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Experimental studies were conducted of a flow induced in an initially quiescent room air by a single asymmetric dielectric barrier discharge driven by voltage waveforms consisting of repetitive nanosecond high-voltage pulses superimposed on dc or alternating sinusoidal or square-wave bias voltage. To characterize the pulses and to optimize their ma...
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... is being heated and receives momentum in the downstream direction from left to right. The motion of the gas generates pressure gradient in the vicinity of interac- tion region. The gas is being sucked in that region from the left and from above, creating an upstream vorticity. At the same time another vortex is generated by the induced gas jet Fig. 8. There are important differences between the two vortices. One of them is the sign of vorticity. The vorticities of upstream and downstream vortices are negative and posi- tive, respectively. Another principal difference is the gas den- sity in these vortices. The upstream vortex involves motion of the quiescent air at room ...
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Citations
... This phenomenon is referred to as 'electric wind' or 'ionic wind' [5,21,22]. It leads to the formation and development of a starting vortex [23][24][25][26] or a directionally controllable wall jet [27,28]. Experimental data indicated that the time-averaged velocity induced by plasma can reach a few m·s −1 [5,6,11,18]. ...
In this study, a two-dimensional fluid model is employed to simulate the streamer, pressure wave, and vortex in surface dielectric barrier discharge driven by nanosecond pulse voltage (ns-SDBD). It comprises a numerical model with two interconnected modules: discharge dynamics and gas flow dynamics. These modules are coupled through the physical variables including ‘EHD force’, ‘thermal source’, ‘velocity field’, ‘gas temperature’, and ‘gas pressure’. Our research primarily focuses on the underlying physical mechanisms of pressure waves and vortices for plasma-based flow control. The generation of pressure waves is attributed to the rapid gas heating by pulsed discharge, whereas the formation and development of the vortex are related to the ionic wind (EHD effect) provided by the plasma. To thoroughly understand and optimize flow control performance, an investigation into the effects of various discharge parameters, such as voltage amplitude and polarity, is conducted. Additionally, multiple single SDBD modules are arranged in series, each featuring a dual three-electrode configuration. Subsequently, the dynamic behaviors of multiple streamers, pressure waves, and vortices, along with their interactions, are explored.
... Another method involves utilising the multi-sources excitation in a discharge reactor, such as AC energy significantly increases owing to the extra surface charge accumulated on the dielectric surface [29][30][31]. However, this enhanced discharge effect is observed during the initial several hundred cycles [32]. To remove the surface charge, the researchers have explored the discharge characteristics and application performance of the NS þ AC [32][33][34]. ...
... However, this enhanced discharge effect is observed during the initial several hundred cycles [32]. To remove the surface charge, the researchers have explored the discharge characteristics and application performance of the NS þ AC [32][33][34]. Compared to the sum of the ns pulse and AC discharges, the NS þ AC discharge exhibits an increased production of active radicals [35]. It is attributed to the neutralisation of the dielectric surface charge from the AC discharge by charged species generated by the ns discharge [36,37]. ...
A dual‐frequency (DF) dielectric barrier discharge, excited by the superposition of a 50 Hz low frequency (LF) and a 5000 Hz intermediate frequency (IF), is proposed to enhance discharge. The effect of the LF voltage component on the breakdown behaviour of the DF discharge during different periods has been studied both experimentally and numerically. The number of high‐current pulses rises as the LF voltage increases. The statistical analysis shows that the number of the current pulse amplitude above 80 mA in the DF discharge reaches nearly 6 times that in the IF discharge. Additionally, the total discharge energy in the DF discharge is significantly higher than that in the IF discharge. The simulation reproduces the temporal variation of the breakdown behaviours in the DF discharge. The simulated results reveal that the maximal electric field strength of the breakdown process is greater in the DF discharge compared to the IF discharge during a half‐period of DF. Finally, the comparison between the IF and DF discharges exhibits that the LF voltage regulates the accumulation of residual charged species on the dielectric surface after the breakdown by modulating the residual voltage between the air gap.
... 14 The concept of the separation of the power source into a repetitive pulse generator (for the ionization process) and DC or AC bias voltage generation (for the acceleration process) gradually spreads and is employed to induce ionic wind using DBDs. [15][16][17][18] The combination of these two power sources is considered to efficiently ionize air by using pulse voltage and efficiently accelerate charged particles. However, the optimal operation condition (e.g., pulse repetition frequency, pulse amplitude, bias voltage frequency, bias voltage amplitude, and electrode configuration) to argue that the above method is preferable compared to a conventional AC plasma actuator is still not clearly mentioned. ...
