A model for rotor broadband noise prediction

Abstract

This thesis describes a frequency domain formulation for predicting the broadband self-noise due to an open rotor or propeller.  The integration in the formulation can be evaluated on the real blade surface rather than on the projected disk or blade mean-chord surface, as has been done previously, thereby avoiding the commonly made assumption of flat plate geometry.  It is assumed that the noise is predominantly due to trailing edge interaction of the hydrodynamic pressure associated with the turbulent boundary layer over the rotor blades (self-noise).  The unsteady blade loading, which constitutes the aerodynamic sound source, is predicted using modifications to Amiet’s thin aerofoil theory, and a prediction of the boundary layer surface pressure frequency - wavenumber spectrum.  This is obtained by combining the wavenumber spectrum due to Corcos, the measured frequency spectrum due to Chou and George, and the boundary layer thickness measurements of Brooks.

A generalised frequency domain formulation has been developed for making rotor broadband noise predictions.  It can be used for making broadband and tonal noise predictions, and is valid in both the near field and the far field.  A simplified expression for making far-field self-noise prediction is presented.  This far-field frequency-domain formulation is computationally far more efficient than the general formulation.  It is shown to reduce to the classic Gutin solution of propeller tonal noise prediction when the steady surface pressure source is confined to the propeller-projected disc.

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