Measurement of hypersonic high-enthalpy boundary layer transition on a 7º cone model

Abstract

Surface pressure fluctuations on a 7o half-angle cone were measured in a high-enthalpy hypersonic flow. Eight piezoelectric pressure transducers were mounted on the cone’s surface to obtain the frequency characteristics of the surface pressure. An additional four piezo-resistive pressure transducers were used to monitor surface pressure histories. To determine the transition point in the boundary layer, 62 miniature thermocouples were also mounted on the surface. The test was performed in the free-piston shock tunnel HIEST at the JAXA-Kakuda Space Center. In order to produce sufficient Reynolds number for the transition flow, shots with high stagnation pressure were conducted (stagnation pressure up to 55 MPa). Stagnation enthalpy was varied from 8 MJ/kg to 18 MJ/kg. Consequently, the free-stream unit Reynolds number was approximately 1 to 3 million. Frequency spectra of surface pressure fluctuations were obtained by fast Fourier transform, with a frequency resolution of 39 kHz. To reduce several irrelevant noisy components in the spectra, four of eight piezo-electric transducers were not exposed to the flow, for use as a baseline to cancel out the noisy components. Although this noise cancellation was unsuccessful, frequency spectra of surface pressure fluctuations were obtained at high enthalpy and high Reynolds number. Frequency peaks, which were expected to be the 2 mode instability, were observed up to H0 = 12 MJ/kg and P0 = 50 MPa, at which the free-stream unit Reynolds number was approximately 1.6 million.