ANALYTICAL STUDIES OF SOME ACOUSTIC PROBLEMS OF JET ENGINES
The propagation and generation of acoustic waves in a choked nozzle is considered where pressure and entropy fluctuations caused by gas stream non-uniformities like 'hot spots,' are incident on the nozzle entrance. A novel noise-generation mechanism is found which produces acoustic waves of strength proportional to the entrance entropy fluctuation and local gradient of the mean flow velocity. A transformation is introduced which relates the solutions of problems involving the propagation of acoustic waves in a moving medium to the solutions of associated problems in a stationary medium. The method is described by discussing the Sommerfeld problem for a half plane in a subsonic flow. For supersonic case, all the diffraction problems are related to a single reference problem. A decomposition of the pressure field in a 'geometrical optics' field and a diffracted field is given, showing some remarkable similarities to the subsonic solution. The radiation of acoustic modes from a duct immersed in a subsonically moving medium is treated by a similar transformation. The presence of the uniform flow has roughly the same effect as, an increase in frequency of the incident wave, at constant mode number. The effect of acoustical lining on the radiation pattern is examined, and side radiation is shown to be greatly reduced for the lower order modes.
Jet Propulsion LaboratoryCalifornia Institute of Technology, 4800 Oak Grove Drive
Pasadena, CA USA 91103
Office of the Secretary of TransportationOffice of Noise Abatement, 1200 New Jersey Avenue, SE
Washington, DC USA 20590
- Candel, S M
- Publication Date: 1976-5
- Pagination: 240 p.
- TRT Terms: Acoustics; Aircraft noise; Compressors; Diffraction; Ducts; Electromagnetic radiation; Entropy (Communications); Jet engines; Jet propelled aircraft; Mathematical analysis; Mathematical models; Noise; Nozzles; Plane waves; Pressure; Sound transmission; Subsonic flow; Supersonic aircraft; Supersonic flow; Supersonic speed
- Old TRIS Terms: Jet engine noise; Jet engine nozzles; Supersonic flight
- Subject Areas: Aviation; Environment; Vehicles and Equipment;
- Accession Number: 00154836
- Record Type: Publication
- Source Agency: National Technical Information Service
- Report/Paper Numbers: DOT-TST-76-104 Intrm Rpt.
- Contract Numbers: DOT-OS-20197
- Files: TRIS, USDOT
- Created Date: Jun 22 1978 12:00AM