Novel Plasma Synthetic Jet And Its Application In Shock Wave Control

Flow control technology is of great application value to human beings.Driven by various military and economic demands,flow control technology has obtained increasingly success in recent years,under the guidance of scientific theories and with the development of micro-electro-mechanical system,material science and computational fluid dynamics.At the beginning of this century,with the success of flight tests of X-43 A et al.,the research of hypersonic vehicle entered the stage of rapid development.As a key point of technical breakthrough of hypersonic vehicle,the research and exploration of new flow control technology,especially high-speed active flow control technology,is of great significance.Fluidic actuator(including of zero and non-zero mass flow jet)and plasma actuator(represented by dc glow discharge plasma actuator)are the two most popular types of high-speed active flow control actuator.The study of two kinds of actuator has accumulated rich achievement.Plasma synthetic jet(PSJ)actuator is the combination of these two kinds of actuator.Because PSJ has the advantages of both fluidic actuator(high induced jet speed and strong penetrating)and plasma actuator(fast response,no moving parts or fluid supply device and wide frequency band),it shows a good application prospect in the field of high-speed flow control.It is very likely to be a breakthrough for high speed active flow control technology from laboratory to practical engineering application.In order to promote the practical application of PSJ,this paper carried out the investigation of PSJ actuator and its flow control performance on shock wave control in the supersonic/hypersonic flow by using experimental method mostly combined with certain theoretical analysis and numerical simulation.The related research were carried out in view of three major application problems: energy efficiency problem(long actuation duration problem),collaborative array problem(large space scale actuation problem)and adaptability problem in the high altitude rarefied air environment(wide actuation field problem).In order to realize the long working time of the actuator and reduce the volume and weight of the power supply system,the complete energy transfer process analysis and energy efficiency calculation of PSJ actuator were carried out.The total energy efficiency of typical working conditions was about 11.3%,among which discharge efficiency,heating efficiency and exhaust efficiency was 40%,64% and 44.2% respectively.Since the discharge process was located at the upstream of the energy transfer path,the loss caused by additional resistance was relatively significant.In the energy composition of PSJ,the heat energy of the jet flow occupied the main body,accounting for over 90%.The parameter matching of "large electrode spacing and small capacitance capacity" was helpful to improve discharge efficiency and heating efficiency.Research on the working characteristics of a novel self-pressurizing opposing PSJ actuator,as well as its blunt body shock wave control and drag reduction characteristics,were carried out for the first time.Different from the static or transverse jet actuator,opposing jet actuator could produce strong multi-jet flow after one discharge,which was conducive to extending the excitation time of one discharge.Due to the different actuation range,there were two typical interference modes between PSJ and blunt body shock: local prominent and global covering modes.The effective drag reduction of the blunt body was achieved.The peak drag reduction rate of the blunt body was about 70% in a Mach 3 flow,and the maximum drag reduction profit of single discharge was about 5.35 J.The shock control characteristics of transverse PSJ actuator were studied.The pressure time history of the compression ramp wall surface wave was obtained by using high-frequency dynamic pressure measurement for the first time.The shock wave was significantly weakened by low-frequency high-energy PSJ.The pressure of the compression ramp wall surface was reduced by up to 79% in a Mach 3 flow.The unsteady motion of the shock wave was modulated by 2500 Hz high-frequency small-energy jet.The motion amplitude of controlled shock wave was increased by 3.6 times.The shock control experiments of PSJ actuator in the hypersonic flow were carried out for the first time.The Mach number of the freestream was 5.For opposing PSJ actuator,due to the stagnation of hypersonic flow in the head,the actuator had the selfpressurizing characteristics,so the same actuator configuration in the supersonic flow field was used.The results showed that the opposing PSJ actuator could continue its good control characteristic as Mach number increases.And because the stand-off distance of the head shock decreased with the increase of Mach number,PSJ actuator obtained a more significant effect on the increase of the shock stand-off distance.The shock stand-off distance increased by about 4.6 times(which is only 3.2 times in the Mach 3 flow)at the moment of the strongest actuation.In order to overcome the problem of low-static pressure environment in hypersonic flow field,two new types of transverse PSJ actuators(air collector pressurized actuator and ram-air actuator)with different pressurization methods were designed based on the idea of the integration utilization of hypersonic flow energy.The original rational experiments of the PSJ actuator in a low-pressure chamber showed that the cavity pressurization increased the actuator control authority significantly.The jet peak speed increased from 256 m/s to 507 m/s.Hypersonic wind tunnel experimental results showed that with a 82 kPa air supply pressure,PSJ decreased the shock wave angle of a 25 degrees compression ramp by about 3 degrees.Ram-air actuator experiment results showed that the cavity pressurization ratio was about 4.72 and 7.69 times respectively for the actuator with 0 mm and 6 mm height step.As the separation shock wave and the backward ramp reduced the mainstream velocity around the jet exit,the penetration of PSJ and its interference effect on the mainstream were significantly enhanced.The operation of two-electrode PSJ actuator serial/parallel array was realized.For serial actuator array,the power supply was simple and easy to be miniaturized.The discharge efficiency was basically the same as that of a single actuator.The air breakdown mechanism of the serial array was derived from the induction of the pre-weak-discharge between the energized electrode and the suspending electrode.The breakdown voltage of the serial array depended on the sum of the air gap length.As the actuators became closer,the entrainment effect increased and the velocity of PSJ increased.For parallel actuator array,the open and close state,the working frequency and the working phase of each actuator etc.could be controlled individually.Its control characteristic was more flexible,and the actuation effect was more controllable.Moreover,the working of parallel actuators with different phase could overcome the "saturated frequency limit" caused by the slow refill rate,realizing the multiplication of the excitation frequency.