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Storms deepen the mixed layer, entrain nutrients from the pycnocline, and fuel phytoplankton blooms in midlatitude oceans. However, the effects of oceanic submesoscale (0.1-10 km horizontal scale) physical heterogeneity on the physical-biogeochemical response to a storm are not well understood. Here, we explore these effects numerically in a Biogeochemical Large Eddy Simulation (BLES), where a four-component biogeochemical model is coupled with a physical model that resolves some submesoscales and some smaller turbulent scales (2 km to 2 m) in an idealized storm forcing scenario. Results are obtained via comparisons to BLES in smaller domains that do not resolve submesoscales and to one-dimensional column simulations with the same biogeochemical model, initial conditions, and boundary conditions but parameterized turbulence and submesoscales. These comparisons show different behaviors during and shortly after the storm. During the storm, resolved submesoscales double the vertical nutrient flux. The vertical diffusivity is increased by a factor of 10 near the mixed layer base, and the mixing-induced increase in potential energy is double. Resolved submesoscales also enhance horizontal nutrient and phytoplankton variance by a factor of 10. After the storm, resolved submesoscales maintain higher nutrient and phytoplankton variance within the mixed layer. However, submesoscales reduce net vertical nutrient fluxes by 50% and nearly shut off the turbulent diffusivity. Over the whole scenario, resolved submesoscales double storm-driven biological production. Current parameterizations of submesoscales and turbulence fail to capture both the enhanced nutrient flux during the storm and the enhanced biological production. Key Points Physical/biogeochemical large eddy simulations show that submesoscales enhance turbulent mixing and net community production during a storm Submesoscales suppress mixed-layer turbulence after the storm and facilitate the formation of vertical gradients of phytoplankton Ocean models with grid spacings

Il presente studio è incentrato sulla valutazione delle performance e sviluppo della scia di una turbina marina soggetta a condizioni di stratificazione stabile. Lo studio numerico è stato condotto per mezzo della tecnica di ‘Large Eddy Simulation’ (LES) mediante l’utilizzo del modello LES-COAST, sviluppato dal gruppo di ricerca. Il modello numerico è stato validato attraverso la comparazione tra i risultati numerici e dati di laboratorio(reperiti in letteratura) riguardanti la potenza estratta e la forza di thrust generata dalla turbina. Data l’importanza della stratificazione nelle dinamiche marine, l’ obbiettivo è studiare l’interazione tra la stratificazione e il campo della turbina. Inoltre la produzione globale di un parco di turbine marine e la produzione delle singole turbine possono essere influenzati dagli effetti della stratificazione sul campo di moto. Per quanto riguarda la letteratura, non sono state individuate ricerche con lo scopo di studiare gli effetti della stratificazione sullo sviluppo della scia e della produzione di energia della turbina. I siti di marea nei quali le turbine vengono istallate possono essere soggetti alla presenza di stratificazione stabile di densità. La stratificazione di densità è causata da variazioni di temperatura e/o salinità tra le acque superficiali e le acque del fondo marino. Allo scopo di valutare gli effetti della stratificazione sulla produzione di energia e sul recupero del deficit di velocità, sono stati simulati due tipi di stratificazione stabile: una condizione intensa e una condizione debole. La stratificazione di tipo debole è stata simulata imponendo un salto di temperatura in modo da ottenere un profilo di densità a forma di gradino. Per quanto riguarda la stratificazione intensa, è stato imposto un salto di salinità, anche in questo caso a forma di gradino, il quale produce una maggiore variazione di densità rispetto al caso debole. Successivamente la turbina è stata introdotta all’interno dei due campi stratificati e i conseguenti risultati sono stati comparati. L’analisi dei risultati dimostra che la stratificazione ha un impatto sulla produzione di energia della turbina e sull’evoluzione e recupero della scia. Inoltre l’effetto di mescolamento causato dalla turbina è stato analizzato The present study concerns the evaluation of the effects of stable stratified condition on turbine performance and wake development. The numerical analysis has been carried out by means of Large Eddy simulation (LES) through the in-house LES-COAST model coupled with a turbine module that computes the turbine induced forces. The capability of the model