Adaptive State Resolved Vibrational Energy Modeling for Hypersonic Flow Simulation

Abstract

Vibrational nonequilibrium is known to significantly influence flowfield and surface properties in a variety of hypersonic flows. Historical low fidelity CFD models for vibrational nonequilibrium, often based on a two-temperature approach, allow for efficient calculations at the cost of potentially large errors in computed output quantities. In contrast, high fidelity state resolved models are generally impractical for engineering analysis due to poor computational efficiency. While globally applied simplifications to full state resolved modeling routines have shown considerable potential for simple zero or one-dimensional flow problems, such simplifications have yet to be demonstrated as practical alternatives to a two-temperature approach for more complex flows of engineering interest. In this work, we explore the possibility of applying spatially adaptive approximations to a state resolved model, such that high fidelity modeling operations are performed only for vibrational levels and for flowfield regions where these operations are deemed necessary. Two different adaptive modeling techniques are proposed, and output quantity sensitivities are assessed for a simple inviscid flow of N 2 over a cylindrical forebody geometry. Excellent accuracy is found in translational and vibrational temperatures for sufficiently conservative choices of model input parameter values, although significant errors are consistently observed for upper vibrational levels within portions of the shock layer.