INVESTIGATION OF METHODS FOR THE PREDICTION AND ALLEVIATION OF LIFT FAN NOISE

Abstract : A research investigation into the generation, suppression and prediction of fan noise was completed. The theoretical investigations provided insight into the basic noise generating mechanism of fan noise commonly called fan or compressor 'whine'. Acoustic normalizing techniques resulted in a correlation curve of the overall sound power for 13 separate fan and compressor vehicles with each one being from a different design family. Investigation of noise minimization through design techniques incorporated the results of the analytical investigations and the normalized sound power relations. Results indicate the effect or rotor-stator spacing, blade number, RPM, inlet length and centerbody design. Suppression techniques evaluated were wave cancellation, deflection, and absorptive suppressor designs. Test results of an absorptive type suppressor show up to 10.5 db maximum suppression as tested with a sale model fan configuration.