SPECTRAL CONDITIONING OF PROPELLER NOISE FROM BROADBAND SOURCES

The effect of turbulent loading on the noise radiated by an advanced aircraft propeller is assessed using a spectral conditioning technique which allows the inclusion of the non-linear effects associated with source rotation. The method allows the steady-source noise at a microphone to be estimated by removing the effect of measured on-blade unsteady loading. The operation of the method is demonstrated by using numerically simulated data, demonstrating the effectiveness of the technique in extracting the steady-source sound. Experimental results are presented showing the effect of random loading on the acoustic field of a propeller in an axial flow and at incidence. It is shown that, for the range of conditions and microphone positions considered, the effect of turbulent loading on the radiated noise can vary from about 2–8 dB, being stronger upstream than downstream.