Influence of Shaft Angle of Attack on Sound Radiation by Subsonic Propellers

The formulation to account for effects of propeller angle of attack on acoustic radiation by propellers is presented. A propeller operating at an angle of attack presents a nonuniform ine ow situation that is known to have a pronounced ine uence on noise. Noise predictions, based on this new formulation, are compared with measured wind-tunnel data. Predictions for observers e xed in the propeller plane are also included to assess the ine uence of shaft angle of attack. Nomenclature c0 = ambient speed of sound f = function dee ning blade surface l = local force per unit area of blade acting on e uid lr = component of loading vector in direction of radiation vector, liri M = source Mach number Mr = component of source Mach vector in direction of