Influence of shock waves from plasma actuators on transonic and supersonic airflow

Abstract

This paper presents experimental and numerical investigations of high-current sliding surface discharges of nanosecond duration and their effect on high-speed flow as plasma actuators in a shock tube. This study deals with the effectiveness of a sliding surface discharge at low and medium air pressure. Results cover the electrical characteristics of the discharge and optical visualization of the discharge and high-speed post-discharge flow. A sliding surface discharge is first studied in quiescent air conditions and then in high-speed flow, being initiated in the boundary layer at a transverse flow velocity of 50–950 m s−1 behind a flat shock wave in air of density 0.04–0.45 kg m−3. The discharge is powered by a pulse voltage of 25–30 kV and the electric current is ~0.5 kA. Shadow imaging and particle image velocimetry (PIV) are used to measure the flow field parameters after the pulse surface discharge. Shadow imaging reveals shock waves originating from the channels of the discharge configurations. PIV is used to measure the velocity field resulting from the discharge in quiescent air and to determine the homogeneity of energy release along the sliding discharge channel. Semicylindrical shock waves from the channels of the sliding discharge have an initial velocity of more than 600 m s−1. The shock-wave configuration floats in the flow along the streamlined surface. Numerical simulation based on the equations of hydrodynamics matched with the experiment showed that 25%–50% of the discharge energy is instantly transformed into heat energy in a high-speed airflow, leading to the formation of shock waves. This energy is comparable to the flow enthalpy and can result in significant modification of the boundary layer and the entire flow.

Visualization of the interaction region of an oblique shock wave with a boundary layer by the radiation of a nanosecond surface sliding discharge

“…The experiments were carried out using a shock tube with a low-pressure chamber with a length of 3 m, a rectangular channel with an internal cross section of 24´48 mm 2 , and a discharge chamber of the same cross section (Fig. 1 a) [9,12]. Supersonic air flows were created behind plane shock waves with Mach numbers 2.8-4.2.…”

“…The Reynolds number of the flow was ~ 10 5 , estimated from the size of the shock tube channel. The thickness of the laminar boundary layer on the channel walls did not exceed 1 mm [9,12].…”

“…The main energy input to the gas occurs within 120-150 ns of the first half period of the discharge current, i.e. almost instantaneously as compared with the characteristic gasdynamic flow times in the boundary layer [9,12]. The electric field applied to the discharge gap was E = 8.33 kV/cm, and the reduced electric field E/N under the experimental conditions reached 3 •10 -19…”

“…The usage of low-temperature plasma of surface discharges of various types (plasma actuators) in plasma aerodynamics is aimed to correct the flow regime, including the reduce of dynamic and thermal loads on the surface, controlling the laminar-turbulent transition in the boundary layer, the position of separation zones and shock waves [8][9][10], and the processes of combustion [11]. Pulsed distributed surface sliding discharge of nanosecond duration (plasma sheet) can be used as an actuator to influence the flow [9]. It consists of channels sliding along the dielectric surface and forming a plasma layer comparable in thickness with the boundary layer of a supersonic flow in a shock tube (~ 0.5 mm).…”

Динамика Излучения Наносекундного Поверхностного Скользящего Разряда В Потоке С Ударной Волной

“…Изучение взаимодействия потоков газа с плазменными образованиями связано с задачами плазменной аэродинамики и остается актуальным на протяжении последних десятилетий [1][2][3]. При помощи поверхностных разрядов разного типа (плазменных актуаторов) можно реализовать энерговклад в пристеночную область течения газа, контролируя ламинарно-турбулентный переход в пограничном слое, положение зон отрыва и скачков уплотнения вблизи обтекаемой поверхности [1].…”