Free-stream density perturbations in a reflected-shock tunnel
Focused laser differential interferometry is used to quantify the free-stream density perturbations in the T5 reflected-shock tunnel. The investigation of reflected-shock tunnel disturbances is motivated by the study of hypervelocity boundary-layer instability and transition. Past work on hypersonic wind-tunnel noise is briefly reviewed. New results are reported for hypervelocity air flows at reservoir enthalpies between 5 and 18 MJ/kg at Mach ≈ 5.5. Statistical analysis finds no correlation of RMS density perturbations with tunnel run parameters (reservoir pressure, reservoir mass-specific enthalpy, free-stream unit Reynolds number, free-stream Mach number, and shot number). Spectrograms show that the free-stream disturbance level is constant throughout the test time. Power spectral density estimates of each of the experiments are found to collapse upon each other when the streamwise disturbance convection velocity is used to eliminate the time scale. Furthermore, the disturbance level depends strongly on wavelength. If the disturbance wavelength range of interest is between 700 μm and 10 mm, the tunnel noise is measured to be less than 0.5 % with the focused laser differential interferometer.
© 2014 Springer-Verlag Berlin Heidelberg. Received: 28 August 2013; Revised: 18 December 2013; Accepted: 4 January 2014; Published online: 16 January 2014. This work is based in part on the Ph.D. dissertation of the first author (Parziale 2013); additionally, it was an activity that was part of National Center for Hypersonic Laminar–Turbulent Research, sponsored by the ''Integrated Theoretical, Computational, and Experimental Studies for Transition Estimation and Control'' project supported by the US Air Force Office of Scientific Research and the National Aeronautics and Space Administration (FA9552-09-1-0341). The authors would like to thank Bahram Valiferdowsi and Joe Jewell for help running T5, Ross Wagnild for help with the program to compute the run conditions, and Ivett Leyva for her helpful comments and thoughts.