Peak heat flux prediction of hypersonic flow over compression ramp under vibrationally excited free-stream condition

Abstract

In hypersonic shock tunnel experiments, the high-temperature reservoir gas expands and accelerates so rapidly that there is not enough time for vibrational energy relaxation. As a result, thermal nonequilibrium gas flow is frequently encountered in the test section, and this significantly affects the measured heat flux. In this paper, hypersonic compression-ramp flows are studied numerically to investigate the effect of incomplete vibrational energy accommodation on the separation flow structure and peak heat flux in the reattachment region under low-to-medium Reynolds number and high Mach number conditions. Numerical results and theoretical analysis suggest that the vibrational energy accommodation has no noticeable impact on the length scale of the separation zone, but strongly influences the peak heat flux of the separated ramp flows. Decomposing the peak heat flux into translational--rotational energy and vibrational energy components, $q_{\rm{tr}}$ and $q_{\rm{v}}$, respectively, we find that $q_{\rm{v}}/q_{\rm{tr}}$ characterizes the nonequilibrium degree of the vibrational energy accommodation. A formula for predicting the peak heat flux is then proposed, taking the effect of incomplete vibrational energy accommodation into consideration. Finally, surface heat flux measurements in a hypersonic shock tunnel indicate that a deviation of up to 13\% in total peak heat flux could arise if vibrational energy accommodation is not considered under the vibrationally excited free-stream condition.

Influence of thermochemical nonequilibrium on expansion tube air test conditions: A numerical study

“…9, a numerical study on a u 1 % 4 km/s air condition in the LENS-X ET (acceleration tube length ¼ 26.5 m) showed the existence of vibrational nonequilibrium, which is known to influence experimental results. 10,11 Likewise, for similar air test conditions (u 1 % 3-4 km/s) in this same facility, the numerical and experimental results reported in Ref. 12 gave indications that vibrational nonequilibrium may exist.…”

Can vibrational pumping occur via O2–N2 collisions in nonequilibrium vibrationally excited air?

“…At speeds of around 1-2 km/s (temperature around 1000-2000 K), vibrational nonequilibrium is important [7][8][9][10][11]. Under these conditions during de-excitation, the intermode vibration-vibration-translation (VVT) reaction O2(i1) + N2(i2) ↔ O2(f1) + N2(f2), where i1 and i2 are the initial vibrational quantum numbers of molecules 1 and 2, respectively, and f1 and f2 are the final vibrational quantum numbers of the respective molecules, may cause a particular phenomenon known as 'vibrational pumping' where the vibrational energy of the two molecules, initially in equilibrium, diverges with one increasing and the other decreasing.…”