Numerical simulations of laser energy deposition for supersonic flow control

This thesis deals with the computational study of localized laser energy deposition in supersonic flows. This study is part of an effort to develop dynamic flow control mechanisms which can tackle critical flow conditions occurring due to shock-shock interactions in high speed flight. A model for Nd:YAG laser energy deposition in air has been developed for the purpose of this study. It was designed to predict the fluid dynamic effects of the energy deposition process in supersonic flows. The numerical model captures the key physical processes, including inverse bremsstrahlung absorption, evolution of the plasma shape and structure, air breakdown chemistry and the subsequent fluid dynamics. The model was validated and its constants were calibrated using measurements of experiments performed in quiescent air. The calibrated values of the model constants were found to accurately predict the energy absorbed by the laser spark for the different focal lengths of the converging lens; over a range of incident laser pulse energies and ambient pressures. The numerical model for energy absorption was used to deposit energy in supersonic flows. The supersonic flows considered were simplified models which mimic critical flow conditions encountered by a high speed air vehicle. First, the effects of energy deposition in three-dimensional supersonic flow past a sphere and a flow with Edney Type IV shock-shock interaction were studied. The energy deposition was found to be effective in reducing the peak surface pressure, but not as effective in lowering the surface heat transfer rate. Next, the effect of laser energy deposition on the Mach reflection of two symmetric crossing shock waves in the dual solution domain was studied. Various flow configurations (Mach number and shock angle) were considered for the energy deposition. The simulations showed that the perturbation brought about by the spark led to a transition from Mach reflection to regular reflection for certain flow configurations. Multiple sparks were used to increase the degree of perturbation for cases where no transition occurred due to a single spark. This resulted in a further reduction in the dimensions of the Mach stem, but did not lead to transition.