Experimental Study Of Surface Dielectric Barrier Discharge Plasma Actuator For Airflow Control

Plasma flow control technology generally refers to an controllable disturbances to the flow field through airflow acceleration induced by the plasma in the electromagnetic field or some changes in temperature, pressure, as well as some stickiness, heat transfer characteristics of the gas produced in the electrical discharge process. Plasma airflow control is a kind of novel active airflow control technology, which has some specific features such as simple mechanism with no moving parts, easy to apply without changing the existing aerodynamic structure, low power consumption and fast responsibility. It has board application prospect on improving the aerodynamic performance of the aircrafts. Surface dielectric barrier discharge (SDBD) plasma actuator, which is the most common used plasma airflow control device, has been receiving overwhelming attention for more than a decade. The SDBD plasma imparts an electro-hydro-dynamic (EHD) body force on the ambient air inducing a tangential flow acceleration, or so-called ionic wind, through collisions between drifting ions and ambient neutral molecules making it possible for the airflow control applications.Usually, the velocity of the induced ionic wind by a SDBD plasma actuator can reach several m/s, which limits its practical applications. So, optimization of the plasma actuator is needed to improve the EHD performance for the practical applications. Meanwhile, the further exploration on the EHD mechanism is also needed to provide theoretical guide for performance optimization. The electric charge accumulation on the SDBD plasma actuator is an important factor that affects the behavior of the SDBD plasma and its EHD performance. This thesis is mainly focused on the electric charge factor in the SDBD plasma actuator and its effect on the EHD performance. To improve the SDBD plasma actuator performance and investigate the mechanism of the EHD effect, the following work has been done in this thesis:1. The experimental platform is established for the SDBD plasma actuator for airflow control. A stable layer of plasma can be generated along the actuator surface in the open air. The discharge and aerodynamic characteristics of the SDBD plasma actuator can be experimentally investigated. A new kind of surface potential probe system for the SDBD plasma actuator is designed. As an AC high voltage is applied to the encapsulated electrode to generate the discharge plasma, corona discharge appears on the needle tips through capacitive coupling to form a weakly conducting channel between the needle tips and the dielectric surface. Thus the corona discharge can make the potential measuring circuit closed. Then the surface potential signal can be detected by a high-voltage probe and recorded by a digitizing oscilloscope. High measuring accuracy and fast response ability can be achieved through the impedance matching circuit. The measurement of the surface potential special distribution can be obtained through a scanning process with the help of a computer controlled moving equipment. Compared with the commercialized electrostatic voltmeter, this probe system has some advantages such as high-voltage resistance, high special resolution, fast response ability and easy to apply.2. The effect of a DC bias on the EHD force induced by a surface dielectric barrier AC discharge actuator for airflow control at the atmospheric pressure is investigated. The measurement of the surface potential due to charge deposition at different DC biases is carried out by using a special designed corona discharge potential probe. From the surface potential data, the plasma electromotive force (EMF) is shown not affected much by the DC biases except for some reduction of the DC bias near the exposed electrode edge for the sheath-like configuration. The total thrust is measured by an analytical balance, and an almost linear relationship to the potential voltage at the exposed electrode edge is found for the direct thrust force. The temporally averaged ionic wind characteristics are investigated by Pitot tube sensor and schlieren visualization system. It is found that the ionic wind velocity profiles with different DC biases are almost the same in the AC discharge plasma area, but gradually diversified in the further downstream area as well as the upper space away from the discharge plasma area. This is perhaps because that the DC bias applied at the upper electrode can not effectively enhance the potential gradient in the high density plasma region due to the conductivity of the plasma but can enhance the potential gradient in the further area beyond the plasma region where the ion density is relatively lower leading to a limited EHD performance increment.3. The characteristics of a plate-to-plate AC surface dielectric barrier discharge (SDBD) actuator using pulse induced breakdown enhancing method is experimental investigated. The encapsulated electrode is supply with the sine AC high voltage while the exposed electrode is feed by a synchronized pulse voltage. A parametric study is performed based on the thrust force and power consumption measurements in which the thrust force was observed to be increased by about 100% to 300% and the efficiency increased up to about 100% compared with the AC-only supply conditions for different AC voltage within the tested range when the positive pulse applied at the trough phase of the AC cycles. The pulse induced breakdown effect is analyzed from the electrical and light emission waveforms to reveal the mechanism underneath. And the surface potential due to charge deposition effect is also measured using a special designed corona like discharge potential probe. It is shown that the pulse induced breakdown could cause a temporary intensified local electric field to enhance the glow-like discharge and meanwhile increase the time-average surface potential in the further downstream region. The force improving effect by pulse induced breakdown enhancement was mainly due to the glow-like discharge enhancement and the surface potential increment, with the latter is more important when the AC voltage is higher.