Evidence of non-thermal plasma effect for supersonic drag reduction

Summary form only given, as follows. Recent experiments conducted in a Mach 2.5 wind tunnel have demonstrated significant plasma effect on shock waves. The plasma acted as a spike, which effectively deflected the flow in the upstream region, and accounted for the observed non-thermal plasma effect on the structure of the shock wave. The plasma effect on the shock wave is further explored experimentally. A 30/spl deg/ half-angle truncated cone is used as the model with a protruding central-electrode isolated from the body for electric discharges. This experimental design enables the model to generate a weak conic shock attached to the tip of the central-electrode, and a strong bow shock located behind the weak conic shock and attached to the nose of the cone in the supersonic flow. It can also use an on-board discharge to produce plasma between two shock waves. The results show that the introduced plasma spike has drastically modified the original complicated shock structure to a simple one manifesting a single conic shock. In each discharge a significant drag reduction, which reduces wave drag by more than 50%, has been measured. This experiment demonstrated that an introduced plasma spike can improve the performance of a small physical spike, which otherwise, has no significant influence on the effective aerodynamic shape of a model. The results also show that the plasma effect on the shock structure lasts much longer than the discharge period. A thermocouple probe measures the gas temperature on the conic surface of the model. It is shown that during each discharge the gas temperature does not increase significantly to account for the observed plasma effect on the shock wave.