A New Capability for Predicting Helicopter Rotor Noise in Hover and in Flight
ARMY AIR MOBILITY RESEARCH AND DEVELOPMENT LAB HAMPTON VA LANGLEY DIRECTORATE
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This paper discusses a new theory and a computer program for realistic calculation of acoustic pressure signature and spectrum of rotor and propeller noise. Many of the common restrictions of already existing theories are removed by using the new theory which is consistent with all previous theories. Only deterministic pressure fluctuations may be used in the program at this stage of development. This will limit the applicability of the program to relatively high tip speeds where it is known that high frequency unsteady pressure fluctuations do not contribute significantly to the sound level. There are very few blade surface pressure measurements and reliable acoustic data available to test the theory in full. Comparison with the measured acoustic data of a high-speed propeller by Hubbard and Lassiter, using limited aerodynamic data in the blade tip region for acoustic calculations, has shown good agreement so far. One important contribution of the new theory is believed to be the removal of the compactness assumption which can introduce errors in acoustic computations. The new capability will be used to study this effect.