A Computational Analysis of Hypersonic Store Separations

Many current hypersonic vehicles involve shrouds, fairings, boosters, or ejectable payloads separating during flight. It is imperative that they do not strike each other after separation as this typically results in damage or loss of vehicle. This requires a detailed understanding of the flow features involved such as shock waves, expansion waves, shock reflections, and shock wave boundary layer interactions influencing the vehicles' attitude and trajectory. Experimental and flight tests of these scenarios are costly and need massive infrastructure which require difficult measurement techniques to characterize the flow field. Alternatively, numerical simulations can provide accurate, low-cost, and efficient predictions of hypersonic separations.

This study looks at the scenarios of a smaller vehicle or store in the flow field of a larger vehicle. Computational fluid dynamics simulations are performed on a $7^\circ$ cone crossing an oblique shock wave at Mach 7 using NASA's OVERFLOW 2.3e Reynolds-averaged Navier Stokes solver. Trajectory and attitude is tracked along with capturing flow features and their imposed forces. The vehicle's dynamics when passing through a shock appears to predominantly the result of differential flow incidence angles causing a strong shock leading to a large pressure increase over a fraction of the vehicle which influences pitch. The vehicle appears to follow conventional longitudinal stability theory and becomes more stable during the interaction with the center of pressure moving aft and the peak pitching moment happening when the shock passes through the center of gravity if allowed to continue through the body. Complex shock wave boundary layer interactions are seen which could complicate specific separation scenarios. Nonphysical anomalies are seen in the flow field which are theorized to be the result of OVERFLOW's implicit solution algorithm but are shown to have little influence on results. Likewise, the applied forces and moments along with center of pressure in this scenario are shown to be unaltered by hybrid Reynolds-averaged Navier-Stokes and Large eddy simulations in the form of delayed detached eddy simulation.