On the use of plasma for shock wave mitigation.

摘要

An experimental study on the influence of on-board generated plasma on shock waves structures and blunt body aerodynamics in a supersonic flow is presented. A slender physical spike, axially protruding forward, was used as the cathode for on-board discharge to generate plasma in front of a 60° truncated cone-cylinder (used as the anode) immersed in a Mach 2.5 non-ionized flow. Measurements of the discharge current and voltage, as well as of the flow pressure and temperature at the surface of the object were performed. Simultaneous shadow/Schlieren and plasma glow imaging techniques were used for flow visualization and characterization. It is found that plasma generated in front of the model had a very significant effect upon the shock wave structure when the slender spike had a proper aspect ratio. A change from a detached bow shock to a tip attached conical shock wave was observed. This is equivalent to a favorable increase by about 70% in the body aspect ratio, from a blunt body to a conical one, as also evidenced by the pressure changes. In each discharge, which lasted about 40 msec, the energy consumed was about 150 J. The frontal pressure dropped by more than 30%, while the pressure on the cone surface of the model increased only by about 5%. The importance of the aspect ratio rather than the discharge power on the observed phenomenon suggests that the thermal effect (induced by the plasma) on the shock wave structure is minimal. In front of the model, the plasma glow distribution did not follow the newly formed conical shock wave pattern, but rather a conical shape of much smaller angle starting at the spike tip. Plasma effects upon the flow aerodynamics around the model, including changes and transformations of the boundary layer and expansion waves, were also investigated through the plasma afterglow intensity distribution. The reported experiments demonstrates that the influence of a small physical spike on the body aerodynamics can be greatly improved by generating plasma around it to form a plasma aero-spike.