Characterization of plasma synthetic jet actuator with Laval-shaped exit and application to drag reduction in supersonic flow

Abstract

A plasma synthetic jet (PSJ) actuator (PSJA) with a Laval-shaped exit is investigated using a numerical method alongside a PSJA with a straight-shaped exit for comparison. The accuracy of the numerical method is first verified by comparing simulation results with experimental schlieren images and pressure measurement values. The performance of the PSJA with the Laval-shaped exit is then investigated in quiescent air. The results show that when the dimensionless energy ε > 5.06, the maximum exit velocity of the PSJA with the Laval-shaped exit becomes supersonic and is higher than that of the actuator with straight-shaped exit. The opposite is true when ε ≤ 5.06. The jet front velocity of the PSJ is much lower than the exit velocity, and no obvious improvement is seen when changing from the straight-shaped exit to a Laval-shaped exit due to the shock waves near the exit. Finally, the drag reduction effect of an opposing PSJ on a hemisphere in Ma3 flow is investigated. For a geometrically fixed PSJA, the flow field of a singled-pulsed opposing PSJ in Ma3 flow can be classified into three patterns according to the values of the maximum pressure ratio and ε: pattern 1 consists of only vortices and a slight change in the bow shock, pattern 2 consists of a typical long penetration mode (LPM) of the opposing PSJ, and pattern 3 consists of both a short penetration mode and a LPM. For PSJAs with both kinds of exits within a certain range, the average drag reduction increases with ε. However, when ε is higher than 48.02 for a Laval-shaped exit and 16.01 for a straight-shaped exit, the drag reduction effect decreases due to the rise in drag associated with the formation of the PSJ. The drag reduction effect associated with a PSJA with a Laval-shaped exit is significantly better than that of one with a straight-shaped exit when ε > 8. The optimal average drag reduction values, 25.82% and 20.55%, are obtained at ε = 48.02 and ε = 16.01, respectively, for a Laval-shaped exit and a straight-shaped exit.