in reproducing power and thrust characteristics of a turbine has been proved from the comparison between the numerical results and the experimental data supplied by literature. Since the stratification is an important factor in the marine dynamics, the aim is to evaluate the interaction between the stratification and the turbine. Moreover the overall power production of a tidal farm and the power output of the single turbines can be influenced by the effects that stratification entails on the flow field. To the best of our knowledge, in the marine field there is no research aimed at studying the influence of marine stratification on wake recover and turbine performance. Tidal sites where marine turbines are installed can be subject to the presence of density stable stratified conditions. The density stratification is due to temperature and/or salinity variations between the superficial and the bottom water. In order to evaluate the influence of stratification on power output and wake development and recover, we simulated to types of stable stratified condition: a weak and a strong stratification. The weak stratification has been simulated imposing a temperature jump in order to obtain a vertical density profile with a step shape. For the strong stratification, we imposed a salinity jump with a step shape which gives rise to an higher density variation compared to the weak case. Then the turbine has been introduced into the stratified fields and the results have been compared. The analysis of the results highlights that the stratification has an impact on turbine production and on wake development and recover. Moreover the turbine mixing effect is analyzed.

High-cycle thermal fatigue due to turbulent mixing of streams at distinct temperatures is an interdisciplinary issue affecting safety and life extension of existing reactors together with the design of new reactors. It is challenging to model damage and thermal loads arising from the above mixing. In order to collect vast data sets for the validation of codes modeling turbulent thermal mixing under reactor conditions, temperatures were sampled at the inner surface of the vertical annular volume between two concentric 316LN stainless steel tubes. This annulus simplifies that between control-rod guide tube and stem in Swedish boiling water reactors (BWRs) Oskarshamn 3 and Forsmark 3. In 2008, several stems there were reported as broken or cracked from thermal fatigue. Cold water entered the annulus at 333 K, at axial level z = 0.15 m. It moved upward and mixed with hot water, which entered the annulus at 549 K, at z = 0.80 m. Pressure read 7.2 MPa. Hot and cold inlet temperatures and pressure match BWR conditions. The thermocouples attached to the inner tube could only acquire inner-surface temperatures at six locations, so the inner tube was translated and rotated about the z-axis to expand the measurement zone. Mixing inhomogeneity was estimated from such measurements. In the cases examined, the inner-surface temperatures from areas with the highest mixing inhomogeneity show dominant frequencies lower than ten times the inverse of the experiment time. The uncertainty of this temperature measurement appears to be equal to 1.58 K. A large eddy simulation (LES) of mixing in the above annulus was conducted. Experimental boundary conditions were applied. The conjugate heat transfer between water and tubes was modeled. The wall-adapting local eddy viscosity (WALE) subgrid model was adopted. A finite element analysis (FEA) of the inner tube was performed using LES pressure and temperature as loads. Cumulative fatigue usage factors (CUFs) were estimated from FEA stress histories. To this end, the rainflow cycle-counting technique was applied. CUFs are highest between z = 0.65 m and z = 0.67 m. Cracking is predicted to initiate after 97 h. LES and experimental inner-surface temperatures agree reasonably well in relation to mean values, ranges, mixing inhomogeneity, and critical oscillation modes in areas sensitive to fatigue. LES inner-surface temperatures from areas with the highest CUFs show dominant frequencies lower than ten times the inverse of the simulation time. A robust, effective iterative algorithm for reconstructing the transient temperature field in the inner tube from redundant boundary data was implemented and verified. Temperature-dependent properties were included. Initial conditions and over-specified boundary data in the inverse problem were perturbed with Gaussian noise to check the robustness of the solving method to noise. Termisk högcykelutmattning på grund av turbulent blandning av flöden av olika temperaturer är en tvärvetenskaplig fråga som har bäring på säkerhet, underhåll och livstidsförlängning