Direct measurements of skin friction in complex supersonic flows
1997, American Institute of Aeronautics and Astronautics, Inc. Experimental studies of the direct measurement of skin friction in complex supersonic and hypersonic flows were conducted. A wall-mounted, miniature, cantilever sensor with semiconductor strain gages at the beam base was used to measure the small tangential shear force on a non-intrusive floating element. The use of a double-base silicon rubber compound in the sensing gap reduced maintenance requirements with a small increase in manufacturing and calibration complexity. Measurements were made in a scramjet model at the GASL HYPULSE facility under harsh flow conditions simulating Mach 14 enthalpy with a run time of under half a millisecond. Cold flow tests were performed in the Virginia Tech Supersonic Tunnel at Mach 2.4 to further verify the concept and establish pressure gradient sensitivity in the case of a shock wave impacting directly on the gage head. Measured wall shear values agreed well with theoretical and numerical predictions.