Hybrid temporal LES: Development and applications

International audienc

Industrial codes for CFD

MasterNumerical simulation in fluid mechanics (or CFD) has become one of the basic tools used by engineers. In this course, we will study the methods often used in industrial codes and we will give the most active research strategies which will be the future standards. This course does not aim at teaching the practical use of a CFD code, rather at providing the key knowledge to understand what the codes contain and how to use them in a wise manner.Prerequisites: For this course, it is necessary to have attended a course of introduction to turbulenceThe main tackled points are: 1. Introduction to CFD (Computational Fluid Dynamics) ◦ Different phases and important points of a simulation: geometric modelling, meshing, physical modelling, computation, post-processing, ◦ Evaluation of computational costs linked with turbulence, computer power available today and conclusions for modelling, ◦ Different existing methods (RANS, hybrid, LES, DNS) : objectives, formalism, modelling, maturity, fields of application, ◦ Global picture of CFD codes: commercial codes (Fluent, StarCD, CFX, Powerflow…), « in-house » industrial codes, open-source codes (Open-Foam, Code_Saturne). 2. Standard method used in industrial projects: RANS modelling (Reynolds-averaged Navier-Stokes modelling): ◦ Closure problem, different levels of modelling, history, ◦ Similarity with continuum mechanics (constitutive relations), physical principles, ◦ Eddy-viscosity modelling: hypotheses, selection of the constitutive relation, k-epsilon models, k-omega models, Spalart-Almaras model, etc.: limits, corrections, variations, ◦ Reynolds-stress modelling: hypotheses, advantages, limits, algebraic modelling, ◦ Wall regions: physics, joint selection of the mesh and the model, law of the wall, low-Reynolds number models, 3. More expensive methods: ◦ Large-eddy simulation (LES): filtering, subgrid-scale stresses, modelling, fields of application, ◦ Hybrid RANS/LES methods: • zonal methods: principle, interface modelling, • continuous methods: formalism, URANS, OES, VLES, SNS, DES, SBES, SAS, PANS, PITM, HTLE

Modelisation de la turbulence pour la CFD

MasterLa simulation numérique en mécanique des fluides (ou CFD) est devenue un des outils standards à disposition des ingénieurs. Dans ce cours, on dressera un état de l’art des méthodes utilisées couramment dans les codes industriels et on donnera les pistes de recherche les plus actives qui constitueront les standards de demain. Ce cours n'a pas pour objet l'apprentissage pratique de l'utilisation d'un code CFD, mais donne toutes les clés pour comprendre ce que les codes contiennent et pour les utiliser de manière éclairée.Pré-requis : Ce cours ne nécessite comme base qu'un cours d’introduction à la turbulence.Contenu :Les principaux points qui seront abordés sont les suivants :- Introduction à la CFD (Computational Fluid Dynamics)- Méthode standard dans les projets industriels : la modélisation RANS (modélisation aux moyennes de Reynolds)- Modélisation des transferts thermiques turbulent

Codes de calcul industriels pour la simulation des écoulements turbulents

MasterLa simulation numérique en mécanique des fluides (ou CFD) est devenue un des outils standards à disposition des ingénieurs. Dans ce cours, on dressera un état de l’art des méthodes utilisées couramment dans les codes industriels et on donnera les pistes de recherche les plus actives qui constitueront les standards de demain. Ce cours n'a pas pour objet l'apprentissage pratique de l'utilisation d'un code CFD, mais donne toutes les clés pour comprendre ce que les codes contiennent et pour les utiliser de manière éclairée.Pré-requis : Ce cours ne nécessite comme base qu'un cours d’introduction à la turbulence.Contenu :Les principaux points qui seront abordés sont les suivants : 1. Introduction à la CFD (Computational Fluid Dynamics) ◦ Différents phases et points durs de la simulation : modélisation géométrique, maillage, modélisation physique, calcul, post-traitement, ◦ Évaluation des coûts de calcul liés à la turbulence, puissance de calcul disponible aujourd’hui et conclusions à en tirer pour la modélisation, ◦ Différentes méthodes disponibles (RANS, hybrides, LES, DNS) : objectifs, formalisme, modélisation, maturité, champs d’application, ◦ Panorama des codes de calculs : codes commerciaux (Fluent, StarCD, CFX, Powerflow…), codes industriels « maison », codes open-source (Open-Foam, Code_Saturne). 2. Méthode standard dans les projets industriels : la modélisation RANS (modélisation aux moyennes de Reynolds) : ◦ Problème de fermeture, différents niveaux de modélisation, rapide historique, ◦ Similitude avec la mécanique des milieux continus classique (lois de comportement), principes physiques guidant la modélisation, ◦ Modélisation au premier ordre : hypothèses, choix de la loi de comportement, k-epsilon, k-oméga, Spalart-Almaras, etc. : limitations, corrections, variantes, ◦ Modèles au second ordre : hypothèses, avantages, limitations, modélisation algébrique, ◦ La région de proche paroi : difficulté physique, choix du couple maillage/modèle, lois de paroi, modèles bas-Reynolds, 3. Les méthodes plus coûteuses : ◦ La simulation des grandes échelles (LES) : formalisme de filtrage, tensions de sous-maille, modélisation, champs d’application aujourd’hui, ◦ Les méthodes hybrides RANS/LES : • méthodes zonales : principe, modélisation aux interfaces, • méthodes continues : formalisme, URANS, OES, VLES, SNS, DES, SBES, SAS, PANS, PITM, HTLE

