A new subgrid scale model is proposed for Large Eddy Simulations in complex geometries. This model which is based on the square of the velocity gradient tensor accounts for the effects of both the strain and the rotation rate of the smallest resolved turbulent fluctuations. Moreover it recovers the proper y
3 near-wall scaling for the eddy viscosity without requiring dynamic procedure. It is also shown from a periodic turbulent pipe flow computation that the model can handle transition.

/pdf/subgrid-scale-stress-modelling-based-on-the-square-of-the-e05h19jine.pdf

Subgrid-scale stress modelling based on the square of the velocity gradient tensor

A subgrid scale model for large eddy simulations of turbulent premixed combustion is developed and validated. The approach is based on the concept of artificially thickened flames, keeping constant the laminar flame speed sl0. This thickening is simply achieved by decreasing the pre-exponential factor of the chemical Arrhenius law whereas the molecular diffusion is enhanced. When the flame is thickened, the combustion–turbulence interaction is affected and must be modeled. This point is investigated here using direct numerical simulations of flame–vortex interactions and an efficiency function E is introduced to incorporate thickening effects in the subgrid scale model. The input parameters in E are related to the subgrid scale turbulence (velocity and length scales). An efficient approach, based on similarity assumptions, is developed to extract these quantities from the resolved velocity field. A specific operator is developed to exclude the dilatational part of the velocity field from the estimation of...

A thickened flame model for large eddy simulations of turbulent premixed combustion

An eddy-viscosity based, subgrid-scale model for large eddy simulations is derived from the analysis of the singular values of the resolved velocity gradient tensor. The proposed σ-model has, by construction, the property to automatically vanish as soon as the resolved field is either two-dimensional or two-component, including the pure shear and solid rotation cases. In addition, the model generates no subgrid-scale viscosity when the resolved scales are in pure axisymmetric or isotropic contraction/expansion. At last, it is shown analytically that it has the appropriate cubic behavior in the vicinity of solid boundaries without requiring any ad-hoc treatment. Results for two classical test cases (decaying isotropic turbulence and periodic channel flow) obtained from three different solvers with a variety of numerics (finite elements, finite differences, or spectral methods) are presented to illustrate the potential of this model. The results obtained with the proposed model are systematically equivalent or slightly better than the results from the Dynamic Smagorinsky model. Still, the σ-model has a low computational cost, is easy to implement, and does not require any homogeneous direction in space or time. It is thus anticipated that it has a high potential for the computation of non-homogeneous, wall-bounded flows.

/pdf/using-singular-values-to-build-a-subgrid-scale-model-for-4pzhmm2pkk.pdf

Using singular values to build a subgrid-scale model for large eddy simulations

https://www.coria-cfd.fr/images/8/8f/Pub_2004_Lartigue_CF.pdf

Compressible large eddy simulation of turbulent combustion in complex geometry on unstructured meshes

https://hal.archives-ouvertes.fr/hal-00803230/document

Large Eddy Simulations of gaseous flames in gas turbine combustion chambers

Development of High-Order Taylor-Galerkin Schemes for LES

The unstructured flow solver AVBP of CERFACS is presented. The basic concepts of the program are described, and various computational results are presented for a large spectrum of applications ranging from steady-state external aerodynamics to unsteady turbulent flows with and without combustion. The code solves the compressible Navier-Stokes equations on hybrid grids of arbitrary cell type. The code is built on a modular software library and has been ported to a wide range of parallel computers.

Michael Rudgyard

Papers

Development of High-Order Taylor-Galerkin Schemes for LES

Steady and Unsteady Flow Simulations Using the Hybrid Flow Solver AVBP

Upwind iteration methods for the cell vertex scheme in one dimension

A cell-vertex approach to local mesh refinement for the 3-D Euler equations

Stabilised finite element methods for steady incompressible flow