Short duration flows in shock tunnels excite vibrations in models.
A diaphragm mounted flush with the surface of the model is connected to piezoceramic cantilever beams which provide outputs proportional to the bending in them induced by flow across the diaphragm. Skin friction transducers have been developed for use in the Calspan shock tunnels but only brief design and performance details have been reported. There is an absolute dearth of data from experiments in short duration, high enthalpy hypersonic facilities. However, skin friction is particularly difficult to measure with reasonable accuracy. For these reasons one of the key tests of a CFD code is its ability to predict skin friction coefficients correctly, especially in turbulent boundary layers.
It is related to fundamental phenomena such as boundary layer transition and heat transfer and its integral over a model is a significant component of the vital performance parameter, drag. Skin friction is an important parameter in hypersonic flow.
Simmons, in Experimental Heat Transfer, Fluid Mechanics and Thermodynamics 1993, 1993 Skin Friction
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