PREDICTION OF AIRFOIL NOISE IN COMPRESSIBLE TURBULENT FLOWS

The sound production of an isolated airfoil due to harmonic vortical gusts in the incoming flow is treated. A new prediction model is presented which is based on an acoustic analogy. It makes use of the boundary-element method and the dual reciprocity method to solve the aerodynamic and acoustic equations. The model is valid for inviscid, compressible mean flows as long as no shocks are present. Since the true airfoil geometry is considered, the model is well suited to study the influence of airfoil camber and thickness distribution on the noise production. A first parametric study indicates that the airfoil thickness has an influence on the sound generation, i.e. thick airfoils radiate less noise than thin ones. This is in agreement with experimental and numerical results which were obtained for low Machnumber flows. The effect of airfoil camber is found to be less pronounced. The new prediction models may give important insights for the noise reduction on a number of technical devices such as turbo fans from aircraft engines or helicopter rotors.