titre: Assessment of Reynolds-Stress models for aeronautical applications
auteur: Gustave Sporschill, Flavien Billard, Michel Mallet, Remi Manceau, Hervé Bézard
article: International Journal of Heat and Fluid Flow, 2022, 96, ⟨10.1016/j.ijheatfluidflow.2022.108955⟩
resume: Three Reynolds-Stress Models (RSMs) have been benchmarked on industrial configurations with aeronautical applications. The models are first compared on a zero-pressure-gradient boundary layer, which highlights the differences in the near-wall approaches of the models. Results are then analyzed for the Skåre & Krogstad adverse-pressure-gradient boundary layer and the Common Research Model (CRM) aircraft for two Reynolds numbers. Both cases display improvements in using RSMs over the eddy-viscosity Spalart-Allmaras model. Two of the considered second-moment closures better predict the boundary layer growth and its shape factor in the Skåre & Krogstad test case, and all noticeably improve the drag-due-to-lift in the CRM case.
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titre: Development and Validation of a new formulation of Hybrid Temporal Large Eddy Simulation
auteur: Vladimir Duffal, Benoît de Laage de Meux, Remi Manceau
article: Flow, Turbulence and Combustion, 2022, 108, pp.42. ⟨10.1007/s10494-021-00264-z⟩
resume: Hybrid RANS-LES approaches have aroused interest for years since they provide unsteady information at a reduced numerical cost compared to LES. In the hybrid context, the use of temporal filtering, to control the energy partition between resolved and modeled scales, ensures a consistent bridging between RANS and LES models. In this regard, a new formulation of Hybrid Temporal Large Eddy Simulation (HTLES) is developed, aiming at improving the theoretical foundation of the model associated with an eddy-viscosity closure. The analytical development is performed, applying the Hybrid-Equivalence criterion, and the model is calibrated in decaying isotropic turbulence. In addition, an upgraded version of the approach is proposed to improve the behavior of the model in near-wall regions, introducing a two-fold shielding function and an internal consistency constraint to provide a suitable control of the RANS-to-LES transition. Applying HTLES to the k-w-SST model, the validation process is carried out on channel and periodic-hill flows, over a range of grids and Reynolds numbers. The predictive accuracy and the robustness to grid coarsening are assessed in these cases, ensuring that HTLES offers a cost-saving alternative to LES.
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titre: Large-eddy-simulation-based analysis of Reynolds-stress budgets for a round impinging jet
auteur: Arthur Colombié, Emmanuel Laroche, François Chedevergne, Remi Manceau, Florent Duchaine, Laurent Gicquel
article: Physics of Fluids, 2021, 33 (11), pp.115109. ⟨10.1063/5.0064009⟩
resume: A large-eddy simulation is used to assess the Reynolds-stress budgets of a round impinging jet in the context of a second-moment closure of turbulence. The present work focuses on the stagnation region where no data are available in the literature except in the wall vicinity. Inside the stagnation region, it is shown that the pressure terms are dominant in the budgets. They balance the Reynolds-stress production and the convective ﬂuxes. A visualization of this equilibrium through a speciﬁc indicator reveals that impingement effects extend to less than one nozzle diameter in the wall-normal direction and to about one diameter radially. This study underlines the role of the pressure diffusion term that conveys energy to the wall, balancing the high production rates (both positive or negative). Finally, the failure of turbulence models is explained by the absence of appropriate modeling of this pressure diffusion term leading to excessive Reynolds-stress values inside the impingement region.