... A previous study also reported that the accumulated surface charge can be removed by switching the bias polarity, resulting in the performance improvement of the DBD plasma actuators. 15 The difference between the previous study and the current study is that the frequency of the repetitive pulses is comparable with the bias frequency in this study (the previous study employed a much higher frequency for the repetitive pulses compared to the frequency of the bias voltage). Our result indicates that when the frequency of the repetitive pulses is in the same order as the bias frequency, the delay time of the pulse became important for the ionic wind generation. ...
This study demonstrates the successful induction of a unidirectional ionic wind by adding an embedded electrode in a coplanar discharge, thus breaking the generation of a symmetrical electric field. The strategy for the ionic wind generation is based on separating the ionization process and the charged-particle acceleration process. Conventional plasma actuators used to induce an ionic wind typically incorporate exposed electrodes that pose a risk of unexpected airflow disturbance and reduce durability due to oxidation. However, the coplanar discharge-based, exposed-electrodeless plasma actuator developed in this study overcomes these issues. The coplanar discharge generates a diffused and uniform surface discharge, a desirable attribute for plasma actuators. The ionic wind velocity generated by this coplanar discharge plasma actuator is comparable to that generated by conventional plasma actuators when applying a square-waveform bias voltage to the additional electrode. Furthermore, this study emphasizes the significance of the phase difference between the repetitive pulses for generating coplanar discharge and the square-waveform voltage for accelerating the charged particles.
... This type of actuators, demonstrate superior effectiveness to the other types at high Reynolds and Mach numbers. The literature on experimental investigations of optical, electrical, thermal and mechanical characterizations of NS-pulsed DBDs is not very rich [9][10][11][12][13][14][15]; even fewer studies can be found on the numerical modeling of this process [16][17][18]. Comprehensive reviews on DBD applications in EHD can be found in [5,[19][20][21][22]. ...
A numerical algorithm is proposed for simulation of the AC-Dielectric Barrier Discharge plasma actuators including photo-ionization. The computational bottleneck related to a very long computing time has been circumvented by suppressing the discharge pulses and proposing the mean discharge model. It incorporates an artificial damping term into the electron transport equation to suppress the formation of pulses, which significantly accelerates the simulation. Based on the fluid description of three generic species: electrons, positive and negative ions, the model accounts for the drift, diffusion, and reaction terms. The reaction coefficients are extracted from the Boltzmann equation considering the local field approximation. A self-sustained discharge is achieved by including a Helmholtz model for photo-ionization during the positive voltage phase, and the secondary electron emission from the metal surface, during the negative voltage phase. The proposed methodology compromises the computational burdens of the first-principle approaches and inadequacy of the simplistic models in incorporating the problem physics. The accuracy of the proposed methodology has been validated by comparing the computational and experimental data for the electrical and flow characteristics of a laboratory actuator.
... This problem can be overcome by applying an AC voltage instead of a DC voltage to the third electrode. 53 Figure 8 shows the time evolution of the x velocity induced by actuator module B (d ¼ 12 mm) when a square waveform was applied to the third electrode. The amplitude and frequency were set to 10 kV and 10 Hz, respectively. ...
A novel dielectric barrier discharge (DBD) plasma-actuator module with an exposed electrode and two covered electrodes was developed to enhance electrohydrodynamic force generation based on the concept that it separates the ionization and acceleration processes. The conventional three-electrode configuration of the DBD plasma actuator suffers from unexpected spark discharge between the exposed electrodes, thereby failing to strengthen the electric field intensity for accelerating charged particles or generating a stable ionic wind. In this study, a third electrode was embedded in the dielectric layer to prevent spark discharge. Furthermore, an alternating current (AC) waveform was employed as the bias voltage, which was applied to the third electrode, instead of the direct current (DC) voltage used in a conventional DBD plasma actuator. Induced flow visualization using particle image velocimetry technique revealed that the DC bias voltage forms a weak ionic wind in the proposed DBD plasma actuator owing to the electric field screening effect, and the ionic wind periodically appears when the polarity of the voltage is reversed by applying an AC-bias voltage. The velocity of the ionic wind increases with increasing frequency and the AC bias voltage amplitude. Also, decreasing the distance between the second and third electrodes results in ionic wind enhancement. The results obtained in this study provide insights into the drastic improvement in the performance of DBD plasma actuators with the enhancement of the electric field intensity for charged particle acceleration.
... power units with respect to the produced plasma physicochemical properties have been the core of numerous studies [1]- [3]. According to the vast majority, the widely adopted modes for delivering electric power to DBD plasmas are the three following ones: 1) high-voltage sinusoidal waves; 2) highvoltage arbitrary pulses; and 3) high-voltage square pulses. ...
