Hypersonic Stability and Transition Prediction

Abstract

The development, validation, and introduction of physics-based approaches for accurate stability and transition prediction will lead to much smaller and manageable uncertainties in the design of hypersonic vehicles. Through mechanism identification, verification, and validation activities for 2D and 3D geometries, the following lessons have been learned: Related to the verification of the basic-state solution, the acid test is to refine the basic state until the stability results do not change. In validation activities in hypersonic flow, it is very important to work on the same geometries computationally and experimentally, and confirm it; for example, model alignment and freestream flow angularity are found to be important. As observed from verification studies on 3D geometries, numerical errors in the steady basic state, especially near the attachment line, can seed the stationary crossflow instability in the supposedly undisturbed basic state; the stationary crossflow instability is sensitive. The marching path is important for 3D geometries and should be in the group velocity direction; N-factor has some uncertainty in it for 3D geometries and caution should be used in quoting it with precision. Nonlinear effects must be included in detailed studies of crossflow instability necessitating a nonlinear parabolized stability equation approach or direct numerical simulation.