av kärnkraftverk i drift tillsammans med utvecklingen av nya reaktorer. Det är utmanande att modellera delskador och termiska belastningar som härrör från denna blandning. För att samla stora datamängder för validering av koder modellerande turbulent termisk blandning vid reaktordriftförhållanden, mättes temperaturer vid den inre ytan av den vertikala annulära (ringformade) kanalen mellan två koncentriska rör i 316LN rostfritt stål. Denna annulära kanal representerar den verkliga geometrin mellan styrstavsledrör och styrstavsförlängare i svenska kokvattenreaktorer (BWR) Oskarshamn 3 och Forsmark 3. Vid dessa reaktorer uppvisade ett antal styrstavsförlängare sprickbildning till följd av termisk utmattning under år 2008. I den annulära kanalen strömmade kallare vattenflöden vid 333 K, vid axiell nivå z = 0.15 m. Flödena rörde sig uppåt och blandades med varmare vattenflöden, vilka strömmade i den annulära kanalen vid 549 K, vid z = 0.80 m. Trycket sattes till 7.2 MPa. 333 K, 549 K och 7.2 MPa överensstämmer med BWR-förhållanden. Termoelement fastlödda vid det inre röret kunde endast mäta innerytans temperatur på sex platser. För att kunna mäta temperaturen i hela blandningsområdet kunde röret roteras från 0° till 360° och förflyttas vertikalt över en sträcka av 387 mm. Blandningsinhomogenitet uppskattades från sådana mätningar. I de undersökta fallen visar innerytans temperatur från områden där blandningen är som minst homogen dominerande frekvenser som är lägre än tio gånger inversen till experimenttiden. Osäkerheten i dessa temperaturmätningar visar sig vara 1.58 K. En storvirvelsimulering (LES) av blandning i den annulära kanalen utfördes. Experimentella randvillkor applicerades. Den konjugerade värmeöverföringen mellan vatten och rör modellerades. De små virvlarna (oupplösta skalor) approximerades med hjälp av en turbulensmodell kallad WALE, som ger rätt asymptotiskt beteende för turbulent viskositet nära väggen. En finitelementanalys (FEA) av det inre röret utfördes med LES-tryck och temperatur som belastningar. Totala delskador uppskattades från FEA-spänning/tid kurvor. För detta ändamål applicerades regndroppsmetoden. De totala delskadorna når sina högsta värden mellan z = 0.65 m och z = 0.67 m. Sprickinitiering förväntas inträffa efter 97 timmar. Innerytans CFD-temperatur är i en rimlig överensstämmelse med experimentella data med avseende på medelvärde, omfång, blandningsinhomogenitet och kritiska svängande modalfunktioner som utgör temperaturtidsserier i områden som är utsatta för utmattning. Innerytans CFD-temperatur från områden med högsta totala delskador visar dominerande frekvenser som är lägre än tio gånger inversen till simuleringstiden. En robust, effektiv, iterativ algoritm för att beräkna det transienta temperaturfältet i det inre röret utifrån överflödiga randdata implementerades och verifierades. Temperaturberoende egenskaper inkluderades. Initiala förhållanden och överflödiga randdata i det inversa problemet stördes av gaussiskt brus för att undersöka lösningsmetodens robusthet mot brus. QC 20181022

At present only the characteristics of a forest stand and its immediate environment are taken into account in calculating forest wind risk. However, it is known that the wind is strongly affected by the surfaces over which it has previously flowed. Forest edges in particular play an important role in determining the characteristics of the atmospheric flow by generating increased turbulence, triggering the formation of coherent tree scale structures. In a fragmented landscape, consisting of surfaces of different heights and roughness, the multiplicity of edges may have cumulative effects at the regional scale leading to increased forest damage during storms. Flow changes in the atmospheric boundary-layer across surface roughness changes have received extensive study in the past because of their importance in determining velocities, turbulence levels and exchange between the atmosphere and biosphere or ground. There have also been a number of studies across single forest edges both in the field, wind-tunnels and computer models. However, there have been no studies of flow across multiple forest edges or the impact of forest fragmentation on the characteristics of the boundary-layer. The only studies on multiple surface changes have been wind-tunnel examination of the flow though and across multiple wind-breaks. In this thesis we show results from a series of wind tunnel experiments on a range of levels of forest fragmentation. Five gap spacings (L = ~ 5, ~ 10, ~15, ~20, ~30h, where L is the length of the gap and h is the canopy height) were investigated using 3D laser doppler velocimetry in order to assess the effects of fragmented landscapes