Verification and Validation Issues in Hypersonic Stability and Transition Prediction
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Copyright 2014 by Helen Reed, Eduardo Perez, Joseph Kuehl, Travis Kocian and Nicholas Oliviero. The development, validation, and introduction of physics-based approaches for stability and transition prediction will lead to smaller and more manageable uncertainties in the design of hypersonic vehicles. Through mechanism identification, verification, and validation activities for two-and three-dimensional geometries, the following have been learned in applying stability formulations: 1) Related to verification of the basic state, the acid test is to refine the basic state until the stability results do not change; 2) A good verification test for the stability formulationis to be sure the linear problem is correctly modeled; 3) In validation, it is very important to work on the same geometries computationally and experimentally and confirm them; for example, model alignment and freestream flow angularity are found tobe important; 4) From verification studies on three-dimensional geometries, numerical errors, especially near the windward plane, can seed the stationary crossflow instability in the supposedly undisturbed basic state; the stationary crossflow instability is sensitive; 5) The marching path is important for three-dimensional geometries and should be in the group-velocity direction; the N factor has some uncertainty in it, and caution should be used in quoting it with precision; and 6) Nonlinear effects should be included in detailed studies of crossflow instability necessitating a nonlinear parabolized stability equation or direct numerical simulation approach.
