Numerical Simulation of Receptivity to Freestream Acoustic Disturbances for Hypersonic Boundary Layer over a Blunt Body with Chemical and Thermal Nonequilibrium

Currently most numerical methods for computing hypersonic flows with thermochemical non-equilibrium are based on the shock-capturing approach. Shock capturing schemes reduce to first-order accuracy near the shock and have been shown to produce spurious oscillations behind curved strong shocks. There is a need to develop new met hods capable of simulating non-equilibrium hypersonic flow fields with uniformly high-order accuracy and avoid spurious oscillations near the shock. Uniformly high order schemes are useful in simulation of flows aimed at studying receptivity and laminar-turbulent transition due to requirement of capturing varying scales of lengths and time. Though much progress has been made in theoretical and experimental aspects of study of transition, non-equilibrium effects have been recently included, mainly in the shock capturing schemes. Most of the efforts at direct numerical simulation of receptivity and transition are for perfect gas flow or "cold" hypersonic flows. For practical problems in hypersonic flows, high-temperature effects of thermal and chemical nonequilibrium are important and cannot be modeled by a perfect gas model. Therefore, it is necessary to include the real gas models in the numerical simulation of hypersonic boundary layer transition in order to accurately predict flow field parameters. In this study a new high order method capable of simulating hypersonic flows with thermochemical nonequilibrium has been developed. The method is developed based on the state-of-the-art real gas models for thermo-chemical nonequilibrium and transport phenomena. The new method has been tested and validated for a number of test cases over a wide span of free stream conditions.;Real gas effects have been recently included in theoretical and numerical studies of receptivity and laminar-turbulent transition for hypersonic flows. Prediction of transition is important to estimate thermal and mechanical loads on a hypersonic vehicle for optimum configuration. The developed method is subsequently applied for the study of receptivity to free stream acoustic disturbances over a blunt cone for the hypervelocity flow. Simulations with thermochemical nonequilibrium (termed as 'real gas simulations') and with frozen chemistry and thermal degrees of freedom (termed as 'ideal gas simulations') are compared. Second mode instability was observed for both ideal and real gas simulations. Real gas effects increased the range of unstable frequencies. For lower frequencies (where 2nd mode instability was not observed), real gas effects were found to have destabilizing effects. For higher frequencies (where nd mode instability was not observed), real gas effects tend to stabilized the flow. For the frequency for which real and ideal gas both predicted second mode growth, the growth rate for ideal gas simulations was greater. The location of instability was about the same for ideal and real gas cases. The average of unstable frequencies for real gas simulations was lower than the unstable frequency for ideal gas simulations. Overall, the real gas effects in present study lead to a more unstable boundary layer in terms of second mode instability.