Experimental study of high-speed impulsive rotor noise in a wind tunnel

Results are presented from high-speed impulsive noise (HSIN) tests of two model rotors, conducted in an acoustically-lined wind tunnel. While one of the rotors has rectangular planform blades, the other uses 30-deg sweptback tips of 'F30' configuration. The F30 tips are found to yield substantial noise reduction in the direction of maximum HSIN generation, in virtue of the delay of delocalization toward higher tip speeds; this, in turn, is a consequence of the suppression of transonic effects obtained by the sweptback tips. It is stressed that blade tip geometry may strongly influence noise radiation through the modification of shock surface geometries.