Quantitative schlieren measurements of coherent structures in a cavity shear layer |
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Authors: | S Garg L N Cattafesta III |
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Institution: | (1) High Technology Corporation, 28 Research Drive Hampton, VA 23666, USA, US |
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Abstract: | Quantitative flow-field data were obtained in a planar shear layer spanning an open cavity with an extension of the schlieren
method. The technique is based on the measurement of light-intensity fluctuations in a real-time schlieren image. Data were
collected using a fiber-optic sensor embedded in the imaging screen coupled to a photodetector. Time-resolved measurements
of the instantaneous density gradient at a point in the two dimensional flow cross section were thus obtained. Detailed surveys
were carried out with both the optical instrument as well as a hot wire at a Mach number of 0.25 and with the optical instrument
alone at a Mach number of 0.6. A comparison of the results shows that the non-intrusive technique can accurately measure the
growth rates of instability waves in the initial “linear” region of the shear layer. The density-gradient fluctuations measured
at different locations (and times) were synchronized by using a microphone inside the cavity as a reference and integrated
to yield profiles of the density fluctuations associated with the dominant large-scale structures in the shear layer. Such
quantitative visualization is expected to clarify the mechanism of sound generation by shear-layer impingement at the cavity
trailing edge and elucidate the nature of this sound source.
Received: 28 December 1999/Accepted: 15 March 2000 |
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