Approximate Wall Boundary Conditions for Large Eddy Simulations

This paper provides a discussion of several aspects of the construction of approaches that combine statistical (Reynolds-averaged Navier-Stokes, RANS) models with large eddy simulation (LES), with the objective of making LES an economically viable method for predicting complex, high Reynolds number turbulent flows. The first part provides a review of alternative approaches, highlighting their rationale and major elements. Next, two particular methods are introduced in greater detail: one based on coupling near-wall RANS models to the outer LES domain on a single contiguous mesh, and the other involving the application of the RANS and LES procedures on separate zones, the former confined to a thin near-wall layer. Examples for their performance are included for channel flow and, in the case of the zonal strategy, for three separated flows. Finally, a discussion of prospects is given, as viewed from the writer's perspective.

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“…Werner & Wengle 1991;Hoffman & Benocci 1995;Temmerman et al 2003). These can provide useful approximations in near-equilibrium conditions, e.g.…”

Section: Brief Review Of Combined Les-rans Methodologiesmentioning

confidence: 99%

Simulating flow separation from continuous surfaces: routes to overcoming the Reynolds number barrier

Leschziner

Tessicini

2009

Phil. Trans. R. Soc. A.

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“…By neglecting the convective terms in (1.7), Hoffman and Benocci (1995) constructed a local model by integrating the TBLE in the wall-normal direction:…”

Section: Two-layer Wall Modelsmentioning

confidence: 99%

“…Since this was the same approach taken by Hoffman and Benocci (1995), but without neglecting non-linear terms, it was unclear what physics the near-wall model should retain and what could be neglected. Cabot (1996) considered a variety of different near-wall models in an LES of a backward facing step flow.…”

Section: Chapter 1 Introductionmentioning

confidence: 99%

Wall Models for Large-Eddy Simulation Based on Optimal Control Theory

Moin¹,

Templeton²,

Wang³

2006

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Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Washington Headquarters Service, Directorate for Information Operations and Reports, Paperwork Reduction Project (0704-0188) Washington DC 20503 PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 14. ABSTRACT Large-eddy simulation (LES) requires very high resolution in high Reynolds number, attached turbulent boundary layers due to the need to capture the small, dynamically important near-wall eddies. Wall modeling enables LES to be performed on grids that do not resolve these eddies by providing approximate boundary conditions to the simulation. Unfortunately, wall models based on purely physical reasoning often lead to an inaccurate LES, particularly on coarse grids and at high Reynolds numbers, because they do not account for numerical and subgrid scale modeling errors. To compensate for these errors, a wall model based on optimal control theory has been developed that differs from previous approaches in two significant ways. First, the computational expense of the optimization procedure has been reduced by an order of magnitude (with respect to previous control-based wall models) by defining the optimization problem only near the boundaries and carefully constructing the equations governing the optimization problem. Second, no a priori information is required since a near-wall RANS solver is coupled with the LES to provide the controller with information about the mean velocity profile. This approach has been successfully tested in high Reynolds number plane channel flow. Unfortunately, wall models based on purely physical reasoning often lead to an inaccurate LES, particularly on coarse grids and at high Reynolds numbers, because they do not account for the numerical and SGS modeling errors that become large in these types of simulations. To address these errors, optimal control-based wall models have been developed by previous investigators. While these have the demonstrated ability to account for the aforementioned errors, they have two primary drawbacks: 1) high computational expense, due to the optimization procedure, and 2) a lack of predictability, because the control targets are prescribed a priori. REPORT DATE (DD-MMThe goal of this work is to address these two issues in order to make controlbased wall modeling feasible for engineering applications. To reduce the expense, the adjoint equations, which are used to determine the gradients needed for the

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“…The goal is to take more physical phenomena into account, such as heat fluxes [6] or chemical reactions [3] to name some examples. This includes efforts to extend the validity of the wall-model to configurations including streamwise pressure gradients, wallcurvature or separated flows [2,8], in which standard equilibrium formulations can be expected to perform poorly.…”

Section: Introductionmentioning

confidence: 99%

Implementation Methods of Wall Functions in Cell-vertex Numerical Solvers

Jaegle

Cabrit

Mendez

et al. 2010

Flow Turbulence Combust

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Two different implementation techniques of wall functions for cell-vertex based numerical methods are described and evaluated. The underlying wall model is based on the classical theory of the turbulent boundary layer. The present work focuses on the integration of this wall-model in a cell-vertex solver for large eddy simulations and its implications when applied to complex geometries, in particular domains with sudden expansions (more generally in presence of sharp edges). At corner nodes, the conjugation of law of the wall models using slip velocities on walls and of the cell-vertex approach leads to difficulties. Therefore, an alternative F. Jaegle · O. Cabrit · S. Mendez CERFACS, 42 Av. Gaspard Coriolis, 246 Flow Turbulence Combust (2010) 85:245-272implementation of wall functions is introduced, which uses a no-slip condition at the wall. Both implementation methods are compared in a turbulent periodic channel flow, representing a typical validation case. The case of an injector for aero-engines is presented as an example for an industrial-scale application with a complex geometry.

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Approximate Wall Boundary Conditions for Large Eddy Simulations

Cited by 33 publications

References 6 publications

Simulating flow separation from continuous surfaces: routes to overcoming the Reynolds number barrier

Simulating flow separation from continuous surfaces: routes to overcoming the Reynolds number barrier

Wall Models for Large-Eddy Simulation Based on Optimal Control Theory

Implementation Methods of Wall Functions in Cell-vertex Numerical Solvers

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