A Study On Characteristics Of Surface Dielectric Barrier Discharge Plasma And Aerodynamics

Surface dielectric barrier discharge(SDBD)plasma,used as a new active airflow control technology,has some advantages such as its simple structure with no moving parts,low energy consumption,short response time and high excitation bandwidth.The plasma actuator for active airflow control at atmospheric pressure,has been a frontier research topic in the interdisciplinary research area of plasma dynamics and aerodynamics.The discharge directly transfers the momentum to neutral air by the collisions of energetic ions with neutral gas molecules to produce Electrohydrodynamic(EHD)force,and then induces the ambient-gas motion along the surface forming the "ionic wind".The "ionic wind" makes SDBD plasma actuator possess the ability of airflow control and its velocity can determine the mechanical performance.However,the velocity of "ionic wind" induced by SDBD plasma actuator is just within several meters per second,which limits the practical application of actuator.Thus,the current research is focused on the optimization and improvement of the plasma actuator to enhance EHD force and "ionic wind".Meanwhile,the further exploration on discharge characteristics and dynamics performance of SDBD plasma actuator under different conditions should be carried out to provide the valid theoretical guide for the reasonable optimization.To improve the mechanical performance of SDBD plasma actuator and understand the mechanism better,the following work is done in this paper:1.Four different electrode configurations,i.e.,plate aluminum foil,sharp blade,thin wire and dense copper mesh are chosen as exposed electrodes for the SDBD plasma actuator.The effects of the four structures with different materials,edge shapes,cross sections and layouts on the mechanical performance are experimentally investigated through measuring the current,power consumption,surface potential,"ionic wind" velocity,and mean thrust production.The result shows that the actuator with the copper mesh exposed electrode can generate the maximal induced force and spatial airflow velocity,while the actuator with the aluminum foil exposed electrode can generate the minimal induced force and spatial airflow velocity.This difference,as analyzed,is mainly due to the distinct discharge characteristics caused by the specifically designed exposed electrode configurations.This paper illustrates that the actuator with strong glow-like discharge in positive period and uniform discharge in negative period has preferable mechanical performance.2.A new electrode configuration,i.e.,a row of needle with high curve radius,is taken as an exposed electrode for the SDBD plasma actuator,and the electrode height is adjustable.The row of needle can induce an enough strong local electric field at the electrode edge and produce different spatial plasma distribution by adjusting the height.The effects of different electrode heights on the airflow acceleration behavior are experimentally investigated by measuring discharge image,surface potential distribution,ionic wind velocity,and mean thrust force production.It is demonstrated that the airflow velocity and thrust force increase with the exposed electrode height and the best actuator performance can be obtained when the exposed electrode is adjusted to an appropriate height.The difference,as analyzed,is mainly due to the distinct plasma spatial distributions and electrical fields at different exposed electrode heights.3.The above four types of actuators with different configurations of exposed electrode are still investigated.In this work,the four SDBD actuators are driven by dual-power supply,referred to as a fixed AC high voltage and an adjustable DC bias.The effects of DC bias on the dielectric surface potential distribution,plasma electromotive force distribution,spatial"ionic wind" velocity and the EHD force are studied,and the dominative factors of airflow acceleration behavior are revealed.The results show that the polar,amplitude and distribution of surface potential can be regulated by the DC bias,but different tendencies of surface potential present when the positive and negative DC biases are applied to actuators.The basic shapes of the potential profiles are quite similar when the positive biases are supplied to the exposed electrode,and the potential for the same position is shown to increase with the DC bias.Nevertheless,the potential profile shapes present a change when the negative biases are supplied to the actuator.The potential is shown to decrease slightly compared to the variation of negative DC biases,especially for the position near the exposed electrode.Different tendencies of surface potential for positive and negative DC biases demonstrate a sheath-like zone exists near the edge of exposed electrode,and the sheath-like zone is dependent on the geometry of the exposed electrode.In addition,the performance of the ionic wind produced by a single SDBD can be changed by DC bias.It is found that DC bias has little effect on the airflow velocity profiles in the discharge plasma area,however,it can significantly modify the airflow velocity profiles which are far away from the SDBD plasma area.It is suggested the potential gradient produced by DC bias doesn't work effectively in the plasma area due to the conductivity of the plasma,but can affect ion movement in the further downstream area beyond the plasma.The ion density is relatively lower in the area far away from plasma,which results in the limited EHD improvement.4.The SDBD plasma actuator with copper mesh exposed electrode is still driven by dual-power supply,referred to as an AC high voltage and a synchronized nanosecond pulse voltage.When the both have same frequency and the pulse voltage(positive or negative)is superimposed on some phases of AC signal,the pulse-induced breakdown in the rising edge is able to cause a temporarily intensified local electric field to enhance the glow-like discharge and increase time-average surface potential in the further downstream area.Meanwhile,the spatial airflow velocity and thrust force increase and reach the maximum when pulse voltage is superimposed at the trough of AC signal.Compared with the mechanical performance driven by a single AC voltage,the positive pulse voltage supplied at the trough phase of AC signal can increase the thrust by a factor of 2.5 and the efficiency up to a factor of 2,however,the negative pulse voltage supplied at the trough phase of AC signal just increase the thrust by a factor of 1.28 and the efficiency up to a factor of 1.18.Otherwise,the discharge characteristics and mechanical performance are measured when the pulse voltage is fixed at the trough of AC signal and the rate is gradually reduced.As a result,the pulse discharge current produced in the rising edge increases with the decreasing pulse rate,but this effect just strengthens the first glow-like discharge after the pulse voltage without influencing the other discharge cycles,and the time-average surface potential in the further downstream area decreases due to decreasing discharge pulse number.Thus,the thrust and efficiency decreases with decreasing pulse rate.We also report some obvious differences presented in electrical characteristics and mechanical performance when the negative pulse voltage is superimposed on the peak of AC signal.The strong pulse discharge is produced in the falling edge of voltage and the instantaneous plasma extension with the streamer discharge channels is formed.Then,a temporarily intensified local electric field enhances the streamer discharge and decreases time-average surface potential in the further downstream area,which results in the decreasing spatial airflow velocity,thrust and efficiency.The systematic study has shown that the enhanced glow-like discharge and increased surface potential in the further downstream area caused by the pulse-induced breakdown in the rising edge can improve the mechanical performance of SDBD plasma actuator.Nevertheless,the enhanced streamer discharge and decreased surface potential in the further downstream area caused by the pulse-induced breakdown in the falling rising edge limit the mechanical performance of SDBD plasma actuator.