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titre: Hybrid Temporal LES: from theory to applications
auteur: Remi Manceau, Puneeth Bikkanahally
article: HiFiLeD – 2nd High Fidelity Industrial LES/DNS Symposium, Sep 2021, Toulouse / Virtual, France
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titre: A new formulation of hybrid temporal large-eddy simulation
auteur: Vladimir Duffal, Benoît de Laage de Meux, Remi Manceau
article: ETMM 2021 – 13th International ERCOFTAC symposium on engineering, turbulence, modelling and measurements, Sep 2021, Rhodes / Virtual, Greece
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titre: Turbulence modelling improvements for APG flows on industrial configurations
auteur: Gustave Sporschill, Flavien Billard, Michel Mallet, Remi Manceau
article: 55th 3AF International Conference on Applied Aerodynamics (AERO2020+1), Mar 2021, Poitiers (Virtual), France
resume: A new version of the Spalart-Allmaras model is presented to improve adverse pressure gradient flow predictions. High fidelity numerical simulations confirmed the sensitivity of the log-law region to the pressure gradient, for both its slope and its intercept. The study is limited to the correction of the slope by tuning the von Kármán constant according to the local dimensionless pressure gradient p+ and is a first step towards better approach to account for pressure gradients. A new model is calibrated on a NACA 4412 wing at Rec = 1M section and then applied to 3D cases, including a simplified aircraft configuration. The new model displays encouraging results regarding the inner layer but exhibits limitations in the outer layer and the need for another kind of correction.
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titre: Reynolds stress RANS models for industrial aeronautical applications
auteur: Gustave Sporschill, Flavien Billard, Michel Mallet, Remi Manceau
article: WCCM-ECCOMAS Congress – 14th World Congress in Computational Mechanics and ECCOMAS Congress, Jan 2021, Paris / Virtual, France
resume: Turbulence modeling is a key feature of CFD design tools, which improvement directly impacts the design margin of aeronautical products. Second-moment Reynolds-Averaged Navier-Stokes (RANS) models, also called Reynolds Stress Models (RSM), reduce the empiricism of the Eddy Viscosity Models (EVM) and render inherently the anisotropy of turbulence for 3D and wall-bounded cases, and are therefore well-adapted to the 3D highly anisotropic flows encountered in the aeronautical applications. Their spreading in the industry has mainly suffered for a long time from numerical difficulties and a higher computational cost. Recent models have been developed with emphasis on their robustness in order to be implemented in industrial CFD codes: the elliptic blending Reynolds Stress Model (EB-RSM) [1], the SSG/LRR-ω model by the DLR [2] and the SSG-ω model by the ONERA [3]. In the present work, these RSM will be benchmarked with EVM on cases of industrial interests, including the Common Research Model used in the AIAA Drag Prediction Workshop [4] and a generic Falcon configuration. The influence of their features will be investigated, such as their near-wall models (wall-distance free elliptic blending approach vs damping functions) and the influence of their chosen length-scale. The EB-RSM uses the dissipation rate ε while the others are based on the specific dissipation rate ω, which offers better predictions in adverse pressure gradient flows but degraded boundary conditions. Preliminary results show improvement of the RSM over EVM in the pressure coefficient prediction on the CRM case, especially after the shock on the suction side of the wing, confirming the robustness of RSM and their promising benefits to aeronautical cases.
