Large-Eddy and Detached-Eddy Simulation of the Flow Around High-Lift Configurations

Abstract

The paper is concerned with separated turbulent flows past a flat plate and an unswept wing (NACA-4415 airfoil) at high angles of attack. For both configurations large-eddy simulations (LES) were carried out. Additionally, the flow past an infinitely thin plate was simulated by detached-eddy simulation (DES). First a relatively low chord Reynolds number Re c = 20, 000 was chosen for the airfoil case yielding a leading-edge stall for both angles of attack (α = 12° and 18°) investigated. The flow field in this range of Re c and α is dominated by asymmetric vortex shedding predefined by strong vortices developing almost periodically in the vicinity of the trailing edge. The life cycle of these vortical structures is controlling the entire flow field. At the leeward side of the airfoil, a large clockwise rotating recirculation region of nearly constant pressure exists. For α = 18° the features of the flow around the flat plate were found to be very similar to the airfoil case, because both flows separate at comparable positions and are dominantly controlled by the shedding motion of the trailing-edge vortex. The DES predictions of the flat plate lead to reasonable agreement with the LES results concerning the mean flow field. However, comparing DES and LES predictions carried out on the same grid yielded remarkable deviations especially in the representation of the free shear layer and the higher-order statistics. Hence the standard DES formulation needs some adjustments. Finally, some first LES results for the airfoil flow at a higher Reynolds number Re = 100, 000 are presented showing a completely different flow behavior than the low-Re case. This includes a laminar separation bubble, transition behind the bubble, and separation of the turbulent boundary layer at about 70% chord length.