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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.     

等离子体气动激励机理数值研究

基于介质阻挡与准直流电弧放电的物理过程, 分析了它们的气动激励机理, 建立了各自的气动激励模型, 并分别研究了它们对低速和超声速流动的激励效果. 结果显示: 介质挡板放电等离子体气动激励机理是改变了连续流体中的三种力, 即由牛顿内摩擦引起的剪切应力、由电动力学引起的体积力及由压力突变引起的冲击力, 其中基于电动力学的体积力效应占主导地位; 临近空间环境中体积力的作用效果更强, 诱导速度更大; 超声速来流下准直流电弧放电气动激励机理主要是等离子体的热阻塞效应, 本文所建立的爆炸丝传热模型可以用于仿真其控制激波的过程; 热电弧对于超声速来流而言就像一个具有一定斜坡角度的虚拟突起, 可用于高超声速飞行器前体激波的控制.     

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.     

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).     

The role of vibrational temperature variations in a pulsed dielectric barrier discharge plasma device

The use of dielectric barrier discharge (DBD) plasmas has become a practical way to carry out surface treatment where precise control of the plasma parameters, such as rotational and vibrational temperatures (T_rot and T_vib), is required. As the T_vib of an atmospheric pressure plasma jet appears to be the most important parameter related to the improvement of surface treatments, in this work, we analysed two methods to increase the values of T_vib in a DBD plasma jet device. One of the methods is to reduce the exit size (ø) of the DBD reactor, which results in an increase in the measured T_vib values, due to an increase in the pressure inside the reactor. The other method is to change the gas flow rate (GFR) used to produce the plasma jets. This leads to a T_vib reduction when the GFR is increased in the case of using helium or nitrogen as the working gas, but the opposite happens (an increase in the T_vib values) when argon is used, with different phenomena causing the variation of T_vib in each situation.     

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。     

Role of the volume and surface breakdown in a formation of microdischarges in a steady-state DBD

The results of an experimental study on a spatial-time behavior of microdischarges (MDs) in steady-state dielectric barrier discharge (DBD) are presented. MDs of DBD have a spatial “memory”, i.e. every subsequent MD appears exactly at the same place that was occupied by the preceding MD. In most cases each MD appears at its fixed place only once by every half-period (HP). Spatial “memory” is derived from slow recombination of plasma in the MDs channels for a period between two neighbor HPs. In steady-state DBD each plasma column was formed only one-time due to local avalanche-streamer breakdown in the very first (initial) gas gap breakdown under inception voltage U^*U^*. After that DBD is sustained under voltage lower than U^*U^*. For the plane-to-plane DBD having the restricted electrode area there is a critical voltage U ₁: DBD is in a steady-state if U > U ₁ but the DBD decays slowly at voltages below U ₁. The decay takes many HPs and occurs due to decreasing the number of MDs inside the gap because of their Brownian motion from central region to the outside of the discharge area. In steady-state DBD there is no correlation between an appearance of alone MD and phase of the applied voltage – each MD has a great scatter in its appearance at the HP. This scatter is attributed to the dispersion in a threshold voltage for local surface breakdowns around the MD base. So, in steady-state DBD the MD volume plasma is responsible for an existence of spatial “memory” (i.e. where the MD appears) but the surface charge distribution around MD is responsible for MD time dispersion (i.e. when the MD appears).     

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基于介质阻挡放电等离子体的体积力气动激励机理,仿真研究了等离子体增升减阻技术对沿螺旋桨桨径方向均匀分布的10个叶素气动特性的改善效果.采用叶素理论,对比分析了等离子体对螺旋桨整体气动性能的提高效果.主要结论有:桨尖和桨叶根部的叶素容易发生气动分离现象,其中根部叶素处于负攻角的工况中;采用介质阻挡放电等离子体流动控制技术可以完全抑制流动分离不太严重的桨叶中部区域的叶素气动分离,对桨尖处翼型的严重气动分离不能完全抑制但也有改善作用,但对处于负攻角工况的叶素作用不大;等离子体增升减阻技术确实可以提高螺旋桨的气动性能,对本文所研究的情况,螺旋桨的拉力和效率分别提高了28.27％和 12.3％.     

