三电极共面介质阻挡放电的放电特性及诱导气流实验研究

等离子体流动控制激励器由于其响应速度快、激励频带宽、能量损耗低、可靠性强的优势,在航空航天领域的主动流动控制等方面得到了广泛应用.文章提出了一种新型的等离子体气动激励器——三电极共面介质阻挡放电激励器,研究了该激励器电极结构对放电特性和诱导气流速度的影响,并与传统共面介质阻挡放电和沿面介质阻挡放电激励器进行了比较.结果表明:（1）随着激励电压的提高,高压电极和地电极之间先出现了丝状放电并逐渐延伸到第三电极;（2）随着第三电极与高压电极之间的距离增大,诱导气流速率从2.4 m/s下降到0 m/s,而第三电极宽度的变动对诱导气流速度影响可忽略不计;（3）相同外部条件下,该激励器诱导的气流速度小于沿面介质阻挡放电激励器,但高于共面介质阻挡放电激励器.      

Electrical and optical characteristics of the radio frequency surface dielectric barrier discharge plasma actuation

Electrical characteristics and optical emission spectrum of the radio frequency(RF) surface dielectric barrier discharge(SDBD) plasma actuation are investigated experimentally in this paper. Influences of operating pressure, duty cycle and load power on the discharge are analyzed. When the operating pressure reaches 30 kPa, the discharge energy calculated from the Charge–Voltage(Q–V) Lissajous figure increases significantly, while the effective capacitance decreases remarkably. As the duty cycle of the applied voltage increases, the voltage–current waveforms, the area of Q–V loop and the capacity show no distinct changes. Below 40 W, effective capacitance increases with the increase of load power, but it almost remains unchanged when load power is between 40 W and 95 W. The relative intensity I_(391.4)~peak/I_(380.5)~peak changes little as the operating pressure varies from 4 kPa to 100 kPa, while it rises evidently with the pressure below 4 kPa, which indicates that the RF discharge mode shifts from filamentary discharge to glow discharge at around 4 kPa. With the increase of load power, the relative intensity I_(391.4)~peak/I_(380.5)~peak rises evidently. Additionally, the relative intensity I_(371.1)~peak/I_(380.5)~peak is insensitive to the pressure,the duty cycle, and the load power.     

亚微秒脉冲表面介质阻挡放电等离子体诱导连续漩涡的研究

使用粒子激光图像测速技术对亚微秒脉冲激励表面介质阻挡放电激励器连续产生诱导漩涡进行了实验研究, 给出了包含脉冲重复频率和漩涡频率的双频率激励模式的具体形式. 实验过程中出现了原发型与继发型两类示踪粒子空白区, 前者由放电释热的微爆炸作用造成, 使得诱导流动远离壁面, 能够减小壁面摩擦阻力的作用; 以暴露电极左侧继发型空白区被完全吹除作为重复启动激励的临界点. 为提高控制效果应采用尽可能高的脉冲重复频率, 漩涡时间内脉冲数量应大于10, 最大诱导速度随脉冲数量增大而增大, 但动量传递效率降低. 使用亚微秒脉冲激励具备释热、体积力两种作用机理. 关键词： 双频率亚微秒脉冲 表面介质阻挡放电 连续漩涡     

激励电压对沿面介质阻挡放电特性的影响分析

近年来, 沿面介质阻挡放电(SDBD) 用作大气压下气流控制的等离子体激励器因其众多的优点受到了广泛的关注. 然而, 国内外对沿面介质阻挡放电及其应用的研究尚处于探索阶段, 对其放电特性的影响因素缺乏规律性的认识. 因此, 对SDBD 相关特性和影响因素进行研究具有重要理论意义和应用价值. 本文使用频率5 ~20 kHz,峰值电压0~30 kV 的可调正弦交流电源激励大气压环境下的 SDBD 装置. 通过调节激励电压大小, 研究了其与SDBD 放电特性之间的关系, 对等离子体放电电流、 放电形貌、 功率损耗、 诱导气流以及机械效率进行了分析. 实验结果表明,SDBD 消耗功率、 放电强度和诱导气流均会随着激励电压的增大而增大, 但机械效率存在先增大后减小的趋势, 说明等离子体流动控制中研究中存在最佳效率点.     

