The uses and abuses of the acoustic analogy in helicopter rotor noise predictionThe generation of noise by helicopter rotor blades is considered theoretically, reviewing recent analyses based on the acoustic analogy (where the effect of fluid motion is replaced by fictitious sources in an undisturbed fluid). The fundamental principles of the acoustic approach are explained and illustrated with diagrams; the governing Ffowcs-Williams/Hawkings equations are written with a reformulated quadrupole term; and the directivity of noise produced (1) by regions with steep gradients (such as shock surfaces) and (2) by boundary-layer quadrupoles (tip-vortex and blade wakes) is shown to be the same as that of thickness noise. The need to include both (1) and (2) in acoustic-analogy computations is indicated.
Document ID
19880030073
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Farassat, F. (NASA Langley Research Center Hampton, VA, United States)
Brentner, Kenneth S. (NASA Langley Research Center Hampton, VA, United States)
Date Acquired
August 13, 2013
Publication Date
January 1, 1987
Subject Category
Acoustics
Meeting Information
Meeting: National Specialists'' Meeting on Aerodynamics and Aeroacoustics