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An experimental investigation of the detention of airborne smoke in the wake bubble behind a disk

Published online by Cambridge University Press:  29 March 2006

W. Humphries  and
J. H. Vincent
W. Humphries
Affiliation:
Department of Applied Physics, University of Strathclyde, Glasgow
J. H. Vincent
Affiliation:
Department of Applied Physics, University of Strathclyde, Glasgow
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Abstract

Experiments have been performed in a low-speed wind tunnel to determine the detention time of airborne smoke particles that become trapped in the wake vortex (or bubble) region behind flat disks placed perpendicular to the flow. Using a laser transmissometer to detect the smoke, its detention time was obtained from the time-dependent decay of the smoke in the disk bubble during the time immediately following the removal of the source of smoke. The dimensionless group H, the product of the detention time and the mainstream air velocity divided by the disk diameter, is seen to be a constant equal to 7.44 ± 0.52 for Reynolds numbers in the range 2000–40000. This result is compatible with a simple fluid-mechanical model which describes the transport of fluid-borne scalar entities across the bubble boundary by turbulent diffusion. The investigation suggests that H should be unique for the flow about a disk over a wide range of conditions, and further suggests the possibility that similar unique values for H can exist for flow about other obstacles. The number H has potential applications in a number of physical and engineering research areas.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 73 , Issue 3 , 10 February 1976 , pp. 453 - 464
Copyright
© 1976 Cambridge University Press

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