On the application of wavelets to LES sub-grid modelling

The wavelet-based multi-resolution analysis technique is used to develop a novel approach to the modelling of the sub-grid terms in the large-eddy simulation equations. This new approach is called WaveLES. A numerical framework for the solution of the projected equations is developed for one and three-dimensional problems. The WaveLES method is assessed in a priori tests on an atmospheric turbulent time series, and a direct numerical simulation. A posteriori tests are carried out for the Burgers equation

Development of a multiscale LES model in the context of a modal discontinuous Galerkin method

International audienceThis paper introduces a variational multiscale simulation (VMS) approach in the context of high-order discontinuous Galerkin (DG) discretizations. First, a new calibration of the Smagorinsky model parameter (CSΔ)(CSΔ) is proposed in terms of the DG discretization (grid size, hh, and polynomial order, pp) and the selected VMS scale partition. Second, an efficient and simple implementation of the VMS version of the Smagorinsky model is presented. The dissipation properties of the DG discretizations for different values of hh and pp are then analysed based on Taylor–Green vortex computations in the limit of inviscid flow. The low levels of dissipation found for high-order DG discretizations emphasize the suitability of this type of discretization for LES. The performance of the presented approach is demonstrated by comparing DG/VMS computations of the Taylor–Green vortex at Re=3000Re=3000 with a reference spectral DNS

On the use of biorthogonal interpolating wavelets for large-eddy simulation of turbulence

Recent work in the field of turbulence modelling has demonstrated the benefits of the wavelet-based multiresolution analysis technique as a tool for the formulation of the large-eddy simulation (LES) equations. In this formalism, the LES equations are obtained by projecting the Navier-Stokes equations onto a hierarchy of wavelet spaces. This paper investigates the use of biorthogonal interpolating wavelets as a basis for this projection, placing special emphasis on the wavelet-based differential operators that define this mapping. A detailed analysis of their convergence properties is presented and compared to those of their orthogonal counterpart, the Daubechies wavelets. Based on this study, we highlight the weaknesses of the unlifted interpolating wavelet representation for LES sub-grid modelling. Finally, we establish a link between the unlifted framework and the sampling-based LES approach recently proposed in the literature. © 2012 Elsevier Inc

Periodic Hill

In this chapter, we focus on the use of high-order discontinuous Galerkin (DG) methods to perform simulations of the turbulent flow over periodically arranged hills, which corresponds to configuration TC-F1 in the TILDA project (Periodic Hill)

DNS and LES of the Flow Over Periodic Hills Based on a Discontinuous Galerkin Approach

International audienceA high-order discontinuous Galerkin (DG) approach is used for the DNS and LES of the flow over periodically arranged hills. In order to assess the capacity of the DG method to capture the Reynolds-number dependent features of the flow, four Reynolds numbers are considered: 2800, 10 595, 19 000, and 37 000. The DG solutions are compared with the reference data available in the literature. For Reb = 10595 the no-model and the WALE LES approaches are compared. The hp-convergence analyses performed for the DNS demonstrate the superior performance of increasing the polynomial order as compared to refining the mesh. It appears from this study that the use of a subgrid modelling approach together with an appropriate level of local hp-refinement could greatly improve the solution without penalising the computational cost of the simulation

Study of a Cooling Device of Confined Impacting Air Jets on a Heating Cylinder

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elsA-Hybrid: an all-in-one structured/unstructured solver for the simulation of internal and external flows. Application to turbomachinery

This paper reports recent work on the extension of the multiblock structured solver elsA to deal with hybrid grids. The new hybrid-grid solver is called elsA-H (elsA-Hybrid), is based on the investigation of a new unstructured-grid module has been built within the original elsA CFD (computational fluid dynamics) system. The implementation benefits from the flexibility of the object-oriented design. The aim of elsA-H is to take advantage of the full potential of structured solvers and unstructured mesh generation by allowing any type of grid to be used within the same simulation process. The main challenge lies in the numerical treatment of the hybrid-grid interfaces where blocks of different type meet. In particular, one must pay attention to the transfer of information across these boundaries, so that the accuracy of the numerical scheme is preserved and flux conservation is guaranteed. In this paper, the numerical approach allowing to achieve this is presented. A comparison between the hybrid and the structured-grid methods is also carried out by considering a fully hexahedral multiblock mesh for which a few blocks have been transformed into unstructured. The performance of elsA-H for the simulation of internal flows will be demonstrated on a number of turbomachinery configurations

Internal Aerodynamic Test Cases

This section gathers the descriptions of all test cases concerning internal flows, as well as the most important results obtained by the participants in the IDIHOM project. The test cases comprise a transonic compressor (NASA Rotor 37), a subsonic nozzle (JEAN), low pressure turbine cascades in turbulent (T106A) and transitional conditions (T106C) and finally 2 validation cases, namely a bump flow from the DESIDER project, and the periodic flow over a 2D hill from the ERCOFTAC QNET CFD database. Depending on the test case, RANS, LES and even DNS computations were performed