Performance Characteristics Of Sparkjet And Its Application On Shock Wave Control

Efficacious flow control methods have important application value and can improve the aerodynamic performance of aircraft, which can enable safe and maneuverable flight. “Sparkjet”(also called a “plasma synthetic jet” or “pulsed-plasma jet” by other researchers) is a new type of plasma aerodynamic actuation and is attracting more and more researchers’ attention.The application of sparkjet to flow control system is based on the sparkjet actuator’s design level and work performance and the actuator orifice design and ambient pressure are two important influencing factors of sparkjet actuator’s work performance. Sparkjet actuator combines the technical advantages of both synthetic jet actuator and plasma aerodynamic actuator and overcomes the difficulty of inducing air flow at a high speed, which leads to its good application prospect in high speed flow control.In this paper, experimental and numerical methods are used to investigate the performance characteristics of sparkjet issuing into stagnant air as well as supersonic flow and its application in shock wave control. The main work is summarized as follows:(1) To study the performance characteristics of sparkjet issuing into stagnant air, a phenomenological simulation built by a single energy deposition is accomplished by equating the physical effects of the spark discharge with gas Joule heating and adding source term in energy equation. The kinetic energy and heat injection into outer flow field of plasma synthetic jet are used as characterizations of “impact effect” and “thermal effect”. The results show that the kinetic energy and heat injection of plasma synthetic jet are mostly concentrating in primary jet during the self-sustained oscillation process established by a single discharge and “thermal effect” of jet works longer than “impact effect”. Overall energy efficiency of spark actuator is about 2.3% at 1atm. Furthermore,the influence of different actuator orifice shapes and ambient pressure are studied.(2) The interaction of sparkjet with the supersonic crossflow is investigated and the results show that spark discharge synthetic jet can cause separation and reattachment in the supersonic flow and relatively strong bow shake waves are generated. The upstream separation length and strength of shake wave increase at first and then decrease as jet spouts out. The shake wave is bow-shaped at the beginning and gradually becomes oblique as it weakens.The jet-to-crossflow momentum flux ratio and interaction effect increase greatly as discharge energy rises.(3) The control effect on oblique shock wave by three-electrode sparkjet actuator is investigated experimentally. The sparkjet is injected normally into a Mach 2 crossflow and the control effect is observed using high speed shadow technology. The results show that the oblique shock wave generated by a 25° compression ramp can be weakened and even eliminated partly and the action time is about 230μs.(4) In order to overcome the refill difficulty of sparkjet actuator in supersonic flow discovered by preceding study, a new dynamical pressure type sparkjet actuator is investigated and optimized. The results show that the new type actuator can increase the refill speed by 85% and its performance is more robust.