RANS / CAA based prediction of NACA0012 broadband trailing edge noise and experimental validation

Abstract

The prediction quality of a fast Computational Aeroacoustics (CAA) approach is studied for noise generated at a NACA 0012 trailing edge. Broadband spectra, the power law underlying their Mach number scaling, and the effect of Reynolds Number on the spectra are juxtaposed against published data from measurements and results from a semi-empirical prediction tool. The CAA method rests on the use of Reynolds Averaged Navier-Stokes (RANS) solutions to describe the turbulent flow problem around the airfoil. Acoustic Perturbation Equations (APE) are solved in the time domain, using a vortex source term, which is a function of turbulent field quantities. The acoustic approach was sccessfully validated in other works by utilizing turbulence data from Large Eddy Simulation (LES) to prescribe the unsteady sound sources. For the fast CAA approach applied in this work unsteady vortex sound sources are determined by a stochastic method, which generates 4D spatio-temporal synthetic turbulence that very accurately accompishes a local realization of all statistical and mean-flow features provided by steady RANS. Based on these prerequisites it becomes now feasible to make an assessment as to which acoustic accuracy can be achieved with such a hybrid RANS / CAA prediction method, bearing in mind the approximative nature and limited turbulence resolution of RANS: