Vol. 2, No. 8, 2007

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ISSN: 1559-3959
Density measurements in a supersonic jet

Catalina Elizabeth Stern, José Manuel Alvarado and Cesar Aguilar

Vol. 2 (2007), No. 8, 1437–1448
Abstract

We use a nonintrusive optical technique for heterodyne detection of the light scattered elastically by the molecules of a moving transparent gas, a phenomenon known as Rayleigh scattering. It can be shown that the signal that comes out of the photodetector is proportional to the spatial Fourier transform as a function of time of the density fluctuations, for a wave vector given by the optical set-up. This is the only technique we are aware of that can study density fluctuations inside a flow.

In this paper we present results obtained from a supersonic axisymmetric air jet. The signal that comes out of the photodetector is processed, and the power spectrum calculated. In the spectrum, density fluctuations of two different origins can be identified: acoustic, that is, those that propagate at the speed of sound and are related to pressure variations, and entropic, those that have constant pressure and are convected by the flow. At certain locations we have found an additional peak related to the interaction between the flow and the shock structure. Furthermore, Rayleigh scattering can be used to visualize the shock structure of the flow. We provide supporting images for our results.

Keywords
aeroacoustics, Rayleigh scattering, supersonic flow
Milestones
Received: 23 April 2007
Accepted: 8 May 2007
Published: 1 October 2007
Authors
Catalina Elizabeth Stern
Laboratorio de Acústica
Facultad de Ciencias
Ciudad Universitaria
Universidad Nacional Autónoma de México
Avenida Universidad 3000
Col. Copilco el Bajo, Del. Coyoacán
Distrito Federal 04510
Mexico
José Manuel Alvarado
Laboratorio de Acústica
Facultad de Ciencias
Ciudad Universitaria
Universidad Nacional Autónoma de México
Avenida Universidad 3000
Col. Copilco el Bajo, Del. Coyoacán
Distrito Federal 04510
Mexico
Cesar Aguilar
Laboratorio de Acústica
Facultad de Ciencias
Ciudad Universitaria
Universidad Nacional Autónoma de México
Avenida Universidad 3000
Col. Copilco el Bajo, Del. Coyoacán
Distrito Federal 04510
Mexico