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The effect of flow oscillations on cavity drag

Published online by Cambridge University Press:  21 April 2006

M. Gharib  and
A. Roshko
M. Gharib
Affiliation:
Graduate Aeronautical Laboratories, California Institute of Technology, Pasadena, CA 91125, USA Present address: Department of Applied Mechanics and Engineering Sciences, University of California, San Diego, La Jolla, California 92093, USA.
A. Roshko
Affiliation:
Graduate Aeronautical Laboratories, California Institute of Technology, Pasadena, CA 91125, USA
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Abstract

An experimental investigation of flow over an axisymmetric cavity shows that self-sustained, periodic oscillations of the cavity shear layer are associated with low cavity drag. In this low-drag mode the flow regulates itself to fix the mean-shear-layer stagnation point at the downstream corner. Above a critical value of the cavity width-to-depth ratio there is an abrupt and large increase of drag due to the onset of the ‘wake mode’ of instability. It is also shown by measurement of the momentum balance how the drag of the cavity is related to the state of the shear layer, as defined by the mean momentum transport $\rho\overline{u}\overline{v}$ and the Reynolds stress $\rho\overline{u^{\prime}v^{\prime}}$, and how these are related to the amplifying oscillations in the shear layer. The cavity shear layer is found to be different, in several respects, from a free shear layer.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 177 , April 1987 , pp. 501 - 530
Copyright
© 1987 Cambridge University Press

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