Technique for direct measurement of skin friction in high enthalpy impulsive scramjet flowfields

Abstract

A new technique was developed that allowed the direct measurement of skin friction on the walls of the inlet and combustion chamber associated with two scramjet models being tested in two hypersonic impulse facilities. The scramjet experiments took place in both the NASA Ames 16-in. high-enthalpy hypersonic and the CALSPAN 96-in. shock tunnels. Flight Mach number conditions of 12-16 were tested. Miniature, plastic, cantilever skin friction sensors were developed for the present tests. The use of plastic provided the necessary high-frequency response, high-shear sensitivity, and low-thermal sensitivity. The cantilever design was incorporated to minimize the gauge sensitivity to normal pressure. The gauge performance was found to be excellent for a variety of controlled evaluation experiments, where the results agreed very well with other independent direct measurements and accepted empirical correlations. The gauge also proved to be accurate and reliable in the two impulsive scramjet experiments.