Probe Measurements of Parameters of Streamers of Nanosecond Frequency Crown Discharge

Investigations of the parameters of single streamers of nanosecond frequency corona discharge, creating a voluminous low-temperature plasma in extended coaxial electrode systems, are performed. Measurements of the parameters of streamers were made by an isolated probe situated on the outer grounded electrode. Streamers were generated under the action of voltage pulses with a front of 50–300 ns, duration of 100–600 ns, and amplitude up to 100 kV at the frequency of 50–1000 Hz. The pulse voltage, the total current of the corona, current per probe, and glow in the discharge gap were recorded in the experiments. It was established that, at these parameters of pulse voltage, streamers propagate at an average strength of the electric field of 4–10 kV/cm. Increasing the pulse amplitude leads to an increase in the number of streamers hitting the probe, an increase in the average charge of the head of a streamer, and, as a consequence, an increase in the total streamer current and the energy introduced into the gas. In the intervals up to 3 cm, streamer breakdown at an average field strength of 5–10 kV/cm is possible. In longer intervals, during the buildup of voltage after generation of the main pulse, RF breakdown is observed at Е_av ≈ 4 kV/cm.     

Active plasma grid for on-demand airflow mixing increase

The present paper concerns the electromechanical characterization of an actuator composed of a ceramic plate perforated by 121 holes housing embedded and printed electrodes between which a high voltage is applied. The electrode arrangement is such that the holes where the gas flows are surrounded by surface discharges. Electrical measurements and iCCD images show that the discharge behaves as a typical surface dielectric barrier discharge with streamer and glow regimes during one period of the AC sine voltage. Particle image velocimetry has been used to measure the jet flow produced by the discharge. The plasma discharge is at the origin of a wall jet with mean velocity of about 2.2 m/s, oriented from the active electrode to the grounded one. The capability of this discharge for promoting mixing by reducing the length of the jet core is demonstrated for flow velocities from 20 up to 60 m/s. In all the tested cases, the actuator can improve the mixing downstream of the perforated plate, when periodic perturbations are imposed at the jet column mode (St_D = 0.3).     

Positive discharge from a grounded electrode toward negatively charged particles cloud

In order to understand electrostatic discharges occurring between a grounded electrode and a space charge cloud, the positive discharges were experimentally caused by negatively charged particles cloud. The discharges were initiated by locating a grounded sphere electrode at the inside or outside of the charged powder particles blown by an air flow. The luminous aspect and the discharge current were observed for the grounded sphere electrode with various diameters. Positive streamer corona discharges extended from it. The luminous aspect, peak value of the discharge current and the interval of the discharge significantly depend on the diameter of the grounded sphere electrode as well as its position.     

等离子体激励翼型分离流动控制数值模拟

文章利用CFD软件FLUENT中的自定义函数接口, 将等离子体对中性气体的激励作用模型化为体积力引入Navier-Stokes方程, 研究了等离子体气动激励诱导的平板射流, 以及介质阻挡放电(dielectric barrier discharge, DBD)等离子体激励对NACA0015翼型大迎角分离流的控制作用.计算分析表明, 多对电极等离子体激励器可以有效控制NACA0015翼型大迎角分离流动.      

大气压氩气介质阻挡辉光放电的一维仿真研究

为了研究氩气(Ar)中介质阻挡大气压辉光放电(APGD)的放电机理, 通过建立一个一维的多粒子自洽耦合流体模型, 采用有限元方法进行数值计算, 得到了气体间隙压降、介质表面电荷密度、放电电流密度随时间的周期变化波形, 以及电子、离子、亚稳态粒子密度和空间电场强度的时空分布. 仿真计算结果表明：介质表面积聚的电荷对于放电的过程的起始及熄灭具有重要作用;当增大外施电压时, 放电击穿时刻提前, 放电电流密度和介质表面电荷密度峰值增大, 表明放电过程更加剧烈;随着阻挡介质相对介电常数的增大, 放电电流密度也随之增大. 各粒子密度及电场的时空分布表明放电过程在外施电压半个周期中只有一次放电, 且存在明显的阴极位降区、负辉区、等离子体正柱区等辉光放电的典型区域, 为大气压辉光放电(APGD).     

Resonance Properties of a Low-Pressure Dielectric Barrier Discharge

Technical Physics - The electrical characteristics of a dielectric barrier discharge (DBD) symmetrical actuator at low pressures gave been investigated. A power source–actuator–DBD...     

