Detached-Eddy Simulation of Aerodynamic Flows Using a Reynolds-Stress Background Model and Algebraic RANS/LES Sensors

Kurzfassung

A new variant of delayed detached-eddy simulation (DDES) based on the Low-Re epsilon-h-RSM as RANS background model is presented which is optionally combined with novel algebraic sensors for the RANS/LES switch. The RSM is aimed to improve RANS-mode predictions of pressure-induced separations on smooth surfaces, while the new sensors eval- uate boundary-layer properties to distinguish between attached and detached flow regions and place the RANS/LES interface at separation onset. After calibration and basic validation for decaying isotropic turbulence, the epsilon-h-based DDES is applied to a backward-facing step flow with massive separation and compared to experiments. The results are well in line with original DDES and can be further improved by applying stochastic forcing of the turbulent subgrid stresses. For the HGR-01 airfoil at stall, both the RSM-based approach and the algebraic sensors are found essential in capturing separation onset at the trailing edge and ensuring LES mode in the separated flow. However, the actual DES computations still suffer from under-resolved turbulence in the separated LES region when compared to PIV measurements, which can neither be compensated by stochastic forcing, nor by a different RANS model or a local grid refinement. Thus, the need to extend the present method by a more sophisticated forcing becomes evident.