Direct Skin Friction Measurements at Mach 10 in a Hypervelocity Wind Tunnel

Abstract

This investigation concerns the design, build, and testing of direct-measuring skin friction sensors capable of performing in sustained hypersonic flow and detecting transition. A multistep approach tested the sensors through bench-test and wind-tunnel facilities. The sensors underwent National Institute of Standards and Technology traceable calibrations with well-documented uncertainties. The calibration process characterized static, thermal, pressure, and dynamic responses. Validation testing was conducted in a supersonic tunnel at Mach 4.0. The main investigations were conducted in Arnold Engineering Development Complex Tunnel 9. The skin friction sensor was integrated into a steel 155.6-cm-long (61.27 in.-long), 7 deg half-angle cone model. Flow was nominally maintained at Mach 10 and a stagnation temperature of 1250 K (2250°R). The stagnation pressure and unit Reynolds number were varied over 2.3–43.4 MPa (330–6300 psia) and (), respectively. Skin friction was measured over boundary-layer states including early transitional, transitional, and turbulent flows. Wall shear ranged between 0.92 and 340 Pa (0.02 and 7.1 psf), whereas the skin friction coefficients ranged 0.0003–0.0060. The uncertainty of the skin friction sensor remained at of the measurement for a 95% confidence level. The experimental measurements demonstrated favorable agreement with independent analyses including numerical predictions and Reynolds analogy methods.