2013-04-30

Unstructured high order discretization schemes: an enabling technology for reliable LES in an industrial context

Dr. Koen Hillewaert, Cenaero - Simulation technologies for Aeronautics, Gosselies (Belgium)

25 Jun 2013, 17:00–18:30; Location: S4|10-1

The simulation of turbulent flows by the Large Eddy Simulation (LES) or Direct Numerical Simulation (DNS) approaches requires extremely low numerical dispersion and dissipation. Finite Element-like high-order methods such as the discontinuous Galerkin (DGM), spectral difference (SDM) and spectral element methods (SEM), ... have attracted considerable interest lately since they seem to bridge the gap between the accuracy of dedicated academic flow solvers and the geometric flexibility of industrial solvers. Currently DGM features amongst the most mature methods in this class. Next to very interesting dispersion and dissipation properties, it furthermore provides computational efficiency and a simple way of checking grid resolution without requiring additional computations. These advantages make DGM a powerful tool for high fidelity simulation of transitional and turbulent flows.

The development of a CFD code based on DGM for industrial LES is discussed, from the assessment for DNS to the preliminary development of adequate subgrid scale (SGS) models for LES. Thereby the code is assessed with respect to academic codes on canonical benchmarks, and applied subsequently to more complex configurations, illustrating the potential of DGM for DNS and LES in industry.

The first part of the talk concerns the assessment for DNS. First of all, a detailed comparison with finite difference methods is performed on the simulation of the transition of the Taylor-Green vortex at Re=1600. A second academic application concerns the 2D periodic hill at Re=2800. These results are put into perspective with respect to the results presented by other authors at the first and second International Workshop on Higher Order Methods for CFD. The method is applied to the DNS of the flow around a low pressure turbine blade.

The second part of the talk discusses the development and assessment of industrially practical LES modeling strategies. Validation is performed on canonical benchmarks such as homogeneous turbulence at very high Reynolds number and channel flow. The focus lies on simple and local models, applicable in complex geometries. Therefore typically dynamic parameter tuning procedures can not be considered, as these require one or more homogeneous directions. Currently the implicit LES (ILES) approach is assessed. This approach supposes that the numerical dissipation of the method is sufficiently targeted to provide an adequate SGS model. The main advantage of this approach is that it does not require tuning or regime-specific calibration. The ILES approach is tested on a transitional airfoil and compared to DNS, showing excellent agreement for a much smaller computational cost.

Category: CE Seminar

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