Studies of the transient flows in high enthalpy shock tunnels

The nature of high enthalpy shock tunnels dictates that only very limited run time can be achieved during experiments. Due to the extreme flow conditions and the severe time constraint involved, it is very difficult to conduct diagnostic measurements to determine the flow condition produced in the facilities. A series of numerical studies has therefore been carried out to provide a quantitative description of the transient flow in the shock tunnel. The flows in the HEG shock tunnel are analyzed using time-dependent viscous computations. The studies focused on the events subsequent to shock reflection at the downstream end of the shock tunnel, namely, the reservoir and the nozzle regions. For the shock tube, the interactions of the reflected shock with the wall boundary layer and the contact surface are examined for their contribution to driver gas contamination and the generation of flow disturbances. This includes interaction with the reflecting wall geometry, that is, in the presence of the nozzle entrance and "particle stopper". For the starting flow in the nozzle, the propagation of the initial shock system and the development of the boundary layers during the starting transient are examined and the time required to established the steady flow is analyzed to help determine the proper "test window" in the experiments.