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titre: Development of a hybrid RANS-LES model based on temporal filtering for natural convection flows
auteur: Puneeth Bikkanahally, Remi Manceau, Franck Mastrippolito
article: WCCM – 14th World Congress in Computational Mechanics, ECCOMAS Congress 2020, Jan 2021, Virtual, France. ⟨10.23967/wccm-eccomas.2020.118⟩
resume: Transient, buoyancy-affected flows play a major role in some industries, for instance in the design of nuclear power plants or the under-hood space of automobiles. In order to avoid expensive experiments and promote rapid design and development, it is quintessential to employ efficient, robust, and accurate CFD models to simulate such flows. With the aim of being cost-effective and retaining the ability to capture the necessary transient phenomena, the industry standard of using RANS models alone does not suffice, whereas LES is as of yet not affordable for industrial configurations. In this context, a HybridRANS-LES model based on temporal filtering, called Hybrid Temporal Large Eddy Simulation (HTLES) is developed, thus reducing computational costs by switching to RANS in the near-wall regions while being able to predict a large part of the turbulent scales in regions where it is necessary. The present work is based on the HTLES model developed for iso-thermal configurations [1], with the hybridisation applied to the standard k-w SST model. The extension to natural convection flows is carried out using the DNS database of a differentially heated square cavity [2]. The test case is characterised by the three non-dimensional numbers viz. Rayleigh number(Ra = 10 11 ), Prandtl number (Pr = 0.71), and aspect ratio(A x = L x /L y = 1) and features a stratified core with a spatially developing buoyant boundary layer. The study reveals that the HTLES model is able to predict the mean profiles of temperature and velocity satisfactorily. Comparisons with URANS show that the HTLES model predicts the kinetic energy profiles more accurately, especially when considering coarser grids. However, it is noted that the current definition of the shielding function (used to enforce RANS close to the walls based on the Kolmogorov length scale) is inadvertently modifying the energy ratio far from the wall due to fluctuations in the dissipation rate, epsilon. This is further confirmed by way of a priori tests using the DNS database. It is essential to have a shielding function that is only effective in the near-wall regions. Therefore, to ward off this issue, a shielding function based on the Elliptic blending framework is developed. For the validation of the approach, flows in a differentially heated vertical channel [3] and a 4:1 cavity [4] are considered, in order to investigate the ability of the model to reproduce natural convection flows with very different stratification.
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titre: Asymmetric reverse transition phenomenon in internal turbulent channel flows due to temperature gradients
auteur: Sylvain Serra, Erwin Franquet, Valentin Boutrouche, Remi Manceau
article: International Journal of Thermal Sciences, 2021, 159 (106463), ⟨10.1016/j.ijthermalsci.2020.106463⟩
resume: Laminarization of a turbulent flow due to wall heating has been known for more than 50 years, to the point that it is sometimes used as means of reducing friction. However this phenomenon has been mainly studied for cylindrical pipes and with imposed heat flux but not for channel flows and with imposed temperature boundary conditions, especially with asymmetric ones (that is to say in presence of a transverse thermal gradient). Based on the recent success of some Reynolds-averaged Navier-Stokes (RANS) models to correctly describe the influence of a strong transverse temperature gradient on turbulent Poiseuille flows, when compared to similar direct numerical simulations (DNS) or large eddy simulations (LES) results, these approaches are used here to investigate reverse transition. Since the choice of turbulence model has a non-negligible influence on the results, however, it is necessary to use different models to get an indication of the uncertainty associated with them. The proposed methodology is based on the use of RANS closures that do not involve any wall functions due to the strong gradient in the wall layer that has to be modeled. Thus, two first-moment closures and a second-moment closure are considered: the k − ω − SST and the k − ε − v 2 /k, and the EB-RSM. The latter two rely on an elliptic blending. The turbulent heat flux is modeled with a simple gradient diffusion hypothesis (SGDH) and a generalized gradient diffusion hypothesis (GGDH) for the first-moment and second-moment closures respectively. In summary, more than 800 calculations are performed for the above three models in order to analyze the reverse transition, and to open room for debate on the possibility for such approaches to correctly reproduce the experimentally observed behavior.
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titre: Extension to various thermal boundary conditions of the elliptic blending model for the turbulent heat flux and the temperature variance
auteur: Gaëtan Mangeon, Sofiane Benhamadouche, Jean-François Wald, Remi Manceau
article: Journal of Fluid Mechanics, 2020, 905 (A1), pp.1-34. ⟨10.1017/jfm.2020.683⟩
resume: A new formulation of the model used in the near-wall region for the turbulent heat flux is developed, in order to extend the Elliptic Blending Differential Flux Model of Dehoux et al., Int. J. Heat Fluid Fl. (2017), to various boundary conditions for the temperature: imposed wall-temperature, imposed heat flux or Conjugate Heat Transfer (CHT). The new model is developed on a theoretical basis in order to satisfy the near-wall budget of the turbulent heat flux and, consequently, its asymptotic behavior in the vicinity of the wall, which is crucial for the correct prediction of heat transfer between the fluid and the wall. The models of the different terms are derived using Taylor series expansions and comparisons with recent direct numerical simulation data of channel flows with various boundary conditions. A priori tests show that this methodology makes it possible to drastically improve the physical representation of the wall/turbulence interaction. This new differential flux model relies on the thermal-to-mechanical timescale ratio which depends on the thermal boundary condition at the wall. The key element entering this ratio is ε θ , the dissipation rate of the temperature variance θ 2. Thus, a new near-wall model for this dissipation rate is proposed, in the framework of the second-moment closure based on the elliptic-blending strategy. The computations carried out in order to validate the new differential flux model demonstrate the very satisfactory prediction of heat transfer in the forced convection regime for all kinds of thermal boundary condition.