Cathode-sheath driven low-speed aerodynamic flow actuation using direct-current surface glow discharges

Flow actuation by a continuous/pulsed, direct-current (DC) surface glow discharge is explored. The discharge comprises an array of pin electrode pairs flush mounted on a dielectric actuator surface that lies adjacent to stagnant air. Strong electrostatic fields produced in the cathode sheath region of the discharge provides a motive force on the ions which in turn drag the background gas resulting in directed air flow from the anode to the cathode. The induced flow velocity is estimated by particle image velocimetry (PIV) at 10 Hz with TiO₂ seeding. For a pulsed DC discharge with peak power of 5 W per electrode pair, the induced flow velocity reaches peak values of about 1.7 m/s which is comparable to dielectric-barrier discharge (DBD) or corona discharge actuators. The actuation effect quantified by the magnitude of induced velocity increases as the pulse frequency increases from 0 to 1 kHz. The actuation effect decreases for further increase in frequency above 1 kHz. Decreased actuation effect at high frequency is accompanied by structural change in the discharge. At fixed frequency of 1 kHz, flow actuation effect is highest for a square wave pulse with a duty cycle of 50% indicating that pulsed DC discharges produces better actuation than continuous DC with a corresponding reduction in energy consumption.     

光谱方法研究大气压氩气等离子体喷枪的放电特性

利用同轴介质阻挡放电喷枪,通过氩气的流动在大气压空气中产生了均匀的等离子体羽。等离子体羽沿气流方向较为均匀,但在喷嘴处为白色且亮度较高,远离喷嘴处为蓝色,亮度较低。研究了等离子体羽长度与外加电压幅值、驱动频率和气体流速的关系,气流小于4 L·min-1时等离子羽的长度随气流的增大而增大,而当气流大于4 L·min-1时长度随气流的增大而减小。当气流保持恒定时,等离子体羽的长度随外加电压幅值或驱动频率的增大而增大。结合气体放电理论以及分析湍流和平流对放电的影响,对等离子体羽长度随实验参数的变化进行了定性解释。光学方法研究发现在外加电压正半周期等离子羽有一个发光脉冲,而负半周期没有发光信号。同轴介质阻挡放电正半周期有两个发光脉冲,负半周期有一个发光脉冲。通过对该N₂现象的分析,为等离子体羽的产生机制提供了一种可能的解释。采集了同轴介质阻挡放电和等离子体羽的发射光谱,研究发现除等离子体羽存在明显的OH和N₂的发射谱线外,其发射光谱没有明显差别。利用光学发射谱N+₂第一负带系,对等离子体羽转动温度进行了测量,发现转动温度沿远离喷嘴的方向逐渐降低,且转动温度随电压幅值的增大而增大。     

感应式脉冲推力器中等离子体加速数值研究

为了分析感应式脉冲放电等离子体推力器中时变电磁场作用下等离子体的放电参数分布及其随着磁场强度变化的影响,引入了利用双曲型散度清除方法的二维轴对称瞬态等离子体流动的磁流体力学数值模型.计算结果表明,随着输入能量的增加,等离子体团出现速度峰值的时刻提前,等离子体中同时存在的异号电流环对其加速具有阻滞作用.等离子体的加速效率随着磁场强度非线性增大,磁场大于某一临界值时(几何构型下峰值磁场强度大于0.45 T),有限空间情况下等离子体的加速效率获得显著提高.     

纳秒激光诱导空气等离子体射频辐射特性研究

开展了波长为532 nm、脉宽为8 ns的纳秒激光诱导空气等离子体射频电磁辐射特性实验研究,基于锥形天线探测空气等离子体在30-800 MHz频谱范围有较强的射频电磁辐射,是等离子体内电偶极子振荡变速运动造成的.实验结果表明:随激光能量增加,30-200 MHz范围内射频辐射强度逐渐变强,但360-600 MHz频率范围射频辐射强度逐渐变弱.等离子体射频辐射的空间分布依赖于入射激光的偏振方向,当激光偏振方向与天线放置方向一致时,该方向上空气等离子体的射频辐射强度高,谱线较丰富.射频辐射总功率随激光能量先增加后降低,采用等离子体电子密度变化对等离子体频率及等离子体衰减系数影响(制约)关系,对射频辐射总功率随激光能量的变化规律进行了解释.     

