Sound radiation and caustic formation from a point source in a wall shear layer

infinity, using a previously developed method. Here, omega is the circular frequency of the point source, D is the thickness of the shear layer, and c0 is the ambient sound speed. Stationary and moving sources are analyzed. An infinite sequence of caustic surfaces are created downstream of the source and adjacent to the wall, by the refraction of rays from the source and their subsequent reflection from the wall. The acoustic fields on and off the caustics are obtained. The vorticity of the acoustic field is large on a caustic, but it decays rapidly away from the ''center'' of the caustic surface. That is, the energy of the acoustic field on a caustic is localized. In addition, the caustic surfaces are ''swept back'' by the moving source. The striking similarity between the moving caustic surfaces and the experimentally determined coherent fluid structures, which originate in the laminar sublayer of a turbulent boundary layer and are localized regions of intense vorticity, suggests that the previously proposed mechanism for the formation of these localized coherent fluid structures might be valid. The bursting of these structures and the violent ejection of the fluid away from the sublayer could be one of the mechanisms producing turbulence in the boundary layer. -->

ISSN:	1533-385X 0001-1452
DOI:	10.2514/3.12112
Přístupová URL adresa:	https://explore.openaire.eu/search/publication?articleId=doi_________::82b5fe519643f895e3acce2f6ce4ecd1 https://doi.org/10.2514/3.12112
Přírůstkové číslo:	edsair.doi...........82b5fe519643f895e3acce2f6ce4ecd1
Autor:	Gregory A. Kriegsmann, I. D. Abrahams, Edward L. Reiss
Rok vydání:	1994
Předmět:	Physics Point source Astrophysics::High Energy Astrophysical Phenomena Aerospace Engineering Laminar sublayer Geometrical acoustics Mechanics Acoustic wave Vorticity Physics::Fluid Dynamics Boundary layer Classical mechanics Refraction (sound) Caustic (optics)
Zdroj:	AIAA Journal. 32:1135-1144
ISSN:	1533-385X 0001-1452
DOI:	10.2514/3.12112
Popis:	The propagation of acoustic waves from a high-frequency point source in a shear layer flowing over an infinite rigid plate is considered. Asymptotic expansions of the solution are obtained as k = omegaD/c0 --> infinity, using a previously developed method. Here, omega is the circular frequency of the point source, D is the thickness of the shear layer, and c0 is the ambient sound speed. Stationary and moving sources are analyzed. An infinite sequence of caustic surfaces are created downstream of the source and adjacent to the wall, by the refraction of rays from the source and their subsequent reflection from the wall. The acoustic fields on and off the caustics are obtained. The vorticity of the acoustic field is large on a caustic, but it decays rapidly away from the ''center'' of the caustic surface. That is, the energy of the acoustic field on a caustic is localized. In addition, the caustic surfaces are ''swept back'' by the moving source. The striking similarity between the moving caustic surfaces and the experimentally determined coherent fluid structures, which originate in the laminar sublayer of a turbulent boundary layer and are localized regions of intense vorticity, suggests that the previously proposed mechanism for the formation of these localized coherent fluid structures might be valid. The bursting of these structures and the violent ejection of the fluid away from the sublayer could be one of the mechanisms producing turbulence in the boundary layer.
Databáze:	OpenAIRE
Externí odkaz:	https://explore.openaire.eu/search/publication?articleId=doi_________::82b5fe519643f895e3acce2f6ce4ecd1 https://doi.org/10.2514/3.12112 Zobrazit plný text záznamu