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titre: Modeling turbulent flows in the natural convection regime using hybrid RANS-LES approaches
auteur: Puneeth Bikkanahally, Remi Manceau
article: jspyrene2020 : Journée Scientifique autour du cluster Pyrene et autres moyens de calcul 2020, Oct 2020, Pau, France
resume: Transient, buoyancy-affected turbulent flows play a major role in many industrial and environmental applications, in particular for the sectors of the two industrial partners, automotive (PSA) and nuclear (EDF) industries. Therefore, the present PhD project focuses on configurations representative of a wide range of systems, in order to develop innovative models that will make possible the use of CFD for such very challenging configurations in the daily practice of engineers, which is not possible nowadays. The objective of the thesis is thus to incorporate buoyancy effects in a class of turbulence models, the so-called hybrid RANS/LES models, in order to provide engi neers with efficient, robust and accurate tools for the prediction of flows in the mixed or natural convection regimes. The prediction of transient phenomena due to the influence of buoyancy constitutes the main barrier that must be overcome during the thesis, with the objective of demonstrating the potential of hybrid RANS/LES models for buoyancy dominated flows.
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titre: Numerical simulations of flow and heat transfer in a wall-bounded pin matrix
auteur: Sofiane Benhamadouche, Imran Afgan, Remi Manceau
article: Flow, Turbulence and Combustion, 2020, 104 (1), pp.19-44. ⟨10.1007/s10494-019-00046-8⟩
resume: A detailed computational study was performed for the case of a wall-bounded pin-fin-array in a staggered arrangement, representative of industrial configurations designed to enhance heat transfer. In order to evaluate the level of turbulence modelling necessary to accurately reproduce the flow physics at three (3) different Reynolds numbers (3, 000, 10, 000 and 30, 000), four models were selected: two eddy-viscosity URANS models (k-ω-SST and φ-model), an Elliptic Blending Reynolds-stress model (EB-RSM) and Large Eddy Simulation (LES). Global comparisons for the pressure loss coefficients and average Nusselt numbers were performed with available experimental data which are relevant for industrial applications. Further detailed comparisons of the velocity fields, turbulence quantities and local Nusselt numbers revealed that the correct prediction of the characteristics of the flow is closely related to the ability of the turbulence model to reproduce the large-scale unsteadiness in the wake of the pins, which is at the origin of the intense mixing of momentum and heat. Eddy-viscosity-based turbulence models have difficulties to develop such an unsteadiness, in particular around the first few rows of pins, which leads to a severe underestimation of the Nusselt number. In contrast, LES and EB-RSM are able to predict the unsteady motion of the flow and heat transfer in a satisfactory manner.
