Hybrid RANS/LES Study of the Development of an Airfoil-Generated Vortex

Abstract

We consider the numerical simulation of a generic lateral vortex, that is generated by a rapidly deflected NACA0021 airfoil. We use the SST k-ω URANS approach and a hybrid RANS-LES method based on the SST model, where a zonal RANS-LES interface is located little downstream of the airfoil trailing edge. The results are assessed by reference with the experimental data. The mean flow behavior and the induced angle of attack of the vortex can be predicted satisfactorily by the URANS approach and the improvement using hybrid RANS/LES is small. The hybrid RANS/LES results exhibit a delayed shear layer instability of the wake, and the arising 2D roller type vortices lead to a significant overprediction of the turbulent shear stress. We then apply a stochastic forcing in the region of the airfoil trailing edge. This leads to a fast generation of turbulent content in the wake and clearly improves the predictions for the turbulent stresses.