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Turbulence and Shear Flow Phenomena -1 First International Symposium

ISBN 打印: 1-56700-135-1

CORRELATION BETWEEN COHERENT STRUCTURES AND WALL SHEAR STRESS FLUCTUATIONS (SIMULTANEOUS MEASUREMENT OF VELOCITIES, WALL SHEAR STRESS AND FLOW VISUALIZATION)

Abstract

When studying organized motions in a turbulent wall flow, it is useful to clarify the relationship between organized motions and wall shear stress fluctuations. This is because the momentum transfer from the wall region to the outer region and vice versa causes wall shear stress fluctuations in a turbulent boundary layer. In past studies, the relationship between organized motions and wall shear stress fluctuations was investigated using a single hot wire (or array of hot wires) and a wall shear stress gage. However, the relationship between wall shear stress fluctuations and visualized flow pattern was not reported. In the present study, velocity and wall shear stress fluctuations were measured simultaneously and flow pattern was observed. In order to identify organized motions on the basis of wall shear stress fluctuations, a scheme for detecting the organized motions was used. This scheme detects the organized motions when the ratio of the amplitude of wall shear stress fluctuations to the standard deviation of the wall shear stress fluctuations (i.e. r.m.s. value) is greater or less than a threshold level. Experiments showed that ejection events detected using wall shear stress fluctuations with a threshold correspond to ejections identified using the side and top views of dye flow visualization. In addition sweep events detected using wall shear stress fluctuations with a threshold correspond to sweeps recognized using the end view of dye flow visualization.
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