Enhancement of thin air jets produced by ring-shaped dielectric barrier discharges using an auxiliary electrode

A ring-shaped dielectric barrier discharge (DBD) was explored as a small form factor ionic wind device. Using a concentric ring electrode geometry, the DBD produced a converging ionic wind that leads to a vertical flow away from the DBD electrodes. The vertical flow was channeled through an outlet nozzle to produce a thin air jet, and a grounded auxiliary electrode was placed at the nozzle to enhance the exit velocity. The inner diameter of the ring-shaped DBD electrode and the auxiliary electrode ranged 3.18–9.54 mm and 1.0–4.0 mm, respectively. Results showed that the auxiliary electrode generated an ionic wind velocity up to 3.7 m/s and increased the conversion efficiency from discharge to flow power by a factor of 30 by strengthening the electric field where the ions are accelerated.     

Influence of wire mesh electrodes on the volume and surface characteristics of dielectric barrier discharge of atmospheric pressure helium

The dielectric barrier discharge of helium in a 6 mm gap at atmospheric pressure was studied. In this paper, the influence of electric field distribution on the uniformity of DBD is analyzed theoretically and verified by experiments. The experimental results show that the mesh electrode produces a local enhancement effect by affecting the electric field and then produces corona discharge, which provides seed electrons for the subsequent discharge process. The effects of mesh diameter and size on discharge uniformity and stability are analyzed, the electrode structure parameters are optimized, the method of a segmented electrode is proposed, and the discharge process and charge distribution are studied. The electrical diagnosis results of plasma technology show that the segmented mesh electrode reduces the breakdown voltage of DBD and increases the charge deposition.     

纳秒脉冲表面介质阻挡放电特性实验研究

在常规大气环境条件下,基于单极性纳秒脉冲电源对表面介质阻挡放电特性进行了实验研究。结果表明:纳秒脉冲表面介质阻挡放电的本质是丝状放电,放电集中在电压脉冲的上升沿;激励电压和脉冲重复频率越大,放电越强烈,越接近均匀放电,但电压的作用更侧重于均匀性,而频率的作用则侧重于放电的强度;电极间隙的优化可以使表面介质阻挡放电特性最好;玻璃作为阻挡介质时容易发生沿面闪络。     

Highly time-resolved investigation of the electric wind caused by surface DBD at various ac frequencies

Surface plasma discharges find relevant applications for manipulating laminar or turbulent flows. The control mechanism can be related to time-averaged momentum transfer or be associated to favorable interactions between the fluctuations imposed by the discharge and the natural instabilities developing in the incoming flow. In the present paper, the electric wind produced by a non-thermal surface dielectric barrier discharge is investigated by a non-intrusive measurement technique having a high temporal resolution. The measurements are carried out for an actuator in quiescent flow condition, but also for an actuator placed in the test section of a wind tunnel with external flow speed from 5 to 30 m/s. The results confirm that a surface DBD actuator has a low control authority on the mean characteristics of the velocity profiles developing above the plasma region. However, it is also demonstrated that the plasma actuator imposes periodic fluctuations at the electrical frequency driving the gas ionization, this over the whole range of tested speeds.     

Discharge and flow characterizations of the double-side sliding discharge plasma actuator

We investigate the discharge and flow characterizations of a double-side siding discharge plasma actuator driven by different polarities of direct current(DC) voltage. The discharge tests show that sliding discharge and extended discharge are filamentary discharge. The irregular current pulse of sliding discharge fluctuates obviously in the first half cycle,ultimately expands the discharge channel. The instantaneous power and average power consumptions of sliding discharge are larger than those of the extended discharge and dielectric barrier discharge(DBD). The flow characteristics measured by a high-frequency particle-image-velocimetry system together with high-speed schlieren technology show that the opposite jet at the bias DC electrode is induced by sliding discharge, which causes a bulge structure in the discharge channel.The bias DC electrode can deflect the direction of the induced jet, then modifying the properties of the boundary layer.Extended discharge can accelerate the velocity of the starting vortex, improving the horizontal velocity profile by 203%.The momentum growth caused by extended discharge has the largest peak value and the fastest growth rate, compared with sliding discharge and DBD. However, the momentum growth of sliding discharge lasts longer in the whole pulsed cycle,indicating that sliding discharge can also inject more momentum.     