on mean and turbulent wind characteristics. The fragmentation was two-dimensional with the transition between forest and gaps only being along the wind direction and the forest and gaps were continuous perpendicular to the wind direction. The wind speeds and turbulence characteristics are compared against measurements from a single forest edge in the wind tunnel, which acts as a reference. No enhancement of turbulence formation at a particular level of fragmentation was observed but there was a consistent pattern of wind speed and turbulence back from the first edge of each simulation with the horizontal velocity at tree top increasing and the turbulent kinetic energy decreasing as gap size increased. We also compare mean wind speeds (U and W) and turbulence characteristics (variance in u, v, and w; skewness in U, V, and W; Reynold’s stress, and TKE) at all points in the experimental measurement domain of the wind tunnel with Large Eddy Simulation (LES) results, which allows us to confirm the validity of the LES calculations and to conduct a wider range of experiments than was possible in the wind-tunnel. The results demonstrate the importance of the frontal area index or roughness density of elements (in this case trees) in determining the nature of the flow and the effective roughness of the overall surface. They also show that as the gaps between forest blocks increases the flow transitions (at a gap size between 10 to 15 tree heights) from flow comparable to that over a continuous forest to flow across a set of isolated forest blocks., A l’heure actuelle, seuls des facteurs locaux, stationnels, sont considérés pour le calcul des risques liés au vent alors que le vent qui aborde un peuplement forestier est affecté par les surfaces sur lesquelles il vient de passer ; les lisières en particulier jouent un rôle important sur l’écoulement atmosphérique, en contribuant à générer de la turbulence. Dans un paysage fragmenté, constitué d’une mosaïque de surfaces de différentes hauteurs et rugosités, la multiplicité des lisières est ainsi susceptible d’avoir des effets cumulatifs perceptibles à l’échelle régionale, qui pourraient contribuer de manière significative à la fragilité des massifs face à des tempêtes. Certains niveaux de fragmentation semblent susceptibles de conduire à un accroissement des risques en cas de vent violent. Bien que la région de lisière a été étudiée de manière approfondie dans le passé en raison de leur importance pour la détermination des vitesses de vent, des niveaux de turbulence et des échanges entre l’atmosphère et la canopée, il n’y a aucune étude de l’impact de lisières multiples ou de la fragmentation des forêts sur les caractéristiques de la couche limite à l’échelle du paysage. Quelques rares études laissent penser que la fragmentation du paysage pourrait moduler de manière significative la structure turbulente de la couche limite atmosphérique mais ces études concernent des réseaux de brisevents plutôt qu’un ensemble de parcelles forestières. On cherche par conséquent à caractériser les champs de vent et de turbulence pour ces différentes configurations. Pour ce faire, une expérimentation en soufflerie à été réalisée, visant à caractériser l’écoulement sur des maquettes de paysage présentant cinq degrés de fragmentation (L = ~ 5, ~ 10, ~15, ~20, ~30h, où L est la distance entre deux patchs de forêts régulièrement espacés et h est la hauteur de la canopée). Un cas homogène a également été simulé et sert ici de référence. Pour le modèle de canopée choisi, ces expérimentations montrent que l’énergie cinétique turbulente présente dans la basse atmosphère ne passe pas par un maximum pour une valeur de l’espacement intermédiaire comme il était supposé à l’origine. Le cas homogène est la configuration la plus rugueuse. Pour de grands espacements l’influence d’une parcelle ne se fait guère sentir sur la suivante et lorsqu’ils sont faibles l’écoulement ne "ressent" guère les clairières et présente des caractéristiques semblables au cas homogène. Nous avons également évalué un modèle atmosphérique de type "simulation des grandes échelles" à l’aide des données présentées précédemment. Le modèle est capable de reproduire les grandes caractéristiques de la turbulence telles que les vitesses de vent horizontales et verticales, l’énergie cinétique turbulente, les contraintes de Reynolds et les coefficients d’asymétrie horizontale et verticale en tous points du domaine. Cela nous a permis de confirmer la validité des calculs numériques et de simuler l’écoulement sur une plus large gamme de paysages fragmentés. Les résultats démontrent l’importance de l’indice foliaire pour le calcul de la rugosité effective sur une succession de patchs de forêt.