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titre: Modelling of turbulent natural convection (keynote lecture)
auteur: Remi Manceau
article: 16th ERCOFTAC SIG15 Workshop on Modelling of wall bounded turbulent natural convection, Jozef Stefan Institute (IJS), Oct 2019, Ljubljana, Slovenia
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titre: A buoyancy extension for eddy-viscosity models for the natural convection regime
auteur: Syed Mohd Saad Jameel, Remi Manceau, Vincent Herbert
article: 17th European Turbulence Conference (ETC-2019), Sep 2019, Torino, Italy
resume: The influence of buoyancy on turbulent flows is significant in many industrial applications, in particular in the automotive industry. For instance, CFD is routinely used for dimensioning the underhood compartment, using commercial packages based on eddy-viscosity turbulence models. Although these models correctly reproduce the flow and heat transfer at cruising speed, they are not reliable in phases where natural convection dominates, i.e., when the car is stopped, mainly because buoyancy-turbulence interactions are not accounted for in a comprehensive manner. The objective of the present work is to introduce the mechanisms involved in this interaction in eddy-viscosity models in order to avoid the recourse to costly wind-tunnel experiments. The study is focused on simple-geometry flows for which the influence of the different physical processes can be isolated and the corresponding terms in the equations are available in DNS databases. Moreover, in order to ensure that the modifications introduced to account for buoyancy effects do not deteriorate predictions in the absence of buoyancy, the study encompasses forced, mixed and natural convection regimes, covering a range of Rayleigh numbers representative of underhood flow configurations: channel flows in forced, mixed and natural convection regimes, up to Ra = 1.7 × 107 [2] and differentially heated cavities up to Ra = 1011 [3]. Buoyancy effects are commonly introduced by adding source terms to the transport equations for the turbulent energy and the (specific) dissipation rate, in order to reproduce the influence of stratification on the dynamics of turbulence. However, this approach is ineffective in weakly stratified buoyant flows, where the temperature gradient is mainly normal to the gravity vector, as a consequence of the use of an isotropic thermal diffusivity (SGDH) to model the turbulent heat fluxes. However, the present work shows that introducing an anisotropic diffusivity (GGDH) only marginally improves the predictions. Indeed, the use of the Boussinesq constitutive relation to model the Reynolds stresses in eddy-viscosity models does not correctly represent the subtle coupling between the turbulent dynamics and the turbulent heat fluxes: the influence of buoyancy on the anisotropy of turbulence must be accounted for, in order to correctly represent the anisotropic diffusivity, which is crucial to reproduce the turbulent heat fluxes and the production mechanisms in the turbulent energy and dissipation equations. The main contribution of this work is thus the drastic improvement of the reproduction of the influence of buoyancy on turbulence in the case of weakly stratified flows in the natural convection regime, through the modification of both the turbulent heat flux model and the constitutive relation for the Reynolds stress. The former can be modeled using either an anisotropic diffusivity (GGDH) or the more sophisticate Algebraic Flux Model (AFM), and the latter is modified by introducing a buoyancy extension. The models described above have been implemented in the open-source CFD package Code_Saturne, in combination with different types of eddy-viscosity models (k-ε, k-ω, BL-v 2 /k). Detailed comparisons with DNS of the results obtained using the different hypotheses show that all the forced, mixed and natural convection regimes can be reproduced in a satisfactory manner by combining the GGDH and the buoyancy-sensitized constitutive relation (1). In particular, in natural convection, the mean velocity profiles in boundary layers close to the vertical walls are drastically improved. Detailed comparison of all the significant quantities will be presented, as well as the analysis of the influence of the different hypotheses on the reproduction of the coupling of the dynamics and heat transfer mechanisms. The results are thus very promising and this work paves the way to the improvement of CFD capabilities for the design of underhood compartment of automobiles, and, in general, for industrial configurations in which buoyancy has a significant influence.
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titre: Development and validation of a hybrid RANS/LES approach based on temporal filtering
auteur: Vladimir Duffal, Benoît de Laage de Meux, Remi Manceau
article: ASME – JSME – KSME Joint Fluids Engineering Conference 2019, Jul 2019, San Francisco, CA, United States
resume: To address the challenge of controlling the energy partition in hybrid RANS-LES methods, the use of a consistent operator based on temporal filtering is desirable. This formalism leads to the development of a consistent continuous hybrid RANS-LES approach called Hybrid Temporal LES (HTLES). In this paper, an upgraded version of HTLES is presented, focusing on improving the model for wall-bounded flows. Notably, a shielding function is integrated in the model to impose the RANS behavior in the near-wall regions. The calibration and validation of the hybrid method applied to the standard k-ω -SST model is then carried out on several test cases: decaying isotropic turbulence, channel flow and periodic-hill flow. The new version of the model fulfills the specifications: the correct subfilter dissipation; the correct migration from RANS to LES in the boundary layer; the robustness of the results to grid coarsening; the accuracy of the predictions at a reasonable computational cost.
