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An experimental study of the mechanism of intermittent separation of a turbulent boundary layer

Published online by Cambridge University Press:  20 April 2006

Qing-Ding Wei  and
Hiroshi Sato
Qing-Ding Wei
Affiliation:
Department of Mechanics, Beijing University, Beijing, China
Hiroshi Sato
Affiliation:
Institute of Interdisciplinary Research, University of Tokyo, Komaba, Meguro-ku, Tokyo, Japan
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Abstract

A wind-tunnel investigation was made of the mechanism of separation of a two-dimensional turbulent boundary layer on a convex wall. The flow field was observed visually by using a large number of smoke wires arranged in various ways. Statistical quantities were obtained by newly developed direction-sensitive hot-wire probes and flow-direction meters. Smoke pictures show localized backflow spots in the separation region. They occur intermittently, grow downstream, merge with each other and eventually cover the whole flow field. Measurements of instantaneous flow direction show that velocity fluctuations in the separation region are strongly three-dimensional. The backflow factor, which is defined as the fraction of time of occurrence of backflow, is used for the quantitative description of the separation region. The role of large-scale ordered motions in the turbulent separation was investigated by use of the conditional sample and average technique. It was confirmed that a localized backflow is initiated by a large-scale low-speed lump of fluid which travels downstream.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 143 , June 1984 , pp. 153 - 172
Copyright
© 1984 Cambridge University Press

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