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A study of turbulence at a wall using an electrochemical wall shear-stress meter

Published online by Cambridge University Press:  28 March 2006

James E. Mitchell  and
Thomas J. Hanratty
James E. Mitchell
Affiliation:
Department of Chemistry and Chemical Engineering, University of Illinois, Urbana, Illinois
Thomas J. Hanratty
Affiliation:
Department of Chemistry and Chemical Engineering, University of Illinois, Urbana, Illinois
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Abstract

A technique has been developed to measure the instantaneous shear stress at the boundary over which a liquid is flowing. It is being used to study turbulence in the immediate vicinity of a pipe wall. A reaction is conducted on an electrode mounted flush with a solid wall at high enough voltages to reduce the concentration of the reacting species to zero at the surface. Under these conditions, the rate of reaction is controlled by the rate of mass transfer. The electrode is analogous to a constant-temperature hot-wire anemometer in that the surface concentration is kept constant and the current flowing in the circuit is related to the surface shear stress. For fully developed turbulence the limiting velocity intensity, based on the local average velocity, is 0·32. Some of the velocity fluctuations are as large as the local average velocity and their distribution is nearly symmetric about the average. The ratio of the longitudinal to circumferential scale is about 30 : 1, because the circumferential scale is very small. There is some indication that close to a wall the velocity fluctuations in the circumferential direction are much smaller than the longitudinal fluctuations.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 26 , Issue 1 , September 1966 , pp. 199 - 221
Copyright
© 1966 Cambridge University Press

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