Theoretical Study of High-Frequency Helicopter Rotor Rotational Noise.
Abstract
The investigation deals with the radiation of rotational noise due to fluctuating forces on the rotar blades of a helicopter, with particular emphasis on studying the effects of chordwise and spanwise differential-pressure profiles. The variation of profiles with azimuth was studies as a possible source of higher harmonic rotational noise. The investigation is more useful at high tip Mach numbers, (>0.6), when rotational noise becomes subjectively more important than broadband noise; high forward speeds, when some peculiar loading profiles and their fluctuations with azimuth are observed and higher frequencies of the acoustic spectra, where the wavelength of the sound radiated is comparable to the blade chord. Previous theories were modified to include the chordwise and spanwise differential pressure profiles. Computer programs were written to compute the r.m.s. value of mth harmonic of sound pressure at any observer position using rotor geometry and operating conditions, field point position relative to the rotor centre, and rotor blade differential-pressures at several chordwise and spanwise stations. A detailed study of the available measured aerodynamic loading data was carried out and it appears that the variation of chordwise blade loading profiles alone accounts for a significiant part of the high-frequency rotational noise from helicopter rotors. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1970
- Accession Number
- AD0721661
Entities
People
- H. K. Tanna
Organizations
- University of Southampton