High-Enthalpy Effects on Hypersonic Boundary-Layer Transition: Experimental and Numerical Comparison

In this paper, results from two experiments performed at California Institute of Technology’s T5 free-piston reflected shock tunnel are compared to numerical stability computations conducted using various stability analysis tools. The goal of this comparison is to begin understanding the range of boundary-layer transition predictability using different stability approaches for high-enthalpy flows. The analysis is focused on the physics of the second-mode instability at high enthalpy and the role of high-temperature effects. Although the stability solvers considering thermochemical nonequilibrium were best at estimating the measured second-mode frequency (f_2M ≈ 1250 kHz for shot 2990, f_2M ≈ 1235 kHz for shot 3019), they overpredicted the most amplified frequency by approximately 16–23%. A moderate spread in the predicted most amplified frequency was also observed between the different solvers. The solvers estimated a most amplified frequency range of approximately 1450–1550 kHz for shot 2990 and approximately 1525–1650 kHz for shot 3019. There was also significant inconsistency observed in predicting the peak N-factor magnitude, ranging from N = 12.5–16 for shot 2990 and from N = 12.3–19 for shot 3019.