Seit Mitte des letzten Jahrhunderts hat sich der Gedanke etabliert, dass der gravitative Kollaps von Molekülwolken durch Erhaltung des in ihnen vorhanden Drehimpulses zur Bildung einer scheibenartigen Struktur und damit u.a. zum Geburtsort unseres Sonnensystems führt. Dieser Entstehungsprozess ist einer ganzen Reihe von Objekten gemein und kann auf den unterschiedlichsten Größenskalen erfolgen. Das eigentliche Problem ist die Umverteilung des Drehimpulses, ohne die es keine Entwicklung zu beispielsweise einem Hauptreihenstern geben kann. Das Aufsammeln von Material durch das Zentralobjekt wird als Akkretion bezeichnet. Der Mechanismus der Akkretion spielt in der Astrophysik eine entscheidende Rolle, da die Akkretionsscheibe ebenfalls den "Motor" der aktiven galaktischen Kerne bildet. Durch innere Reibung wird Gravitationsenergie sehr effizient dissipiert, so dass sie zu den leuchtkräftigsten Objekten im Universum gehören. Sie spielen damit eine entscheidende Rolle in der Entstehung von Galaxien und haben somit auch einen Einfluss auf die kosmologische Entwicklung. Der Fakt, dass wir diese Objekte beobachten können, bedeutet, dass sie sich mindestens auf Zeitskalen kleiner als das Weltalter entwickelt haben müssen, was eine durch molekulare Prozesse vermittelte innere Reibung (Viskosität) ausschließt. Die Effekte wären um viele Größenordnungen zu gering, weshalb seit langem Konsens darüber besteht, dass eine durch Turbulenz hervorgerufene Viskosität erforderlich ist. In dieser Arbeit wird sich dieser Problematik dahingehend genähert, dass die seit einigen Jahrzehnten etablierten sehr einfachen Parametrisierungen einer turbulenten Viskosität durch eine allgemeinere Theorie, die auf die jeweils vorherrschende Strömungsgegebenheit Rücksicht nimmt, zu ersetzen. Hierbei wird die Methode der Large Eddy Simulation (LES) verwendet, die große Verbreitung in der Meteorologie und den Ingenieurwissenschaften gefunden hat und ebenfalls zunehmend bei astrophysikalischen Fragestellungen eingesetzt wird. Obwohl die darin enthaltenen Methoden ebenfalls heuristischer Natur sind, haben sie den Vorteil, dass sie einerseits durch Vergleich mit Experimenten ihre Daseinsberechtigung untermauern können und zweitens an die tatsächlich in der Simulation auftretende Turbulenz rückkoppeln. Für die Untersuchung werden Akkretionsscheiben mit und ohne dominantes Scheibenpotential jeweils im klassischen Ansatz und mit der LES durchgeführt. Die ansonsten identischen Modelle werden eingehend analysiert. Es zeigt sich dabei, dass die auftretenden Akkretionsraten teilweise starke Ähnlichkeiten aufweisen und ebenfalls zu einem annähernd gleichen Massenwachstum des Zentralobjektes führen. Um den Nachteil von zweidimensionalen Modellen wett zu machen, werden ebenfalls rotationssymmetrische und flache Modelle untereinander verglichen. Auch hier zeigt sich tendenziell ein ähnliches Verhalten, was als Rechtfertigung für den Ansatz verstanden werden kann. Bei den flachen Modellen treten verstärkt nicht achsensymmetrische Instabilitäten auf, die das gesamte Verhalten der Scheibe stark beeinflussen. Since the middle of last century, the idea has been established that the gravitational collapse of molecular clouds results in a disk-like structure due to conservation of angular momentum. This process occurs on very different length scales and is applicable to a variety of astrophysical objects from the formation of our solar system to the evolution of black