Unsteady shock-wave reflection and interaction in viscous flow with thermal and chemical nonequilibrium

Numerical simulations were used to study steady shock/boundary layer interactions and self-sustained unsteady hypersonic type IV shock-shock interference heating problems with nonequilibrium real gas effects. The emphasis of the investigation was on the effects of internal thermochemical excitation on surface heating rates, skin friction, and flow field unsteadiness of the viscous shock interactions. The multicomponent Navier-Stokes equations with nonequilibrium rotational, vibrational, and chemical models for five-species air were solved using a finite-volume, second-order TVD scheme together with a new third-order semi-implicit Runge-Kutta scheme. For a steady shock/boundary layer interaction on a flat plate, it was found that the real gas effects reduced the size of the shock induced separation bubble and the magnitude of the surface heating rates. For the shock-shock interference flow of nitrogen over a cylinder at Mach 8, the results showed that type IV shock-shock interference heating flows with real gas effects were inherently unsteady. The degree of the unsteadiness was related to the location of the jet impingement on the cylinder relative to the stagnation point. For certain impingement positions, vortices were generated and shed off near the jet impingement point. This periodic shedding of the vortices contributed to the self-sustained oscillations of both the jet and other parts of the flow field. The effect of thermochemical nonequilibrium was observed to be a decrease in the peak surface pressure enhancement and an increase in peak surface heating enhancement, relative to a perfect gas flow of the same freestream conditions. The nonequilibrium cases exhibited a higher oscillation frequency and wider range of variation over a cycle than did the perfect gas flows.