吸收光谱法测量大气压空气介质阻挡放电的臭氧浓度

臭氧作为一种强氧化剂和杀菌剂,在污染物降解,食品加工,杀菌消毒,医疗卫生等方面有着非常广泛的应用。大气压介质阻挡放电是一种极为高效的产生臭氧的方法,利用平行平板介质阻挡放电装置,采用交流高压激励,产生了大气压空气非平衡态等离子体。通过测量其电压和发光信号,发现在电压的正、负半周期均存在着许多随机的放电脉冲,并且其脉宽均在几十到几百纳秒之间,这表明其机制是流光放电。放电的光学发射谱包含氮分子的第二正带系(C 3Π-B 3Π)和第一正带系(B 3П-A 3П),氮分子离子的第一负带系(B 2Σ-X 2Σ),以及氧原子谱线(715.7和799.5 nm)。由于流光放电在紫外区域(200~300 nm)没有明显的发射谱线,但臭氧在此区域存在吸收峰,因此可以利用此区域的紫外吸收光谱测量放电产生的臭氧浓度。吸收光谱法可以有效的监测其臭氧浓度的变化情况,其优势在于操作简单,对实验环境要求低,可在放电条件下使用,并且可以连续监测臭氧浓度变化。基于此,通过Beer-Lambert定律计算了臭氧浓度随实验参数的变化,结果发现随外加电压幅值和驱动频率的增加,臭氧浓度升高。这些结果对于大气压介质阻挡放电的工业应用具有重要价值。     

Statistical analysis of the effect of dielectric barrier discharge (DBD) operating parameters on the surface processing of poly(methylmethacrylate) film

A dielectric barrier discharge (DBD) plasma, operating in air at atmospheric pressure, has been used to induce changes in the surface properties of poly(methylmethacrylate) (PMMA) films. The relative effects that key DBD operating parameters, specifically: discharge power, electrode gap and duration of exposure have on producing chemical and microstructural changes in the polymer surface region have been investigated. The approach taken involves the application of an orthogonal array experimental design and statistical analysis methodology. The various data sets obtained from these analyses have been used to develop an equation in which induced changes in the surface properties of the DBD modified PMMA films are expressed in terms of the effectiveness of the various processing parameters in producing them.In general, the results obtained clearly indicate that DBD plasma processing is an effective method for the controlled surface modification of PMMA. Relatively short exposures to the atmospheric pressure discharge produces a significant amount of oxygen incorporation at the surface as indicted by a pronounced reduction in water contact angle. Analysis of the role of each of the operating parameters concerned shows that they do indeed have selective effectiveness for inducing resultant surface modification. Duration of exposure to the DBD plasma, expressed here as the number of treatment cycles at a given speed of specimen transit through the electrode gap, was found to play a major role in decreasing the surface wettability of PMMA. Conversely, the magnitude of the discharge power was not a significant parameter in this regard. In contrast, the value of the applied power played the dominant role in achieving the observed enrichment of the surface oxygen abundance, as measured by XPS, with the duration of exposure to the discharge playing a secondary role in this case.The nature and scale of the induced surface changes that originate from the various processing conditions employed have been further considered to determine if an interrelationship exists between them. Non-parametric data analysis indicates that no significant correlation exists between the observed changes in measured polymer wettability and the attendant surface oxygen enrichment. This result suggests that the increase in surface wettability caused by DBD processing, as manifested in a reduced contact angle, is not merely attributable to changes in the surface chemistry. As such, it is postulated that changes in the surface microstructure may also contribute to this change in surface wettability.     

