Simulation of Sound Generation by Vortices Passing the Trailing Edge of Airfoils

Abstract

The interaction of vorticity with the trailing edge of airfoils is an important source of airframe noise. In order to study this process, in the present paper the interaction of a single vortex with the trailing edge of a symmetric Joukowsky airfoil under 0° angle of attack is calculated by the solution of nonlinear disturbance equations with a RANS mean flow in the Mach number range from 0.2 to 0.5. Nonlinearities are taken into account up to first order. The emphasis of the present study rests on the assessment of the influence of the Mach number and non-linearities on the generated sound field. It has been found that the sound intensity downstream of the profile scales approximately like M**4, which is near to the theoretical value. Taking into account non-linearities increases the sound pressure level in case of mathematically negative rotating initial vortices and decreases it in case of positive rotating ones. This should be kept in mind in the assessment of solutions obtained by the linearized Euler equations.