Reports and Memoranda

Reports and Memoranda
Author:
Publisher:
Total Pages: 12
Release: 1980
Genre: Aeronautics
ISBN:

Beginning with no. 650 each hundredth number contains a list of the Reports and memoranda published since the last list.

R & D Abstracts

R & D Abstracts
Author: Technology Reports Centre (Great Britain)
Publisher:
Total Pages: 622
Release: 1981
Genre:
ISBN:

Refraction and Scattering of Sound by a Shear Layer

Refraction and Scattering of Sound by a Shear Layer
Author: Robert H. Schlinker
Publisher:
Total Pages: 196
Release: 1980
Genre: Acoustic surface waves
ISBN:

The angle and amplitude changes for acoustic waves refracted by a circular open jet shear layer were determined. The generalized refraction theory was assessed experimentally for on axis and off axis acoustic source locations as source frequency varied from 1 kHz to 10 kHz and free stream Mach number varied from 0.1 to 0.4. Angle and amplitude changes across the shear layer show good agreement with theory. Experiments confirm that the refraction theory is independent of shear layer thickness, acoustic source frequency, and source type. A generalized theory is, thus, available for correcting far field noise data acquired in open jet test facilities. The effect of discrete tone scattering by the open jet turbulent shear layer was also studied. Scattering effects were investigated over the same Mach number range as frequency varied from 5 kHz to 15 kHz. Attenuation of discrete tone amplitude and tone broadening were measured as a function of acoustic source position and radiation angle. Scattering was found to be stronger at angles close to the open jet axis than at 90 deg, and becomes stronger as the acoustic source position shifts downstream. A scattering analysis provided an estimate of the onset of discrete tone scattering.