Surface dielectric barrier discharge: Effect of encapsulation of the grounded electrode on the electromechanical characteristics of the plasma actuator

Active flow control is a rapidly developing topic because the associated industrial applications are of immense importance, particularly for aeronautics. Among all the flow control actuators, plasma-based devices are very promising. In most cases, the plasma actuator is based on a surface dielectric barrier discharge (DBD) established between two electrodes flush mounted on both sides of a dielectric layer. In this paper, the effects of the encapsulation of the grounded electrode on the electric wind produced by a surface DBD are investigated by Pitot velocity measurements. Moreover, the current versus time is statistically analysed in order to count the number of streamers, their duration and the electrical charge they transfer. Unfortunately it was not possible to detect and separate the glow-type synchronous current because its amplitude is of the same order as noise. On one hand, the encapsulation of the grounded electrode results in an increase of the electromechanical efficiency of the surface DBD plasma actuator because the electrical power consumption is divided by two. On the other hand, statistical analysis of the discharge current versus time has shown that the encapsulation results in a decrease of the streamer number and an increase of the charge transferred by each current streamer because the duration of streamers is longer.     

Surface cleaning effect of NCM powder and improvement of lithium ion battery on the thermal stability and life cycle employing dielectric barrier discharge technique

Mixed NCM (nikel, cobalt, and manganese) powder was treated by a reactive gas from dielectric barrier discharge (DBD) to prepare a cathode material in Lithium ion (Li-ion) battery. The DBD was mainly sustained using N₂ gas at atmospheric pressure, and NF₃, SF₆, and H₂ was fed into the discharge to create the reactive gas. Compare to the non-treated sample, impurities on the surface of the NCM powder were significantly removed in a 5 min when the reactive gas was blow into the powder and mixed properly. F atom content on the surface was increased depending on the time duration of mixing, which form a LiF layer on the surface. Desirable LiF layer suppress a heat flow effectively , resulting a decreasing of exothermic temperature inside the Li-ion battery. Additionally, the treatment of NCM powder employing DBD technique was also contributed to electrochemical performance, which was confirmed by c-rate testing.     

同轴介质阻挡放电发生器介质层等效电容和负载特性研究

大气压介质阻挡放电(DBD)可以在常压下产生非平衡等离子体,已经成为热点研究领域.通过脉冲或交变电源激发放电,研究电源输出特性、电源与放电发生器负载间的匹配和外界条件对放电的影响对于理解放电现象和提高放电效率具有重要意义.本文采用Lissajous图形法,分别研究了驱动电压、气流速率等因素影响同轴DBD发生器介质层等效电容及负载幅频特性的规律.结果表明,气流速率和驱动电压等外界条件影响DBD发生器的负载特性:介质层等效电容随气流速率增大而减小,随驱动电压增大而增大;幅频特性曲线均表现出RLC回路谐振现象,谐振频率随气流速率增大而增大,随驱动电压增大而减小.通过对比发现,介质层等效电容随频率的变化曲线与幅频特性曲线具有一致的特征,介质层等效电容是影响电路谐振频率动态变化的主要因素.提出了一种有关介质层等效电容的形成机制.     

Dynamic evolution of vortex structures induced by tri-electrode plasma actuator

Plasma flow control is a new type of active flow control approach based on plasma pneumatic actuation.Dielectric barrier discharge(DBD) actuators have become a focus of international aerodynamic research.However,the practical applications of typical DBDs are largely restricted due to their limited discharge area and low relative-induced velocity.The further improvement of performance will be beneficial for engineering applications.In this paper,high-speed schlieren and high-speed particle image velocimetry(PIV) are employed to study the flow field induced by three kinds of plasma actuations in a static atmosphere,and the differences in induced flow field structure among typical DBD,extended DBD(EX-DBD),and tri-electrode sliding discharge(TED) are compared.The analyzing of the dynamic evolution of the maximum horizontal velocity over time,the velocity profile at a fixed horizontal position,and the momentum and body force in a control volume reveals that the induced velocity peak value and profile velocity height of EX-DBD are higher than those of the other two types of actuation,suggesting that EX-DBD actuation has the strongest temporal aerodynamic effect among the three types of actuations.The TED actuation not only can enlarge the plasma extension but also has the longest duration in the entire pulsed period and the greatest influence on the height and width of the airflow near the wall surface.Thus,the TED actuation has the ability to continuously influencing a larger three-dimensional space above the surface of the nlasma actuator.     

