Skin friction measurement

Article By:

Schetz, Joseph A. Department of Aerospace and Ocean Engineering, Virginia Polytechnic Institute and State University, Blacksburg, Virginia.

Last reviewed:2011

DOI:https://doi.org/10.1036/1097-8542.YB110112

Skin friction (or wall shear) is defined as the tangential force per unit area created on a surface that is exposed to a flowing viscous fluid. This quantity is very important to the design, analysis, and understanding of all types of fluid machinery, including, as but a few examples, aircraft, ships, automobiles, piping systems, atmospheric and river flows, and circulatory and pulmonary systems. To put this in perspective, about 50% of the drag, and thus the fuel consumption, of a well-designed passenger aircraft is attributable to skin friction on the wings, fuselage, tails, and engine nacelles. Moreover, the skin friction distribution can play a very important role in identifying and correcting problem areas in fluids devices and systems. Another application for skin friction measurement is as a sensitive input signal for flow control systems. From a basic viewpoint, local skin friction values are central to all data-correlating techniques for turbulent flows, and these correlations form the basis for the development of all turbulence models used in computational fluid dynamics. Accurate measurement is critical, because computational methods still cannot provide sufficiently accurate skin friction results for complex flows. Since this quantity is so important, there is a long history of work in the area starting in the late nineteenth century.

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