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titre: Sensitization of eddy-viscosity models to buoyancy effects for predicting natural convection flows
auteur: Syed Mohd Saad Jameel, Remi Manceau, Vincent Herbert
article: HEFAT 2019 – 14th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Jul 2019, Wicklow, Ireland
resume: Eddy-viscosity turbulence models are sensitized to the effects of buoyancy, in order to improve the prediction in natural convection flows. The approach extends in a linear way the constitutive relations for the Reynolds stress and the turbulent heat flux, in order to account for the anisotropic influence of buoyancy. The buoyancy extension applied to two very different eddy-viscosity models lead to encouraging results for the highly challenging case of the differentially heated vertical channel.
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titre: Development and validation of a hybrid temporal LES model in the perspective of applications to internal combustion engines
auteur: Al Hassan Afailal, Jérémy Galpin, Anthony Velghe, Remi Manceau
article: Oil & Gas Science and Technology – Revue d’IFP Energies nouvelles, 2019, 74, pp.56. ⟨10.2516/ogst/2019031⟩
resume: CFD simulation tools are increasingly used nowadays to design more fuel-efficient and clean Internal Combustion Engines (ICE). Within this framework, there is a need to benefit from a turbulence model which offers the best compromise between prediction capabilities and computational cost. The Hybrid Temporal LES (HTLES) approach is here retained within the perspective of an application to ICE configurations. HTLES is a hybrid Reynolds-Averaged Navier Stokes/Large Eddy Simulation (RANS/LES) model based on a solid theoretical framework using temporal filtering. The concept is to model the near-wall region in RANS and to solve the turbulent structures in the core region if the temporal and spatial resolutions are fine enough. In this study, a dedicated sub-model called Elliptic Shielding (ES) is added to HTLES in order to ensure RANS in the near-wall region, regardless of the mesh resolution. A modification of the computation of the total kinetic energy and the dissipation rate was introduced as first adaptions of HTLES towards non-stationary ICE configurations. HTLES is a recent approach, which has not been validated in a wide range of applications. The present study intends to further validate HTLES implemented in CONVERGE code by examining three stationary test cases. The first validation consists of the periodic hill case, which is a standard benchmark case to assess hybrid turbulence models. Then, in order to come closer to real ICE simulations, i.e., with larger Reynolds numbers and coarser near-wall resolutions, the method is validated in the case of a channel flow using wall functions and in the steady flow rig case consisting in an open valve at a fixed lift. HTLES results are compared to RANS k-ω SST and wall-modeled LES σ simulations performed with the same grid and the same temporal resolution. Unlike RANS, satisfactory reproduction of the flow recirculation has been observed with HTLES in the case of periodic hills. The channel flow configuration has underlined the capability of HTLES to predict the wall friction properly. The steady flow rig shows that HTLES combines advantages of RANS and LES in one simulation. On the one hand, HTLES yields mean and rms velocities as accurate as LES since the scale-resolving simulation is triggered in the core region. On the other hand, hybrid RANS/LES at the wall provides accurate pressure drop in contrast with LES performed on the same mesh. Future work will be dedicated to the extension of HTLES to non-stationary flows with moving walls in order to be able to tackle realistic ICE flow configurations.
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titre: Hybrid temporal LES: Development and applications
auteur: Remi Manceau
article: ERCOFTAC Bulletin, 2019, Progress in RANS-based Scale-Resolving Flow Simulation Methods, 120, pp.38-42
resume: The HTLES approach, based on temporal filtering, is a formally consistent way to hybridize (U)RANS and LES. Recent advances are presented as well as applications using industrial codes, which show the strong potential of this approach for industrial CFD.
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