Non-Equilibrium Thermochemistry in Hypersonic Expanding Flows

Hypersonic vehicles, which travel at over 4,000 miles/hour, induce complex flow physics. The resulting production of extreme temperatures ultimately affects their aerodynamic controllability and requires advanced thermal management. At hypersonic speed, a strong shock is generated in front of the vehicle, which compresses the surrounding atmospheric gas to temperatures exceeding 5000 degrees C. This results in high temperature gas effects, such as dissociation and even ionisation. This gas can then be expanded around the vehicle and into its wake. The reduction in temperature taking place across the expansion fan slows down electron capture and recombination reactions. As a result, large
amounts of excited atomic species, produced in the post shock region, survive into the shock layer surrounding the vehicle, or into its wake, thus, creating a state of thermo-chemical non-equilibrium.

The presence of extensive regions of non-equilibrium flow makes the aerothermodynamic characteristics of the vehicle more difficult (and computationally expensive) to predict. The challenges imposed by expanding non-equilibrium flow often have undesirable consequences on engineering practice. This can result in the need for increased safety factors in the design of thermal protection systems, particularly for the rear of the vehicle - a further cost factor and design challenge in producing viable hypersonic vehicles. As the flow is coupled to the thermochemistry, it can also lead to changes in the aerodynamics of the vehicle and operation through control anomalies. This is due to changes in skin friction, boundary layer transition and separation. Extensive areas of non-equilibrium flow also affect other aspects of atmospheric missions flown at hypersonic speeds, including a decrease in the observability of the vehicle from mission control and a block of optical transmission.

There has been little research performed on these expanding high temperature gases. The proposed research...