Multiphysics Investigation of Hypersonic Boundary Layer Stability by Global Sensitivity Analysis

The influence of nose radius and wall temperature on the first and second modal instabilities has been investigated numerically over a 7-degree half-cone configuration under H3 conditions—the cold hypersonic wind tunnel environment at the von Karman Institute. Linear stability analyses were performed, accompanied by a grid convergence study to ensure discretization-independent results. In agreement with previous studies, the current findings confirm that wall cooling stabilizes the first mode while destabilizing the second mode. In contrast, increasing nose bluntness exerts a stabilizing effect on both modes. These deterministic results contribute to a broader database intended for a global sensitivity analysis. This analysis identifies, at each body location, the parameter that most significantly influences stability behavior, and also evaluates the potential coupled effects between wall temperature and nose bluntness. Specifically, the adopted sensitivity study is a surrogate-based approach. Therefore, a key objective was to develop a surrogate model capable of accurately predicting stability outcomes with minimal computational cost. The investigated parameter ranges—wall temperature from 288 K to 500 K and nose radius from 0.126 mm to 2.500 mm—are consistent with existing experimental data. The sensitivity analysis showed that the nose radius has a bigger influence on the instability amplitudes than the wall temperature, as it damps and delays the modes. Yet, a high coupling between the two parameters is detected around the stagnation region, due to the entropy layer.