Development of Direct-Measuring Skin-Friction Gauges for Hypersonic Flight Tests

Abstract

Anewtypeofdirect-measuring skin-frictiongaugewasdevelopedforthehigh-speed,high-temperatureenvironmentofturbulentboundary-layere owsinsupersoniccombustionramjet (scramjet)engines, with tests progressing from ground tests to an actual hypersonic scramjet-integrated e ight vehicle. The skin friction gauge was specie cally developed for installation on the Hyper-X e ight vehicle (X-43A). The design was nonnulling, with a sensing head that was e ush with the model wall and surrounded by a small gap. Unlike previous skin-friction sensor designs, this gauge eliminated water cooling and gap-e lling oil, in addition to a radically different e exure design. The design was verie ed by repeatable tests in a well-documented Mach 2.4 cold e ow, with results within 10 ‐15% of Cf estimates from simple theory. The sensor was qualie ed for e ight through a rigorous series of environmental tests, including pressure, temperature, vibration, shock, acceleration, and heat e ux tests. Finally, the skin-friction gauge was tested in the Hyper-X engine model (HXEM), a full-scale ‐partial-width wind-tunnel model of the e ight vehicle engine, at Mach 6.5 enthalpy in a freejet facility at NASA Langley Research Center. Successful testing in the HXEM provided the e nal verie cation of the gauge before installation in the X-43A e ight vehicle engine.