EFFECT OF WAKE STRUCTURE ON BLADE-VORTEX INTERACTION PHENOMENA - ACOUSTIC PREDICTION AND VALIDATION

The higher harmonic control aeroacoustic rotor test conducted at Duits -Nederlandse Wind Tunnel has made extensive measurements of the rotor aerodynamics, far-field acoustics, wake geometry, and the blade motion for powered descent flight conditions. These measurements have been u sed to validate and improve the prediction of blade-vortex interaction (BVI) noise. The improvements made to the BVI modeling after the eval uation of the test data are discussed. The effect of these improvement s on the acoustic-pressure predictions is shown. These improvements in clude restructuring the wake, modifying the core size, incorporating t he measured blade motion into the calculations, and attempting to impr ove the dynamic blade response. A comparison of four different impleme ntations of the Ffowcs Williams and Hawkings equation is presented. A common set of aerodynamic input has been used for this comparison.