Neutralization of charged dielectric materials using a dielectric barrier discharge

Safety and efficiency are two characteristics that must be satisfied by an electric charge neutralizer. The dielectric barrier discharge (DBD), which has the advantage of preventing arc transition, is an interesting tool to safely neutralize unwanted charge. This paper is aimed at studying the efficiency of neutralizing charged polyethylene (PE) granules by using a dielectric barrier discharge. During this study, several factors were considered such as the amplitude and the frequency of the AC voltage, the polarity and the charging mode of the samples, as well as the electrode configuration. Two DBD electrode configurations were considered: simple DBD and a DBD with installed metallic grid. The obtained results show that using the DBD can lead to excellent neutralization results when the grid is installed. With the appropriate voltage amplitude and frequency and with grid installed, the elimination of nearly 99% of the initial surface charges can be achieved. The metallic grid placed between the DBD electrode and the target enhances significantly the neutralization efficiency.     

��������������������������������ܵķ����о�

基于介质阻挡放电等离子体体积力气动激励机理,数值研究了两种等离子体流动控制方案对螺旋桨桨径根部处于负攻角工况下叶素气动性能的改善效果.结果显示,激励器布置在下翼面时等离子体体积力大于其布置在叶素前后缘时的情况;激励器布置在下翼面时,可抑制流动分离,使得螺旋桨桨根部位叶素产生更大的负拉力,但会减小螺旋桨的扭矩;激励器布置在前后缘时,会使螺旋桨根部叶素拉力增大,提高螺旋桨总拉力,但不能抑制流动分离,所以会增大螺旋桨的扭矩.     

Comparison between AlN and Al_2O_3 ceramics applied to barrier dielectric of plasma actuator

This paper reports the material characterization and performance evaluation of an AlN ceramic based dielectric barrier discharge(DBD) plasma actuator. A conventional Al_2O_3 ceramic is also investigated as a control. The plasma images,thermal characteristics and electrical properties of the two actuators are compared and studied. Then, with the same electrical operating parameters(12-kV applied voltage and 11-kHz power frequency), variations of the surface morphologies,consumed power and induced velocities are recorded and analyzed. The experimental results show that the AlN actuator can produce a more uniform discharge while the discharge of the Al_2O_3 actuator is easier to become filamentary. The later condition leads to higher power consumption and earlier failure due to electrode oxidation. In the plasma process,the power increment of the AlN actuator is higher than that of the Al_2O_3 actuator. The induced velocity is also influenced by this process. Prior to aging, the maximum induced velocity of the AlN actuator is 4.2 m/s, which is about 40% higher than that of the Al_2O_3 actuator. After 120-min plasma aging, the maximum velocity of the aged AlN actuator decreases by 27.8% while the Al_2O_3 actuator registers a decrease of 25%.     

脉冲放电产生螺旋流注的等离子体特性研究

通过脉冲放电方式产生三维螺旋形的等离子体放电通道,在高速摄像机拍摄下观察到放电通道中的发光电离体以流注形式沿螺旋轨迹快速传播.建立电磁模型解释螺旋放电的形成机制,对造成对称性破缺及影响其手性性质的极向电场进行分析.研究表明,螺旋放电产生的放电通道存在两种不同的手性特征,而脉冲重复频率等放电参数及边界条件对螺旋流注的传播特性存在影响.脉冲电源驱动的电磁场在介质管内所形成的波模是极向电场形成的一个重要来源,当极向电场与轴向电场强度相近时则形成螺旋流注放电.     

Time-resolved processes in a pulsed electrical discharge in argon bubbles in water

A phenomenological picture of a pulsed electrical discharge in gas bubbles in water is produced by combining electrical, spectroscopic, and imaging characterization methods. The discharge is generated by applying 1 m\mu s pulses of 5 to 20 kV between a needle and a disk electrode submerged in water. An Ar gas bubble surrounds the tip of the needle electrode. Imaging, electrical characteristics, and time-resolved optical emission spectroscopic data suggest a fast streamer propagation mechanism and the formation of a plasma channel in the bubble. Comparing the electrical and imaging data for consecutive pulses applied to the bubble at a frequency of 1 Hz indicates that each discharge proceeds as an entirely new process with no memory of the previous discharge aside from the presence of long-lived chemical species, such as ozone and oxygen. Imaging and electrical data show the presence of two discharge events during each applied voltage pulse, a forward discharge near the beginning of the applied pulse depositing charge on the surface of the bubble and a reverse discharge removing the accumulated charge from the water/gas interface when the applied voltage is turned off. The pd value of ~ 300–500 torr cm, the 1 μs long pulse duration, low repetition rate, and unidirectional character of the applied voltage pulses make the discharge process here unique compared to the traditional corona or dielectric barrier discharges.     

