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The Magnification of Roughness Drag by Pressure Gradients

Published online by Cambridge University Press:  04 July 2016

J. F. Nash  and
P. Bradshaw
J. F. Nash
Affiliation:
Aerodynamics Division, NPL
P. Bradshaw
Affiliation:
Aerodynamics Division, NPL
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Summary

A simplified analysis indicates that the increase in profile drag of an aerofoil due to an isolated roughness element is, in general, different from the drag of the element measured on a flat plate with the same free-stream velocity. This “magnification” effect is caused chiefly by the effect of the pressure gradients on the boundary layer downstream of the roughness element.

The degree of magnification is not closely approximated by the ratio of local to free-stream dynamic pressure and, in many typical cases, the contribution to the drag due to roughness elements may be seriously under-estimated in this way.

Measurements of the effect of the initial boundary-layer thickness on the subsequent development of a turbulent boundary-layer in an adverse pressure gradient support the theoretical conclusions.

Type
Research Article
Information
The Aeronautical Journal , Volume 71 , Issue 673 , January 1967 , pp. 44 - 46
Copyright
Copyright © Royal Aeronautical Society 1967

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References

1.Spence, D. A.The development of turbulent boundary layers. J Ae Sci, p 3, January 1956.CrossRefGoogle Scholar
2Thompson, B. G. J., A critical review of existing methods of calculating the turbulent boundary layer. ARC 26 109-FM 3492. Aug. 1964.Google Scholar
3.Squire, H. B. and Young, A. D. The calculation of the profile drag of aerofoils. ARC R & M 1838. Nov. 1937.Google Scholar