Simulation of acoustic scattering from a trailing edge

Abstract

Unsteady two-dimensional flow calculations were performed about a thin NACA airfoil with a bluff-body vortex generator positioned at 98% chord. The bluff body produced unsteady vortex shedding, which simulated large coherent eddies in a boundary layer. The shed vortices interacted and occasionally paired as they convected past the sharp trailing edge of the airfoil. The CFD calculations clearly showed acoustic waves emanating from the airfoil trailing edge. The Ffowcs Williams and Hawkings equation [J. E. Ffowcs Williams and D. L. Hawkings, Philos. Trans. R. Soc. A 264, 321–342 (1969)] was used to compute the acoustic field generated by the unsteady aerodynamic field. Directivity maps and Mach-number scalings have been obtained and compared with the theoretical predictions for trailing-edge noise. The noise below the airfoil displays characteristics typical of a sound field scattered from a sharp edge. The noise above the airfoil is more complicated; it contains significant contributions from both the scattered acoustic field and the bluff-body vortex generator. The effects of spanwise correlation length and the choice of integration surface will also be discussed.