等离子体处理的聚丙烯和聚乙烯的粘合体

采用射频辉光放电等离子体和介质阻挡放电等离子体对聚丙烯（PP）和聚乙烯（PE）进行处理后,使用聚氨酯进行粘接,并测试了混合粘合体的剪切强度。介质阻挡放电功率是100 W时,等离子体处理对混合粘合体的剪切强度无影响。介质阻挡放电的功率为200 W、处理时间20 s时,等离子体处理效果最佳,剪切强度为1.58 MPa,是未处理的混合粘合体的14.36倍。介质阻挡放电的功率是300 W时,样品在10 s内就被击穿。射频辉光放电等离子体中,使用空气处理后最大剪切强度为1.60 MPa（100 W,3 min）,使用氮气处理后的最大剪切强度为1.57 MPa（200 W,3 min）。通过扫描电镜（SEM）对等离子体处理前后的PP表面形貌观察,发现未处理样品的表面比较平滑,而经等离子体放电处理后的样品表面变得疏松,出现了大量泡状物质,表面粗糙程度提高。     

13.56 MHz/2 MHz柱状感性耦合等离子体参数的对比研究

通过Langmuir双探针和发射光谱诊断方法,对比研究了驱动频率为13.56 MHz和2 MHz柱状感性耦合等离子体中电子密度和电子温度的径向分布规律.结果表明:在高频和低频放电中,输入功率的增加对等离子体参数产生了不同的影响,高频放电中主要提升了电子密度,低频放电中则主要提升了电子温度.固定气压为10 Pa,分别由高频和低频驱动时,电子密度的径向分布均为"凸型".而电子温度的分布差异比较明显,高频驱动时,电子温度在腔室中心较为平坦,在边缘略有上升;低频驱动时,电子温度随径向距离的增加而逐渐下降.为了进一步分析造成这种差异的原因,在相同放电条件下采集了氩等离子体的发射光谱图,利用分支比法计算了亚稳态粒子的数密度,发现电子温度的径向分布始终与亚稳态粒子的径向分布相反.继续升高气压到100 Pa,发现不论高频还是低频放电,电子密度的径向分布均从"凸型"转变为"马鞍形",较低气压时电子密度的均匀性有了一定的提升,但低频的均匀性更好.     

Aerodynamic actuation characteristics of radio-frequency discharge plasma and control of supersonic flow

In this paper, aerodynamic actuation characteristics of radio-frequency(RF) discharge plasma are studied and a method is proposed for shock wave control based on RF discharge. Under the static condition, a RF diffuse glow discharge can be observed; under the supersonic inflow, the plasma is blown downstream but remains continuous and stable.Time-resolved schlieren is used for flow field visualization. It is found that RF discharge not only leads to continuous energy deposition on the electrode surface but also induces a compression wave. Under the supersonic inflow condition, a weak oblique shock wave is induced by discharge. Experimental results of the shock wave control indicate that the applied actuation can disperse the bottom structure of the ramp-induced oblique shock wave, which is also observed in the extracted shock wave structure after image processing. More importantly, this control effect can be maintained steadily due to the continuous high-frequency(MHz) discharge. Finally, correlations for schlieren images and numerical simulations are employed to further explore the flow control mechanism. It is observed that the vortex in the boundary layer increases after the application of actuation, meaning that the boundary layer in the downstream of the actuation position is thickened. This is equivalent to covering a layer of low-density smooth wall around the compression corner and on the ramp surface, thereby weakening the compressibility at the compression corner. Our results demonstrate the ability of RF plasma aerodynamic actuation to control the supersonic airflow.     

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.     

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%.     

Experimental investigation of nanosecond discharge plasma aerodynamic actuation

In this paper we report on an experimental study of the characteristics of nanosecond pulsed discharge plasma aerodynamic actuation. The N 2 (C 3 Π u ) rotational and vibrational temperatures are around 430 K and 0.24 eV, respectively. The emission intensity ratio between the first negative system and the second positive system of N 2 , as a rough indicator of the temporally and spatially averaged electron energy, has a minor dependence on applied voltage amplitude. The induced flow direction is not parallel, but vertical to the dielectric layer surface, as shown by measurements of body force, velocity, and vorticity. Nanosecond discharge plasma aerodynamic actuation is effective in airfoil flow separation control at freestream speeds up to 100 m/s.     

沿面型介质阻挡放电喷枪的发光特性及气体温度研究

利用氩气作为工作气体,采用正弦电压驱动沿面型等离子体喷枪,在大气压空气环境中产生了均匀的等离子体羽。电学和光学测量结果表明,等离子体羽放电只存在于外加峰值电压的正半周期,并且正半周期的放电脉冲个数随气体流量的增加而增加。通过对正半周期不同位置的发光脉冲信号进行比较,发现等离子体羽均按子弹形式传播,其中每一个发光脉冲均对应一次等离子体子弹传播过程。通过对比放电电流和等离子体羽的发光信号,发现等离子体羽的发光脉冲滞后于放电电流脉冲,且该延迟时间基本服从正态分布。该延迟时间随着外加电压峰值及气体流量的增大而减小。利用光纤测温仪测量了等离子体羽的气体温度,发现气体温度随外加峰值电压的增大而升高,随工作气体流量的增大而降低。通过分析放电过程,对上述现象进行了定性解释。     