holes in galaxy centers. The fundamental problem is the redistribution of angular momentum which is a necessary condition for the evolution of the central object. The collecting of material through the central object is called accretion. It is believed that accretion discs are the engines of active galactic nuclei (AGN), which play a major role for galaxy formation and therefore have an impact on cosmological evolution. Due to viscosity gravitational energy is dissipated very effectively so that they are among the most luminous objects in the universe. The fact that we can observe these objects means that they must have evolved at least on time scales less than the age of the universe. Therefore molecular viscosity as source for energy dissipation is ruled out because the expected time scales are orders of magnitudes too large. This is the reason why there is a broad consensus that turbulence is the only way to explain the short time scales. This thesis approaches the problem by replacing the rather simple but well established methods with a more general theory of turbulence modeling. This type of simulation is called large eddy simulation (LES) and has been used in meteorology and engineering sciences for decades. Although these methods are also based on heuristic assumptions, they are far more general and allow for comparison with laboratory experiments. In addition, they connect directly to the turbulent motion generated by the simulation. Simulations of accretion disks with and without self-gravity are performed and compared to the classic parameterization. The otherwise identical models are analyzed in detail. The achievable accretion rates and the evolution time scales of the central objects are of the same order compared to results obtained with the classic parameterization. To compensate for the drawback of two-dimensional models, rotationally symmetric and flat models are compared with each other. Both show similar behavior, which can be regarded as an indirect justification of the approach. In the flat models non-axisymmetric instabilities occur that affect the overall behavior of the disc strongly.

[EN] The present study gives a general outline for the fluid-dynamical calculation of flows at high pressure conditions. The main idea is to present a mathematical description of high pressure processes in liquids at compressible conditions, quantifying the effect of density variations on the flow pattern due to those pressure variations. The improved mathematical approach is coupled to a Large Eddy Simulation (LES) solver. The main code was developed by OpenSource Ltd. for OpenFOAM, and the authors have introduced the additional expressions in order to calculate particular variables. For validating the code improvement, the LES solver is applied to a modern common-rail nozzle injector used in diesel engines. Results have been compared against other calculations that assumed constant properties and simultaneously validated with experimental data. © 2010 Elsevier Ltd., This work has been funded by MINISTERIO DE CIENCIA E INNOVACION from Spain, in the framework of the project “ESTUDIO TEORICO EXPERIMENTAL DE LA INFLUENCIA DEL COMBUSTIBLE SOBRE LA CAVITACION Y EL DESARROLLO DEL CHORRO EVAPORATIVO”, Reference No. TRA2010-17564. The authors would like to thank Universidad de Valencia for the computer resources, technical expertise, the assistance provided and for allowing the use of the supercomputer Tirant.

