Principle Of Plasma High-energy Synthetic Jet And Supersonic Flow Control

Efficient methods of high speed flow control can provide enhanced propulsive efficiency and at the same time enable safe and maneuverable high speed flight, but the practical application of active flow control is dependent upon the development of robust actuators. Because of the advantages of simplicity, fast response, sufficient bandwidth,no moving part and robustness, plasma aerodynamic actuators have been became the front subiect and focal point in flow control and fluid dynamic fields. As one kind of plasma aerodynamic actuators, the plasma synthetic jet(PSJ) actuator has the characteristic of zero mass flux of synthetic jet actuator, which requires no flow supply and no flow piping, and has all of the advantages of plasma actuator as well. The plasma synthetic jet actuator can produce a high energy plused jet and a strong “precursor shock”,it appears that PSJ actuators have considerable potential for further research into high-speed flow control, and become the breakthrough for the transfer of the high speed active flow control technology from laboratory to a practical engineering application.In order to improve the performance of the PSJ actuator and make the high speed flow field to be controlled efficiently, a PSJ actuator has been investigated throughly in this dissertation, and a novel three-electrode PSJ actuator and its application in high speed flow control are studied by means of numerical simulation, experiment and theoretical analysis.Based on the thermal effect of gas discharge in the working process of the PSJ actuator, and combine the assumption of local thermodynamic equilibrium plasma, a phenomenological energy deposition model of the PSJ is established. The flow field evolution process and the jet velocity characteristic of the PSJ during a whole cycle are analyzed,.an important actuator parameter-saturated frequency is proposed. The simulation results shows that during the working process of the two-electrode PSJ actuator, the fractions of electrical energy that goes into gas heating and jet kinetic energy are about5% and 1.6% respectively. The fast flow field response capacity of the PSJ actuator is verified experimentally. For the two-electrode PSJ actuator supplied by a capacitive power, the fraction of the capacitior energy transfers to arc energy is about 20%. The diameter of the jet exit and the cavity volume has important influence on the flow characteristics of the PSJ. As the increasment of the discharge frequency, the influence of the frequency on the PSJ performance slows down.By introducing a trigger electrode in the two-electrode PSJ actuator structure, and modifing the actuator electrical source, a novel three-electrode high energy PSJ actuator is designed. The three-electrode PSJ actuators can effectively reduce the breakdown voltage, minish the volume and power of the electrical source, making the actuator system easy to be miniaturized and integrated. When the breakdown voltage is fixed, thethree-electrode actuator can increase the arc length, making the cavity gas heated sufficiently and enhancing the performance of the produced jet. Compared with the two-electrode actuator, the fraction of the capacitor energy transfer to arc can be increased to about 80%. As the input capacitor eneergy is same, the three-electrode PSJ actuator can produce a higher velocity jet and a stronger “precursor shock”, so the three-electrode actuator has the advantages of low energy consumption and high energy efficiency. The ratio of the arc energy and the intial cavity gas energy is the important influence factor for the flow characteristic of the three-electrode PSJ actuator.The characteristic of the two/three electrode PSJ actuators at different low pressure envirnment have been comparativly studied, the flow field structure and the parameters influence law of the three-electrode PSJ actuator are analyzed. The results show that the breakdown voltage and peak discharge current for the two/three electrode actuators decrease with decreasing environment pressure, but the fractions of the capacitor energy transfer to arc are invariable, and maintain for about 20% and 85% for two different actuators respectively. The peak jet velocity reaches the maximum at p=0.1atm and0.6atm for the two-electrode PSJ actuator, but the “precursor shock”velocity is constant and is about 345m/s. The velocity of the precursor shock and plasma jet is almost unmodified by the ambient pressure conditions for the three-electrode PSJ actuator, and the strength of the “precursor shock”reaches maximum at 0.6atm. As the capacitance increases, the transfer efficiency of the capacitor-arc energy decreases, the velocity of the plasma jet and the “precursor shock”decay increases with increase in capacitance and decrease in cavity volume.The interaction of the plasma high energy synthetic jet with the supersonic crossflow is investaged, the vortex/wave flow control mechanism of supersonic flow for the PSJ is proposed and experimentally validated, and the influence law upon control effect for the shok is discovered. In a Ma2 crossflow, the maximum influence from the plasma high energy synthetic jet is nearly as effective as the steady microjets at a microjet pressure ratio of 3.2, and the maximum momentum flux ratio of the jet compared to the freestream is about 1.1. In the supersonic crossflow, the interaction shock produced by the plasma jet has the effect of reduce the pressure difference before and after the controlled shock, and to realize the shok control mechanism. The high temperature jet near the boundary can entrain the high momentum fluid into the boundary layer and has heat congestion effect on the mainflow, so as to change the shock angle and reduce the shock strength based on vortex contol mechanism. The plasma jet placed upstream of the separation shock has better effect on the shock control, and the control effect decreases with jet pitch angle decreasing.