Characterizing the operability limits of the HyShot II scramjet through RANS simulations

Experimental and flight data for hypersonic air-breathing vehicles are both difficult and extremely expensive to obtain, motivating the use of computational tools to enhance our understanding of the complex physics involved. One of the major difficulties in simulating this regime is the interaction between combustion and turbulence, both of which are intrinsically complex processes. This work represents a first attempt at addressing assumptions introduced by physical models representing the turbulent reacting flow on the resulting predictions of the scramjet performance. A combustion model for high-speed flows is introduced and tested for the HyShot II vehicle. A reduced order chemistry model is then derived to investigate the effect of certain chemistry modeling assumptions within the combustion model. These models are used to investigate the unstart of the engine due to thermal choking by increasing the fuel flow rate. It is shown that an abrupt change occurs where a normal shock forms and moves upstream accompanied by a large region of subsonic flow. Additionally scalar metrics are described which are used as early indicators of unstart, to formulate safe operating limits for the scramjet engine.