Mach 10 Bow Shock and Gas-Cap Unsteadiness Measurements Using Rayleigh Scattering

摘要

This study demonstrates the usefulness of instantaneous and mean density rho, standard deviation sigma, relative standard deviation sigma/rho, and product standard deviation sigma * rho acquired using a low-sampling-rate instantaneous (10 ns) laser-based method to study effects of high-frequency phenomena on offbody freestream, bow-shock wave, and gas-cap unsteadiness. Spatial correlations of relative flow unsteadiness are acquired using laser Rayleigh scattering performed along a 38.7 mm line containing 200 pixels spanning the freestream, gas cap, near-normal, and oblique shocks created by a multipurpose crew vehicle model in the NASA Langley 31-in. Mach 10 air wind tunnel. A total of 371 instantaneous images are acquired at a fixed stagnation temperature of 990 +/- 11 K and five stagnation pressures spanning 2.41-10.0 MPa (350-1454 psi). Maximum s occurs at the bow-shock-wave spatial density profile first-derivative maximum for a near-normal and oblique shock. Maximum sigma/rho and sigma * rho occur at the bow-shock-wave spatial density profile second-derivative maximum and minimum, respectively, for both the near-normal and oblique shocks. At P-0 = 1454 psi, maximum s (normal shock) >5/2 sigma (gas cap), and sigma (gas cap) is >2 sigma (freestream). Additional spatially averaged unsteadiness correlations with flowfield conditions are presented.