常压窄间隙介质阻挡放电等离子体辐射特性

利用带有透明电极与可测向观察的一个介质阻挡放电(DBD)实验装置对它的常压窄间隙等离子体辐射特性进行了实验研究。结果表明：这一DBD装置的辐射特性会受激励电压、激励频率、DBD结构等多种因素影响。在频率为10～20kHz高压电源激励下,采用窄间隙、薄电介质层结构DBD可以大幅度提高放电空间的电场强度,增加放电功率密度,提高了放电装置性能。     

Investigation of a single dielectric barrier discharge in submillimeter air gaps: Uniform field

The characteristics of a single discharge in 0.01–0.2-cm air gaps are investigated under atmospheric pressure between the metal electrodes and in the presence of a polymer barrier on one of the electrodes. The experimentally determined surface charge density distributions are satisfactorily described by a 2D Gaussian function with the proposed parameters. In the uniform field, the breakdown voltage weakly depends on the presence of a dielectric barrier. At the same time, the change from the positive to negative polarity of the metal electrode leads to a manifold increase in the discharge current and in the surface charge. The breakdown occurs under considerable overvoltage; the estimates indicate the streamer mechanism of the breakdown.     

Uniformity analysis of dielectric barrier discharge (DBD) processed polyethylene terephthalate (PET) surface

A dielectric barrier discharge (DBD) plasma, operating in air at atmospheric pressure, has been used to induce changes in the surface properties of polyethylene terephthalate (PET) films. The effects that the key DBD operating parameters: discharge power, processing speed, processing duration, and electrode configurations, have on producing wettability changes in the PET surface region have been investigated. The approach taken involves the application of an Taguchi experimental design and robust analysis methodology. The various data sets obtained from these analyses have been used to studies the effect of the operating parameters on the surface uniformity and efficiency of the said treatment.In general, the results obtained indicate that DBD plasma processing is an effective method for the controlled surface modification of PET. Relatively short exposures to the atmospheric pressure discharge produces significant wettability changes at the polymer film surface, as indicted by pronounced reductions in the water contact angle measured. It was observed that the wettability of the resultant surface shows no significant differences in respect to orientation parallel (L-direction) or perpendicular (T-direction) to the electrode long axis. However, there was significant differences between the data obtained from these two orientations. Analysis of the role of each of the operating parameters concerned shows that they have a selective effectiveness with respect to resultant surface modification in terms of uniformity of modification and wettability. The number of treatment cycles and the electrode configuration used were found to have the most significant effects on the homogeneity of the resultant PET surface changes in L- and T-orientation, respectively. On the other hand, the applied power showed no significant role in this regard. The number of treatment cycles was found to be the dominant factor (at significance level of 0.05) in respect of water contact angle changes at the processed PET surface in both orientations. The driven metal electrodes (stainless steel or aluminium) were apparently superior to the driven dielectric electrode (ceramic or quartz) configurations. The grounded electrode in each case was a silicon rubber-covered aluminium plate (see later). The nature and scale of the surface changes that originate from the various processing conditions employed have been considered so as to determine the optimum treatment conditions in respect of processing outcomes, properties and any orientation dependence. Thus, it was revealed that higher processing speeds and longer processing durations are key for uniformity along the electrode axial orientation, while lower processing speeds and short exposure durations are key considerations, in the corresponding perpendicular orientation. In general, longer processing durations (low processing speeds and a high number of treatment cycles) and higher plasma powers induced greater changes in the surface wettability of the PET, as demonstrated by the observed water contact angles. This behaviour is taken to indicate that different combinations of DBD operating parameters and electrodes produce discharge conditions that can result in different plasma chemical processes in respect of uniformity, treatment efficiency and orientation dependence.     

Ionic wind produced by an electro-aerodynamic pump based on corona and dielectric barrier discharges

The present study aims at showing the ability of ac discharges to be used as fanless blower in a rectangular channel. First, a 10 mm-high channel is used with four different types of ac atmospheric air discharges: an ac wire-to-plate corona discharge, two different ac wire-to-plate dielectric barrier discharges (DBD) and a surface DBD. The electrical and mechanical characteristics of the four different discharges are investigated and compared. They highlight that the best geometrical configuration is the wire-to-plate DBD with a thick dielectric, that allowed us to induce ionic wind velocity up to 3.3 m/s and flow rate per unit spanwise length of 24 L per second per meter. Secondly, this optimized configuration is reduced in size (2 mm-high channel) and the effect of this downscaling on the plasma actuator performances is studied, showing that the efficiency decreases with the channel height.