Zonal Large-Eddy Simulations and Aeroacoustics of High-Lift Airfoil Configurations

Abstract

High Reynolds number flows are still challenging problems for large-eddy simulations (LES) due to thin small-scale structures e.g. in the near wall regions and often transitional boundary layers which have to be resolved. For this reason, the prediction of high Reynolds number airfoil flow over the entire geometry using LES still requires huge computer resources. To remedy this problem a hybrid zonal RANS-LES method for the flow over an airfoil in high-lift configuration at Re c =106 is presented. In a first step a 2D RANS solution is sought, from which boundary conditions are formulated for an embedded LES domain, which comprises the flap and a sub-part of the main airfoil. The turbulent fluctuations in the boundary layers at the inflow region of the LES domain are generated by controlled forcing terms, which use the turbulent shear stress profiles obtained from the RANS solution. In the second part of the paper a large-eddy simulation of the flow around an airfoil consisting of a slat and a main wing is performed at a Reynolds number of 1.4·106 based on the freestream velocity and the clean chord length to identify the flow phenomena generating slat noise. The freestream Mach number is Ma=0.16 and the angle of attack is 13°. A computational mesh with about 55 million cells is used to resolve the turbulent scales in the boundary layers and within the slat cove region. Results are presented for both the turbulent flow field obtained from the LES and the acoustic field obtained with a computational aeroacoustics method based on acoustic perturbation equations.