Accession Number : ADA133958

Title :   Experimental and Analytical Studies of Shielding Concepts for Point Sources and Jet Noise.

Descriptive Note : Interim rept.,


Personal Author(s) : Wong,Raymond Lee Man

PDF Url : ADA133958

Report Date : May 1983

Pagination or Media Count : 189

Abstract : This analytical and experimental study explores concepts for jet noise shielding. Model experiments centre on solid planar shields, simulating engine-over-wing installations and 'sugar scoop' shields. Tradeoff on effective shielding length is set by interference 'edge noise' as the shield trailing edge approaches the spreading jet. Edge noise is minized by (1) hyperbolic cutouts which trim off the portions of most intense interference between the jet flow and the barrier and (2) hybrid shields - a thermal refractive extension (a flame); for (2) the tradeoff is combustion noise. In general, shielding attenuation increases steadily with frequency following low frequency enhancement by edge noise. Although broadband attenuation is typically only several decibels, the reduction of the subjectively weighted perceived noise levels is higher. In addition, calculated ground contours of peak PN dB (perceived noise level) show a substantial contraction due to shielding: this reaches 66% for one of the 'sugar scoop' shields for the 90 PN dB contour.

Descriptors :   *Jet engine noise, *Shielding, Acoustics, Noise reduction, Planar structures, Scoops, Barriers, Aircraft noise

Subject Categories : Acoustics

Distribution Statement : APPROVED FOR PUBLIC RELEASE