This paper describes the simulation of adiabatic gas-liquid flow based on the Eulerian approach. An adequate characterization of the momentum exchange between the phases is necessary. The basic experiment investigating the momentum exchange is vertical upward flow in a pipe. This paper describes the main computational fluid dynamics (CFD) approaches for momentum exchange and the comparison to experimental results for several test conditions. For large gas-injection rates, a bubble size distribution including bubble coalescence and fragmentation has to be considered. The paper describes the concept of the inhomogeneous multiple size group model MUSIG, developed by ANSYS/CFX and Helmholtz-Zentrum Dresden-Rossendorf (HZDR), which is implemented in the CFD-code CFX, and a comparable concept of a population balance model implemented in NEPTUNE CFD [Commissariat a l'Energie Atomique (CEA), É lectricité de France (EDF), Institut de Radiopro-tection et de Sûreté Nucléaire (IRSN) and AREVA]. Measurements performed at HZDR are used for model validation. Crucial for the quality of the models described are the base approaches for bubble coalescence and fragmentation. Among other influences, these phenomena depend on the level of liquid turbulence. Therefore special attention was devoted to CFD simulation of bubbly turbulent flow based on different model concepts. Concepts based on Reynolds-averaged turbulence models are described. At the Paul Scherrer Institute, large eddy based studies were performed and compared to DEDALE experiments. The work was performed within the NURESIM and NURISP projects under the 6th and 7th European Framework Program. © 2011 by Begell House, Inc.

The combination of Geostrophic forcing and an ABL height of O(1000 m) in the atmospheric boundary layer (ABL) leads to a Reynolds number (Re) of O(10^8). Re's of this magnitude indicate turbulence with an excessive number of scales of motion, or degrees of freedom. The computational power required for explicit representation of all scales (to the Kolmogorov scale) in such flows is far beyond that which is currently available (even when massively parallel computing facilities are employed); from this, the method of large-eddy simulation has emerged. In this methodology, a filtering operation separates the scales of motion into resolved- (R-) and subgrid-scale (SG-S) motions. The R-S motions are typically large and anisotropic (owing to their interaction with the boundary conditions), whilst the SG-S motions are small. The R-S motions are solved explicitly using the filtered Navier-Stokes (N-S) equations -- SG-S motions are parameterized. Parameterization of the SG-S fluid motions has been, and remains, the topic of a considerable research effort. A new SG-S model is presented, namely the LDTKE model (dynamic point-to-point computation of SG-S turbulent kinetic energy with a 1-equation model). 1-equation refers to a prognostic equation for TKE (Turbulent Kinetic Energy). The model is applied to LES of the neutrally buoyant ABL. Many highly sophisticated dynamic (tuning-free) SG-S models have recently been developed, however we still observe adhoc averagaing/clipping. TKE-based SG-S parameterizations have been extensively used, although often they're based on constant coefficients -- the varaint presented here combines a completely dynamic modeling procedure with point-to-point computations. The only constraints imposed on LDTKE is that the eddy-viscosity may not be negative (attempts to include TKE backscatter in LDTKE caused numerical instabilities).

We review a few recent investigations concerning LES (Large Eddy Simulation), OES (Organised Eddy Simulation), and Statistical Modelling works with two-equation RANS models aiming at preparing short term improvement of industrial tools for a good representation of separated, unsteady flows, involving vortex shedding. A focus will be proposed on OES modelling and on the use of wall laws. Examples will concern vortex shedding behind cylinders and airfoils, dynamic stall of multi-body airfoil. This paper is dedicated to Pierre Perrier at the occasion of the NFD2000 symposium organised in his honour.

Our contribution consists of the demonstration of the advantages of LES-WALE coupled with PDF approach including progress variable (c) in reacting flow, by using the Fluent-CFD. The confirmation is based on the comparison of three parameters: mean longitudinal velocity, intensity of longitudinal velocity and lengths of recirculations zones. In line with what was observed by the experimental reference study, the simulation succeeds to detect the flame zone of the recirculating region and shows the differences between the different cases of flows in variable equivalence ratio (Φ=0.60 and 0.75) or in variable mass flow rate (Q= 65 and 195 g/s). All cases of study considered the identical conditions from the tow supply channels of the burner. The main issue is the modeling of the closure of the turbulent combustion. In addition, the numerical simulation predicts as well as the asymmetry and the symmetry flow, respectively, for inert and reacting flows.