Wall temperature and high enthalpy effects on hypersonic boundary layer stability and transition
Date
2025
Authors
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Publisher
University of Delaware
Abstract
The hypersonic boundary layer transition study is crucial for controlled and sustainable flight. Although crucial, the mechanisms underlying the transition are still poorly understood, even in a low-noise environment. Understanding of these extreme environment flow phenomena can lead to significant advances in aerospace flight technologies. Different modes of disturbances present in the hypersonic boundary layer undergo modal growth eventually leading to turbulence. ☐ The objective of this dissertation is to understand the dynamics of modes and their interactions due to wall temperature and high-enthalpy effects on hypersonic boundary layer transition. This research study utilizes computational fluid dynamics (CFD) as well as stability analysis tools such as linear stability theory (LST), linear parabolized stability equations (PSE), and non-linear parabolized stability equations (NPSE). This research combines theoretical understanding of first and second-mode instability with practical application to predict and mitigate turbulent transition in hypersonic boundary layers. The mean flow Lagrangian invariants are introduced to relate it with obliqueness of the first-mode instability. The effects of stream-wise thermal gradients on the growth of second-mode instability are investigated. The computational results for the pattern wall temperature study are compared with experiments conducted in the AFOSR–Notre Dame Large Mach-6 Quiet Tunnel at the University of Notre Dame and show good consistency. The wall thermal configurations proposed in this study significantly delay the laminar-to-turbulent transition that arises due to second-mode instabilities. In addition to that, this research presents unique wall thermal patterns that do not affect the growth of second-mode instabilities. The computational results for high-enthalpy studies are compared with other numerical codes. The sensitivity of high-enthalpy hypersonic boundary layer flows to non-linearity is investigated. A 1D-CNN machine learning model was proposed to predict the critical N-factor. This data-driven model presented in this dissertation is the one that can be used as a preliminary assessment to predict the transition rapidly with minimal computational effort.
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Keywords
Wall temperature, High enthalpy, Hypersonic boundary layer, Linear stability theory, Computational fluid dynamics