| Atmospheric dielectric barrier discharge(DBD)has attracted much attention in military and industrial applications since it requires simple work environment,electrode arrangements or power supply parameters,and is easy to realize large-scale applications.To enhance efficiency and expand application range,the improvements of atmospheric air discharge intensity,stability and uniformity have drawn the great attention of researchers.Among them,discharge uniformity has always been the focus of many researchers.At present,the uniform discharges have been achieved in atmospheric helium or nitrogen discharge,and it has been confirmed that the gas flow will facilitate the generation of uniform discharge.It is generally difficult to obtain a uniform discharge in an atmospheric air discharge,while the application of airflow is also advantageous for the improvement of discharge uniformity.In the meanwhile,the airflow is unavoidable in many applications of atmospheric air discharges,and the presence of airflow strongly affects the discharge characteristics.Therefore,it is of great practical significance to clarify the action mechanism of airflow on air discharge,and it also contributes to deepening the understanding of the discharge plasma characteristics,which has high scientific value.In this thesis,the plate-to-plate DBD and pin-to-plate DBD are generated by AC power or nanosecond pulse power in atmospheric air.To study the airflow effect on the atmospheric DBD,the following reaches have been carried out:1.The effects of airflow on the characteristics of the atmospheric air DBD are investigated using the plate-to-plate DBD reactor excited by an AC power.The electrical characteristics,the optical emission spectrum(OES)are measured and the discharge images are taken with different exposure time at the airflow rate of 0-40 m/s.Experiment results show that the breakdown voltage decreases and more current pulses with declined amplitudes are produced when the airflow is introduced into the discharge gap.The gas temperature and the electron temperature,which are obtained from the OES,are declined with the increase in the airflow rate.The electron density remains unchanged.It is confirmed that the discharge mode remains a filamentary one in airflow,but different discharge states are observed.A stripe distribution is observed when the airflow rate is lower than 10 m/s and a cotton-like distribution is observed when the airflow rate exceeds 10 m/s.When the discharge has a stripe distribution,it can be recognized that the discharge filaments move along the airflow field direction with a velocity less than the corresponding airflow rate.When the discharge has a cotton-like distribution,the discharge filaments jitter during different discharge cycles and the directional movement is not observed.The observed phenomena are explained by the airflow effect on the charges during discharge decay phase.Owing to a lower breakdown voltage,more discharge filaments are generated.And the positions of discharge filaments change between different cycles,which attributes to the weakened memory effect caused by airflow.The overall effect of airflow is the discharge uniformity is improved.2.Experimental investigations of the breakdown characteristics of plate-to-plate DBD excited by an AC source at different gas flow conditions are carried out by using different discharge gases(including indoor air and dry air,N2,O2).The initial breakdown voltage for the appearance of the very first discharge filament and the breakdown voltage for the current occurrence in each discharge half cycle in continuous operation are examined.With the increase in the gas flow rate,the initial breakdown voltage of the indoor air discharge manifests a monotonous increase.While the breakdown voltage has a marked decline at the low gas flow rate,then increases slightly and remains unchanged as the gas flow rate is higher than 10 m/s.The experiments are also carried out in other dry gases.The results show that the initial breakdown voltages are unchanged,and the breakdown voltages increase at first and remain unchanged when the gas flow rate is higher than 10 m/s in dry air/N2.The gas humidity,temperature and the concentration of metastable particles are measured.As regards the obvious decreases in the initial breakdown voltage and breakdown voltage,the decrease in the humidity with the increase in the gas flow rate plays a dominant role.As regards the increase in breakdown voltage,the losses of metastable particles,together with heat in the gas flow,are considered to be the most critical factors.3.The effects of airflow on DBD characteristics are investigated by pin-to-plate DBD arrangements with an AC exciting source,the discharge characteristics under the airflow of 0-50 m/s are investigated by electrical measurement and time-resolved discharge image capture.The single-pin electrode is used to investigate the airflow effect on the discharge channel movement,and the double-pin electrode is used to investigate the airflow effect on the discharge channel interaction.The experiment results of single-pin discharge show that,the current intensities of "glow-like" discharge in positive cycles increase and the current intensities of "streamer" discharge in negative cycles decrease by airflow.The discharge channels move with the airflow with a movement velocity less than the corresponding airflow rate.The transition from a filamentary discharge to a diffuse discharge is observed at lower airflow rate when the airflow position is higher.In the cases of double pin electrode arrangements,the repulsion between double pin discharge channels is apparent at a 10 mm distance but is not obvious at a 20 mm distance.When the airflow is introduced into the discharge gap,the movements of discharge channels in airflow are affected by adjacent discharge channels especially when the repulsion effect is apparent.For the discharge channel in upstream,the electrostatic repulsive force and the airflow drag force are in opposite directions,the discharge channel could bend to the downstream only if the airflow drag force exceeds the electrostatic repulsive force.For the discharge channel in downstream,the electrostatic repulsive force and the airflow drag force are in the same direction,the discharge channel has a large range of movement to the downstream part.4.The generation and the evolution of diffuse nanosecond DBD in high-speed(0-280 m/s)airflow are investigated.The long-exposure discharge images and the high-speed camera images of continuous discharge cycle are captured,the photocurrent signals of different discharge areas are measured.On the introduction of airflow to the gas gap,two new discharge states are observed:diffuse discharge(DD)and thin filament discharge(TFD).At low airflow rate,the whole discharge space manifests DD.When the airflow rate is higher,the TFD appears in the upstream region and the DD remains in the downstream region.The length of TFD region is larger when the airflow rate is higher,the pulse repetition frequency is lower,or the applied voltage is lower.The length of TFD region is larger than the electrode length and the whole discharge space manifests TFD at the airflow rate higher than 110 m/s.It is observed from the high-speed camera images that the DD and the TFD are ignited at the upstream electrode boundary,subsequently move towards the downstream region with the airflow.Subsequent to hundreds of pulse cycles,a stationary distribution of discharge state is formed.The evolution velocities of DD and TFD are far less than the airflow rate or the movement velocity of discharge filaments.The observations presented above are ascribed to the redistribution of charges under the transverse electric field at the electrode boundary and the action of airflow.The nanosecond discharge mode is changed by the airflow and the discharge uniformity is promoted,and it is of great significance for the applications. 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