Hybrid RANS-LES Simulations of Incipient Airfoil Trailing Edge Separation

Abstract

Hybrid RANS-LES, such as, Detached Eddy Simulation (DES) based models offer significant advantages over LES or RANS for massively separated flows. However, in cases of mild separation, their performance is not well understood, and for this reason this paper presents a comparative study of URANS, DES, DDES and IDDES simulations on a NACA0015 wing section at 11° incidence, and an airfoil chord based Reynolds number of 1 million. This poses a severe challenge for numerical simulations as the skin friction remains very close to zero after the separation point in the separated zone. The prediction of such flow was found to be very sensitive to the different modelling strategies. This test case with mild trailing edge separation from a smooth surface illustrates significant differences in the numerical simulations among the four approaches. The results showed that the IDDES formulation produced the more reliable results when compared to the experimental data in relation to surface pressure, velocity profiles and Reynolds stresses in the wake. The URANS, DES, and DDES methodologies varied significantly in results with URANS and DDES indicating fully attached flow, while DES predicting a much delayed separation point.