米量级常压等离子体改性装置及其在纺织材料改性中的应用

介绍了自制的1m尺度介质阻挡电连续表面改性处理装置。论述了米量级常压介质阻挡放电的物理特性,探讨了介质阻挡放电的电压、功率、频率等电学参量之间的关系。给出了使用此装置连续对涤纶(PET)织物、熔喷PBT非织造布和羊毛织物三种纺织材料进行改性实验结果,得到了相应的扫描电子显微镜(SEM)图片,分析了材料表面改性的原因。     

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。     

Effective ozone generation utilizing a meshed-plate electrode in a dielectric-barrier discharge type ozone generator

A meshed-plate electrode, an alternative to the conventional plate electrode of the dielectric-barrier discharge (DBD) ozone generator, has been studied in order to show the effectiveness of the meshed-plate electrode in improving ozone generation. A DBD ozone generator with mesh electrode is shown to have the following two advantages: First, such a device produces corona at its thin, sharp edges, thereby decreasing corona onset voltage for a given gap spacing. Second, by utilizing the air-voids of the meshed-plate electrode, the dense ozone produced in the small, high temperature gap region of the DBD can escape rapidly to the low temperature region. As a result, decomposition of the ozone can be reduced. In this study, surface discharge, meshed-plate electrode, and conventional DBD ozone generators are studied and compared experimentally. The maximum ozone generation concentration and ozone generation efficiency are obtained with the meshed-plate type electrode.     

共面介质阻挡放电特性研究

对共面介质阻挡放电(DBD)的放电过程进行了实验和理论研究. 在实验中设计了分段电极方法来获取放电过程中不同位置上的局域电流和光辐射特性，得到了阴极上等离子体的扩展速度，并与二维流体数值模拟结果进行了比较. 结果表明，在共面DBD的暂态放电过程中，电极上空等离子体区域始终存在有不均匀电场，导致了不同位置上放电电流和光辐射分布的不一致. 同时研究还表明，在DBD放电过程中应当考虑表面光致二次电子发射. 关键词： 介质阻挡放电 分段电极 放电特性     

大气压氩气介质阻挡放电中的电子激发温度

采用发射光谱强度比法,测量了大气压氩气介质阻挡放电(DBD)中的电子激发温度。实验在690～800 nm的范围内测量了大气压氩气DBD的发射光谱,经分析发现这些谱线全部是氩原子的发射谱线。为了测量电子激发温度,选用相距较近的763.51 nm(2P₆→1S₅),772.42 nm(2P₂→1S₃)的两条光谱线。结果发现电子温度的范围为0.1～0.5 eV,电子激发温度随电压的增加而增加,随流量的增加而减小。实验还发现氩气流动与非流动时电子激发温度有明显的差别。上述结果对介质阻挡放电在工业领域上的应用具有重要意义。     

Formation of hydrophobic coating on PMMA surface using unipolar nanosecond-pulse DBD in atmospheric air

Dielectric barrier discharge (DBD) can modify the material surface and result in complicated physical and chemical reactions to improve the surface hydrophilicity, which is proved to be an effective method for surface modification. Compared with the traditional ac-excitation DBD, the DBD using unipolar pulses can avoid local overheat of microdischarges and can improve discharge efficiency under some conditions. In this paper, DBD excited by repetitive unipolar nanosecond generator was used to improve the hydrophobicity of Plexiglass (PMMA) surface by means of the interaction between air plasma and silicone oil. The output voltage had a rise time of 40 ns and a full width at half maximum of about 70 ns. The surface hydrophobicity of the PMMA, before and after the surface modification, was evaluated via the contact angle measurement under different experimental conditions. The values of the contact angle shown in this paper were the average of eight measured values, and the standard deviations were also calculated. The surface energy including polar and dispersion components was calculated using the measured average contact angles of distilled water and polyethyleneglycol. The results showed that, as the increase of the discharge voltage, the contact angle increased but the surface energy decreased. With the increase of treatment time, the water contact angle of the modified surface increased at the beginning, and it would reach to a maximum at 7.5 min treatment, and then decreased. The effect of pulse frequency on the modification results was different at various treatment times. In addition, the possible physical and chemical reaction among the DBD plasma, silicone oil and the PMMA surface was discussed.