Accession Number : AD0431329

Title :   MECHANISMS OF AERODYNAMIC SOUND PRODUCTION,

Corporate Author : ADVISORY GROUP FOR AERONAUTICAL RESEARCH AND DEVELOPMENT PARIS (FRANCE)

Personal Author(s) : Powell, A.

Report Date : APR 1963

Pagination or Media Count : 20

Abstract : Sound production and flow instability are two inseparable characteristics of any compressible fluid flow. It is common to look upon an incompressible flow field as being by vorticity, a viewpoint often used on studies of flow instability. This classical viewpoint can be generalized to the compressible flow field when it becomes apparent that the vorticity may be considered to induce the complete flow field which includes the radiated sound field as an intergral part. The theory is developed and demonstrated by application to a free flow, the sound power being shown to depend on the eighth power of the flow velocity, as is well established by experiment. In the case of aeolian tones, the vortex shedding is directly associated with the sound field. This is also true of the edgetone phenomenon where the vortex shedding also reacts on the jet flow itself causing a selective feedback which, together with the instability characteristic, gives rise to the distinctive frequency characteristics. Measurements confirm that the effective sound source is of the dipole type with the acoustic power depending on the jet velocity raised to the sixth power. If a highly resonant system is added to the edge-tone system the action may be governed by the resonant feedback; then both theory and experiment show that the sound power is dependent on about the fourth power of the jet velocity. (Author)

Descriptors :   (*AERODYNAMIC CHARACTERISTICS, SOUND), (*SOUND, AERODYNAMIC CHARACTERISTICS), (*VORTICES), MOTION, SPINNING(MOTION), FLUID FLOW, RESONANCE, CAVITATION NOISE, FREQUENCY, INTENSITY, STABILITY.

Distribution Statement : APPROVED FOR PUBLIC RELEASE