Measurement of Skin Friction in the University of Texas at Arlington Arcjet

Abstract

Arcjet flows are known to have significant uncertainties associated with the fundamental flow quantities. A detailed characterization is critical to augment the current understanding of these complex flows as well as developing, screening, and qualifying thermal protection systems. Classically, estimations of skin friction have been made indirectly using heat flux analogies. These techniques, however, are marred by high levels of measurement uncertainty and require a priori assumptions about the flowfield. Directly measuring the wall shear stress removes the demand for these assumptions. A direct measurement of shear stress in supersonic high-enthalpy flow at the Office of Naval Research/University of Texas at Arlington arcjet facility has been conducted. The measured wall shear stress was (average combined calibration uncertainty), which matches well with estimations for laminar flow. Two shear stress sensors separated by a distance of 1.905 cm (0.75 in.) were integrated into a 20 deg half-angle shear-wedge platform. The two sensors tracked together within 10% of each other, implying a uniform flowfield over the region studied. Approximately 1.5 s into the test window, a steady increase in skin friction was observed. The cause of this nonphysically accurate increase in the shear stress measurement is discussed.