Geometrical and numerical considerations in computing advanced-propeller noise

A previously developed technique for numerically solving the acoustic analogy equation for rotating surfaces with supersonic regions results in smooth pressure-time waveforms. The method appears to provide results superior to those of other schemes because it eliminates erratic "noise" in the computed waveforms and deals only with nonsingular integrals. This article discusses the application of the method to propeller-type rotor blades. Several different sweep geometries are considered, and presented results show the effect of blade shape on the noise produced and on the numerical procedure for computing that noise. Computed waveforms exhibit expected behavior, deduced from analysis of the retarded blade shapes (acoustic planforms) and the critical points along the blade edges where the Mach number in the direction of the observer equals one.