Hilde Ouvrard

Accuracy Improvement for Finite-Volume Vertex-Centered Schemes Solving Aeroacoustics Problems on Unstructured Meshes

The paper considers two ways of accuracy enhancement at simulating the transport of acoustic disturbances on unstructured meshes with the help of vertex-centered algorithms. The first approach is based on the implementation of quasi-1D high-order differences to calculate the fluxes through the cell faces in the unstructured case. The second way is the usage of quadratic polynomial reconstruction of variables within the finite-volume method. A posteriori estimation of accuracy of the both methods is performed on example of the model problem.

The Role of Different Errors in Classical LES and in Variational Multiscale LES on Unstructured Grids

The effects of numerical viscosity, subgrid scale viscosity and grid resolution are investigated in LES and VMS-LES simulations of the flow around a circular cylinder at Re = 3, 900 on unstructured grids.

Variational Multiscale LES and Hybrid RANS/LES Parallel Simulation of Complex Unsteady Flows

We study a new hybrid RANS/Variational Multiscale LES (VMS-LES) model for bluff body flows. The simulations have been carried out using a parallelized solver, based on a mixed element/volume formulation on unstructured grids. First, the behavior of a VMS-LES model with different subgrid scale models is investigated for the flow past a circular cylinder at Reynolds number Re =3900. Second, a new strategy for blending RANS and LES methods in a hybrid model is described and applied to the simulation of the flow around a circular cylinder at Re = 140000.

Quality of classical and variational multiscale LES simulations of the flow around a circular cylinder

The role of subgrid scale (SGS) viscosity is investigated in LES and VMS-LES simulations of the flow around a circular cylinder at Re=20000 on unstructured grids. The separation between the largest and the smallest resolved scales in the VMS formulation is obtained through a variational projection operator and finite-volume cell agglomeration. Two different non-dynamic eddy-viscosity SGS models are used both in classical LES and in VMS-LES. The sensitivity of the results to different parameters, such as the value of the SGS model input coefficient or the agglomeration level and to numerical viscosity in VMS-LES, is also addressed. Finally, a possible indicator of quality of the LES and VMS-LES predictions is examined.

Mixed subgrid scale models for classical and variational multiscale large-eddy simulations on unstructured grids

The scale similarity (SS) idea was first introduced by Bardina et al. (1980). Following this idea the subgrid-scale stress tensor can be modeled through the modified Leonard tensor, which can be computed as a function of the variables resolved in LES by means of the application of an additional explicit filter. In the original idea, this filter should be the same as the grid one. It has been shown in a priori tests in the literature (see (Meneveau and Katz, 2000) for a review) that the SS model correlates very well with the exact SGS stress tensor and represents quite well energy backscatter from the unresolved to the resolved scales. However, when the scale-similarity SGS model is used alone in actual large-eddy simulations, it does not provide enough SGS dissipation and the simulations may undergo numerical instability. Therefore, the modified Leonard tensor (or SS term) is always used in combination with an eddy-viscosity term, leading to the so-called mixed models (Meneveau and Katz, 2000).