Towards Efficient Hybrid RANS-LES for Industrial Aeronautical Applications

Kurzfassung

Three complementary approaches for reducing the grid-resolution requirements in hybrid RANS-LES computations, namely (a) the use of wall functions, (b) the application of locally embedded WMLES instead of global WMLES, as well as (c) local grid adaptation in LES regions, are assessed for different test cases up to an industry-relevant aeronautical flow. In this context, targeted improvements and an extension to general 3D geometries of an embedded WMLES method in a second-order accurate, unstructured compressible finite-volume solver are presented. For the wall functions and the embedded WMLES, which are applied to the NASA hump flow and the CRM-HL aircraft configuration, significant computational efficiency gains relative to corresponding reference simulations are demonstrated, while the loss of predictive accuracy compared to experiments can be limited to acceptable levels. Using a refinement indicator based on the locally resolved turbulent kinetic energy, the grid adaptation applied to the NASA hump flow and the NACA0021 at stall conditions yields partly even improved results compared to computations on globally-refined fixed grids, but the computational overhead due to the iterative refinement and averaging process was not yet included in this study. With grid-point savings ranging between 1/3 and more than 2/3 of grid points compared to respective reference meshes, all considered methods offer potential towards more efficient hybrid RANS-LES simulations of complex flows, although their accumulated potential through combination still needs to be explored.