AN ANALYTICAL AND EXPERIMENTAL STUDY OF SOUND PROPAGATION AND ATTENUATION IN VARIABLE-AREA DUCTS
The performance of sound suppression techniques in ducts that produce refraction effects due to axial velocity gradients was evaluated. A computer code based on the method of multiple scales was used to calculate the influence of axial variations due to slow changes in the cross-sectional area as well as transverse gradients due to the wall boundary layers. An attempt was made to verify the analytical model through direct comparison of experimental and computational results and the analytical determination of the influence of axial gradients on optimum liner properties. However, the analytical studies were unable to examine the influence of non-parallel ducts on the optimum linear conditions. For liner properties not close to optimum, the analytical predictions and the experimental measurements were compared. The circumferential variations of pressure amplitudes and phases at several axial positions were examined in straight and variable-area ducts, hard-wall and lined sections with and without a mean flow. Reasonable agreement between the theoretical and experimental results was obtained.
Virginia Polytechnic Institute and State University, BlacksburgDepartment of Agronomy
Blacksburg, VA USA 24061
- Nayfeh, A H
- Kaiser, J E
- Marshall, R L
- Hurst, L J
- Publication Date: 1978-10
- Pagination: 134 p.
- TRT Terms: Acoustic ducts; Acoustics; Aircraft; Computer programs; Confined flow; Ducts; Engines; Instruments for measuring loads or pressure; Linings; Measurement; Noise control; Performance; Pressure; Sound transmission
- Uncontrolled Terms: Aircraft engines; Noise reduction
- Old TRIS Terms: Axial flow; Ducted flow; Engine inlets; Pressure measurement; Wall flow
- Subject Areas: Aviation; Vehicles and Equipment;
- Accession Number: 00198898
- Record Type: Publication
- Source Agency: National Technical Information Service
- Report/Paper Numbers: NASA-CR-135392 Final Rpt.
- Contract Numbers: NAS3-18553
- Files: TRIS
- Created Date: Oct 17 1980 12:00AM