Applications of Plasmas to Modify Shocks in Supersonic Flows

Considerable effort is currently focused on the possibility of using plasmas in air as a novel means of controlling the aerodynamic characteristics of vehicles flying at hypersonic speeds. Of special interest is the effect of weakly ionized plasmas on theflow of regions with intense dissipation such as shock waves and boundary layers. In a Phase I program we have explored the effect of low-pressure nonequilibrium plasmas on low- Mach-number shock waves. Methods were developed for accurately measuring boththe shock-wave flow field and the electrical characteristics of shock waves propagating in these types of discharges. Large dispersion of the shock waves and increases in speed were observed, while thermal effects were minimized. The plasma-generationtechniques developed in the Phase I program will be modified in Phase II to work at higher pressure and in larger gas volumes. Plasma-generation methods such as DC discharges, different types of rf excitation, externally ionized plasmas, and dielectricbarrier discharges will be considered. Analytical and diagnostic methods will be refined, especially using optical methods to obtain more detailed measurements of the resulting shock structure and to improve the understanding of physics of the shockwave-plasma interaction. Based on the results of Phase II, this technology can be extended to establish design parameters that are scalable to actual flight test vehicles. The plasma-generation techniques developed for shock-wave remediation may also bedirectly applicable for improving supersonic combustion.