Low-frequency rotational noise in closed-test-section wind tunnelsThe effects of closed-section wind-tunnel walls on the sound field radiated from a helicopter rotor are investigated by means of numerical simulations, summarizing the findings reported by Mosher (1986). The techniques used to model the rotor and the test section (including geometry, wall absorption, and measurement location) are outlined, and the results are presented in extensive tables and graphs. It is found that first-harmonic acoustic measurements obtained in a hard-walled wind tunnel twice as wide as the rotor diameter do not accurately represent the free-field rotational noise, that the relationship between the sound-pressure levels in the wind tunnel and in the free field is complex, that multiple near-field measurements are needed to characterize the direct acoustic field of the rotor, and that absorptive linings are of little value in enlarging the accurate-measurement zone.
Document ID
19880030078
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Mosher, Marianne (NASA Ames Research Center Moffett Field, CA, 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