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Measurements of the nearly isotropic turbulence behind a uniform jet grid

Published online by Cambridge University Press:  29 March 2006

Mohamed Gad-El-Hak  and
Stanley Corrsin
Mohamed Gad-El-Hak
Affiliation:
Department of Mechanics and Materials Science, The Johns Hopkins University Present address: Department of Aerospace Engineering, University of Southern California, Los Angeles, California 90007.
Stanley Corrsin
Affiliation:
Department of Mechanics and Materials Science, The Johns Hopkins University
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Abstract

Wind-tunnel turbulence behind a parallel-rod grid with jets evenly distributed along each rod is nearly isotropic. Homogeneity improvement over prior related experiments was attained by the use of controllable nozzles. Compared with the ‘passive’ case, the downwind-jet ‘active’ grid has a smaller static pressure drop across it and gives a smaller turbulence level at a prescribed distance from it, while the upwind-jet grid gives a larger static pressure drop and larger turbulence level. ‘Counterflow injection’ generates larger turbulence energy and larger scales, both events being evidently associated with instability of the jet system. This behaviour is much like that commonly observed behind passive grids of higher solidities.

If the turbulent kinetic energy is approximated as an inverse power law in distance, the (positive) exponent decreases with increasing (downwind or upwind) jet strength, corresponding to slower absolute decay rates. No peculiar decay behaviour occurs when the jet grid is ‘self-propelled’ (zero net average force), or when the static pressure drop across it is zero.

The injection does not change the general behaviour of the energy spectra, although the absolute spectra change inasmuch as the turbulence kinetic energy changes.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 62 , Issue 1 , 8 January 1974 , pp. 115 - 143
Copyright
© 1974 Cambridge University Press

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