Velocity and Temperature Measurements in a High Mach Number Shock-Turbulence Interaction

Abstract

Shock wave turbulence interactions are important problems with ubiquitous applications in high-speed flight and propulsion. The complex physical processes during the interaction are not fully understood, where contemporary high-fidelity numerical simulations have brought into question classical linear interaction analyses (LIA). The differences are most pronounced at high Mach number (>2). The objective of this study was to experimentally examine the role of a normal shock wave on the modification of velocity and temperature fluctuations to provide an empirical basis to help close the emerging knowledge gap between classical and contemporary theories. The experiments were performed in a pulsed wind tunnel facility at Mach 4.4. The freestream disturbances provided the test-bed for the study, where the Taylor Reynolds numbers (Reλ) were varied over a range of 80 to 170. The pulsed operation enabled sufficiently large statistical samples. A Mach stem normal shock was generated through the interaction of two mirrored oblique shock waves. Molecular tagging velocimetry and two-line planar laser induced fluorescence thermometry were conducted upstream and downstream of the normal shock wave and the fluctuating intensities were compared. The measured axial velocity fluctuation amplification factor (⟨UDS^ 2 ⟩ / ⟨ UF S^′2 ⟩) was nominally 1.1-1.2 over the Reynolds number range tested. The measured values were consistent with LIA. The temperature fluctuation amplification factor [(⟨TDS ′2 ⟩ / ⟨TDS⟩^2 ) / (⟨TF S^′2 ⟩ / ⟨TF S⟩^2 )]^1/2 was found to vary between 3.0-4.5, where the lowest Reynolds number condition saw the highest freestream disturbances and largest amplification. The freestream fluctuations were primarily in the entropic mode, which is believed to lead to the significantly higher amplification of the entropic mode reported in these measurements.