Frequency-domain method for rotor self-noise prediction

A frequency-domain formulation is described for predicting the broadband self-noise radiation from an open rotor; or propeller, situated in a smooth, mean flow. It is assumed that the noise is predominantly due to the interaction between the hydrodynamic pressure associated with the turbulent boundary layer over the rotor blades, and their trailing edges. Integration of the aerodynamic sources is performed over the actual blade surface rather than on the projected disk or nonthickness blade surface, as having being done in previous studies, thereby avoiding the commonly made assumption of flat plate geometry. The validation is performed of predictions of the measured broadband noise from an R212 propeller. Acceptable agreement between the measurement and predicted noise spectrum is obtained. The broadband self-noise directivity is also investigated, which is found to vary only slowly with azimuthal angle, with a main lobe in the direction of the propeller axis. The theory is used to undertake a parameter study of the broadband noise radiation from the propeller. Effects due to chord, blade number, and angle of attack are also discussed.