Pseudoshock Morphology and Dynamics Under Active and Passive Flow Control

Pseudoshocks are shock wave structures that are generated when supersonic internal flows are subjected to a downstream pressure increase. Pseudoshocks often arise within high-speed air-breathing engines due to the pressure rise caused by combustion. Inherent unsteadiness, nonuniformity, and sensitivity to flow conditions has motivated significant research efforts towards understanding pseudoshocks. This work addresses two aspects of pseudoshock physics. Firstly, a reduced-order model for predicting pseudoshock outlet characteristics is developed. Secondly, active and passive methods for pseudoshock control are experimentally investigated. Many reduced-order models have been developed for pseudoshock predictions. The current state-of-the-art methods model pseudoshock flows with a core region of constant Mach number and displacement region of zero Mach number. This simplification has resulted in disagreement between models, particularly for Mach number and total pressure predictions. This research develops an adaptive control volume method which accounts for flow separation, Mach number nonuniformity, and turbulent stresses. The new model is compared to Reynolds-Averaged Navier-Stokes simulations and indicates good agreement for outlet flow predictions. A sensitivity analysis reveals the dependency of the model accuracy to physical phenomena. Electrical gas discharge is a method of active shock control that has been demonstrated in various flow configurations. Past studies have focused on using electrical discharges to reposition reflected shocks. This work extends the flow control method to Mach 2 pseudoshocks. Experiments indicated that electrical gas discharges modified the pseudoshock by introducing asymmetry and reducing the size of normal shocks within the structure. Oscillations on the order of 100 Hz were observed during flow control. Application of the adaptive control volume model indicated that the flow control reduced total pressure losses when the pseudoshock was sufficiently short. Passive slots have been shown to anchor and shorten the pseudoshock over a range of downstream pressures. Although this effect has been demonstrated in many experimental and computational studies, the unsteady dynamics of the pseudoshock under control is not well understood. The present work describes the dynamics of a pseudoshock in a continuous-running Mach 2 tunnel during interaction with passive 45 degree slots. It was observed that the control effect was sensitive to the pseudoshock position and the on-design slot condition. A moderate anchor condition was identified and shown to dampen pseudoshock oscillations. A strong anchor condition was identified and shown to introduce a high-amplitude 30 Hz oscillations. Additionally, the slots stabilized the pseudoshock structure in the presence of distortion, where the uncontrolled pseudoshock was observed to stochastically "flap" between the tunnel walls.<p></p>