Hybrid temporal LES: Development and applications

International audienceThe 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

Turbulence modelling for CFD

Masterumerical simulation in fluid mechanics (or CFD) has become one of the basic tools used by engineers. In this course, we will study the methods often used in industrial codes and we will give the most active research strategies which will be the future standards. This course does not aim at teaching the practical use of a CFD code, rather at providing the key knowledge to understand what the codes contain and how to use them in a wise manner.Prerequisites: For this course, it is necessary to have attended a course of introduction to turbulenceContent:- Introduction to CFD (Computational Fluid Dynamics)- Standard method used in industrial projects: RANS modelling (Reynolds-averaged Navier-Stokes modelling)- Heat transfer modellin

Progress in Hybrid Temporal LES (plenary lecture)

International audienceIn order to favour the modelling of the subgrid stresses in continuous hybrid RANS/LES methods, the comparison of the solutions with experimental or DNS databases, and eventually the understanding of the phenomenology observed in the resolved motion, defining a rigorous formalism for such methods is highly desirable. Empirical methods to bridge RANS and LES suffer from the fact that RANS and LES are based on generally inconsistent operators, statistical averaging and spatial filtering, respectively [9]. The present paper summarises recent work that tries to reconcile the two methodologies by defining consistent operators, based on temporal filtering, and provides examples of HTLES (Hybrid Temporal LES) models that can be derived based on this formalism

Toward an equivalence criterion for Hybrid RANS/LES methods

International audienceA criterion is established to assess the equivalence between hybrid RANS/LES methods, called H-equivalence, based on the modeled energy of the unresolved scales, which leads to similar low-order statistics of the resolved motion. Different equilibrium conditions are considered, and perturbation analyses about the equilibrium states are performed. The procedure is applied to demonstrate the equivalence between two particular hybrid methods, and leads to relationships between hybrid method parameters that control the partitioning of energy between the resolved and unresolved scales of motion. This equivalence is validated by numerical results obtained for the cases of plane and periodically constricted channel flows. This concept of H-equivalence makes it possible to view different hybrid methods as models for the same system of equations: as a consequence, detached-eddy simulation (DES), which is shown to be H-equivalent to the temporal partially integrated transport model (T-PITM) in inhomogeneous, stationary situations, can be interpreted as a model for the subfilter stress involved in the temporally filtered Navier–Stokes equations

Current Trends in Modeling Research for Turbulent Aerodynamic Flows

The engineering tools of choice for the computation of practical engineering flows have begun to migrate from those based on the traditional Reynolds-averaged Navier-Stokes approach to methodologies capable, in theory if not in practice, of accurately predicting some instantaneous scales of motion in the flow. The migration has largely been driven by both the success of Reynolds-averaged methods over a wide variety of flows as well as the inherent limitations of the method itself. Practitioners, emboldened by their ability to predict a wide-variety of statistically steady, equilibrium turbulent flows, have now turned their attention to flow control and non-equilibrium flows, that is, separation control. This review gives some current priorities in traditional Reynolds-averaged modeling research as well as some methodologies being applied to a new class of turbulent flow control problems

Development and validation of a hybrid temporal LES model in the perspective of applications to internal combustion engines

International audienceCFD 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