Characteristics of an atmospheric‐pressure radio frequency‐driven Ar/H2 plasma discharge with copper wire in tube

This paper investigates a plasma discharge driven by a 13.56 MHz radio frequency (RF) power supply at atmospheric pressure, in which a copper wire is inserted in the discharge tube for the deposition of Cu films. The results show that the jet plasma formation originates from the discharge between the copper wire and induction coil because of its electrostatic field. The axial distribution of the plasma parameters in the RF plasma jet, namely the gas temperature, excitation temperature, and electron number density, is determined by diatomic molecule OH fitting, Boltzmann slope, and H_β Stark broadening, respectively. The discharge current significantly declines when a small amount of hydrogen is added to the argon as the plasma‐forming gas, and the gas temperature of discharge plasma increases considerably.     

气压对于低气压双频容性耦合Ar/O2 等离子体放电特性影响的研究

 研究了气压对双射频氩氧混合等离子体电子温度和电子密度的影响。在13.56MHz低频功率和94.92MHz高频功率固定为60W和氩氧气体比为1:9的情况下，利用发射光谱法分析了气压不同时氩氧混合等离子体的放电光谱中的特征谱线的变化规律。使用一维质点网格法(PIC-MC)静电模型计算了电子温度和电子密度。结果表明：电子温度随着气压的增加先降低后升高，与实验结果趋势相吻合；电子密度随着气压的增加先增大后减小。     

大气压脉冲调制射频氩气放电等离子体特性的数值研究

基于等离子体流体理论,建立了大气压脉冲调制射频氩气放电的一维流体模型。通过数值模拟的方 法研究了放电参数(放电电极间距、射频频率)对氩等离子体特性的影响。研究结果表明：当电压固定时,随着电 极间距的增加,等离子体区逐渐增大,最大电子密度也增加,在 0.20cm 达到最大值后略有降低;放电电流密度 与输入功率密度随着电极间距的增加而增加;鞘层区电子温度随着电极间距的增加而降低;在脉冲开启前期,等 离子体区电子温度随着电极间距的增加而增加,但当脉冲开启后期,电极间距对等离子体区电子温度影响较小。 不同射频频率下最大电子密度随电极间隙的增加而减小,也具有一个最优值。      

The effect of modulated electric field on characteristic of SDBD-like plasma jet for surface modification

In this paper, the dynamics and flow behaviour of an atmospheric argon plasma jet was studied in the new nozzle structure similar to the surface dielectric barrier discharge (SDBD) using the Schlieren imaging method. The effect of plasma jet driven by repetitive high-voltage microsecond pulses with low-frequency sinusoidal bias was measured qualitatively in a single mirror Schlieren optical system. The enhancement of plasma jet length and cross-section of plasma jet with surface in this condition is due to highly turbulent flow of argon plasma jet in this structure. This study revealed the important role of SDBD structure and modulated electric field on the behaviour of plasma jet in a high diameter nozzle. In practice, this technique allows us to increase the jet length of the nozzle output to 5 cm and under these conditions, the diameter of the plasma jet cross-section is increased to 8 mm, without increasing the electrical power consumption. Eventually, the hydrophilicity of the surface is also measured by the contact angle of a water droplet that decreases from 78° to 8° after surface treatment, implying we were able to reach a super-hydrophilic surface with this plasma jet structure.     

60MHz电容耦合等离子体中电子能量分布函数特性研究

甚高频(频率大于30 MHz)耦合放电源由于能产生大面积高密度的等离子体而受到了人们的广泛关注. 采用电流、电压探针以及朗缪尔探针诊断技术对60MHz射频激发产生的容性耦合等离子体的放电特性及电子行为进行了研究. 实验结果表明,等离子体的等效电阻/电容随着射频输入功率的增加而减小/增加;等离子体中电子行为不仅依赖于射频输入功率,还与放电气压密切相关;放电气压的增加导致电子能量概率分布函数(EEPF)从双温Maxwellian分布向Druyvesteyn分布转变,而且转变气压远低于文献所报道的数值,这主要是由于在60MHz容性耦合等离子体中电子反弹共振加热效率大为降低. 关键词： 甚高频容性耦合等离子体 朗缪尔探针诊断 电子加热模式