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Direct measurements of skin friction in a turbulent boundary layer with a strong adverse pressure gradient

Published online by Cambridge University Press:  19 April 2006

D. Frei  and
H. Thomann
D. Frei
Affiliation:
Institute of Aerodynamics, Swiss Federal Institute of Technology, Zurich
H. Thomann
Affiliation:
Institute of Aerodynamics, Swiss Federal Institute of Technology, Zurich
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Abstract

This paper describes a new balance, suitable for direct measurement of skin friction in turbulent boundary layers with severe pressure gradients. The gaps between the floating element and the surrounding wall are filled with a liquid in order to eliminate disturbing pressure forces on the element. The resulting friction forces are measured with piezo-electric transducers with high sensitivity and extremely small element displacement.

Skin friction measurements were taken in the turbulent boundary layer of a wind tunnel with circular cross-section at M [les ] 0·25. Severe adverse pressure gradients were generated by means of a step on the wall or, alternatively, by a conical centre body.

The new apparatus was mainly used to investigate the error of Preston tubes in adverse pressure gradients. It was necessary to develop a new measuring technique to improve the repeatability of the Preston tube readings.

The Preston tube error was found to depend on both the local pressure gradient P = (dp/dx) ν/ρ3τ and on the Preston tube diameter uτd/ν and to be independent of the upstream pressure distribution for the range of parameters covered by the experiments.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 101 , Issue 1 , 13 November 1980 , pp. 79 - 95
Copyright
© 1980 Cambridge University Press

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