Investigation of the performance characteristics of a plasma synthetic jet actuator based on a quantitative Schlieren method

A quantitative Schlieren method is developed to calculate the density field of axisymmetric flows. With this method, the flow field structures of plasma synthetic jets are analysed in detail. Major performance parameters, including the maximum density increase behind the shock wave, the expelled mass per pulse and the impulse, are obtained to evaluate the intensity of the shock wave and the jet. A high-density but low-velocity jet issues out of the cavity after the precursor shock wave, with a vortex ring at the wave front. The vortex ring gradually lags behind the center jet during the propagation, and its profile resembles a pair of kidneys in shape. After the jet terminates, the vortex ring breaks down and the whole density field is separated into two regions. In one period, the jet front velocity first increases and then decreases, with a maximum value of 270 m s^-1. The precursor shock wave velocity decays quickly from 370 m s^-1 to 340 m s^-1 in the first 50 μs. The variation in the maximum density rise behind the precursor shock wave is similar to that of the jet front velocity. The averaged exit density drops sharply at around 50 μs and then gradually rises. The maximum mass flow rate is about 0.35 g s^-1, and the total expelled mass in one period occupies 26% of the initial cavity gas mass. The impulse produced in the jet stage is estimated to be 5 μN s^-1. The quantitative Schlieren method developed can also be used in the research of other compressible axisymmetric flows.