This report gives prominence to the importance of the traditional Cockcroft–Walton voltage multiplier to the design of pulsed power supplies for dielectric barrier discharge (DBD) applications. Following an inventive concept, a simple Cockcroft–Walton generator is combined with a MOSFET-based switch (in either “push” or “pull” mode). Thus, the to-be-chopped stabilized dc high voltage is produced by a compact, transformer-less, modular unit, having high flexibility in terms of engineering. This approach leads to well-defined, square, high-voltage pulses of variable amplitude, frequency, and duty cycle. Design, implementation, and proof test of such a prototype are here demonstrated. The prototype yields square pulses as high as 10 kV (plateau value), as narrow as 350 ns (variable pulsewidth up to millisecond, depending on the frequency), rising or falling time close to 20 ns, pulse repetition rates up to 4 kHz, and output mean power up to 150 W. The functionality of the system is demonstrated by driving coaxial, ambient air DBDs of variable lengths, while principal electrical and optical parameters are recorded. Peak power values higher than 70 kW are measured on the DBD side, while the voltage multiplier power efficiency factor remains close to 95%.
... During the last decade, various power supply technologies have been presented [7]. Sinusoidal [8,9], pulsed [10,11], and arbitrary [12,13] voltage waveforms are the most used. Among them, sinusoidal power sources are often preferred due to their inexpensiveness and robustness [2,5]. ...
Atmospheric-pressure plasma treatments for industrial and biomedical applications are often performed using Dielectric Barrier Discharge reactors. Dedicated power supplies are needed to provide the high voltage frequency waveforms to operate these nonlinear and time-dependent loads. Moreover, there is a growing technical need for reliable and reproducible treatments, which require the discharge parameters to be actively controlled. In this work, we illustrate a low-cost power supply topology based on a push–pull converter. We perform experimental measurements on two different reactor topologies (surface and volumetric), showing that open loop operation of the power supply leads to a temperature and average power increase over time. The temperature increases by ΔTvol~120 °C and ΔTsup~70 °C, while the power increases by ΔPvol~78% and ΔPsup~60% for the volumetric (40 s) and superficial reactors (120 s), respectively. We discuss how these changes are often unwanted in practical applications. A simplified circuital model of the power supply–reactor system is used to infer the physical relation between the observed reactor thermal behavior and its electrical characteristics. We then show a control strategy for the power supply voltage to ensure constant average power operation of the device based on real-time power measurements on the high voltage side of the power supply and an empirical expression relating the delivered power to the power supply output voltage. These are performed with an Arduino Due microcontroller unit, also used to control the power supply. In a controlled operation the measured power stays within 5% of the reference value for both configurations, reducing the temperature increments to ΔTvol~80 °C and ΔTsup~44 °C, respectively. The obtained results show that the proposed novel control strategy is capable of following the transient temperature behavior, achieving a constant average power operation and subsequently limiting the reactor thermal stress.
... The dielectric prevents the discharge current and the transition to an arc; however, at the same time, the electric field screening due to the surface charge could weaken the EHD force generation. A direct current (DC) or low-frequency AC biased repetitive pulses were proposed based on the strategy of the surface charge control [27,28]. A surface charge cycle with two strokes is formed when a DC-biased pulse voltage is applied: the positive-charging phase and neutralizing the positive charge phase, while the surface discharge driven by an AC voltage forms a four-stroke charge cycle [28]. ...
A relationship between electric potential distribution on a dielectric surface and electrohydrodynamic (EHD) force generation is experimentally investigated to improve the performance of dielectric-barrier-discharge (DBD) plasma actuators. Direct current (DC) biased repetitive pulses are applied to the DBD plasma actuator, which has two or three electrodes. Although the additional downstream exposed electrode has little effect on the electrical and optical characteristics of the DBD plasma actuator, the electric potential distribution strongly depends on the presence of the additional exposed electrode. Moreover, the saturation time of the surface charge is hundreds of milliseconds when the pulse repetition frequency is 5 kHz , showing a large difference in the time scale of surface DBD. We also demonstrated a significant improvement in the generation of ionic wind by adding an additional downstream exposed electrode owing to the prevention of the electric field screening. A concept that separates the ionization process and the acceleration process works properly for improving the performance of the DBD plasma actuators, but at the same time, the dynamics of the surface charge should be controlled so that a strong electric field is generated rather than the electric field being screened by surface charge.
... 23. Representation of the forces acting on the blade.Using Tecplot, the resultant force acting on the blade, in the direction of rotation was found to be 260.9 ...
... The residual positive charge deposited in the previous halfperiod (when the top electrode is anode) will probably play an essential, supportive, role in this scheme, as it can be accumulated over time in few millimetres distance from the top electrode edge [36] and create a virtual anode in the opposite half-period. The recombination of positive charges during the negative polarity is more effective close to the cathode, as shown in experimentally in [37] and theoretically in [18]. ...
We study the origin of filamentary patterns in a sinusoidally driven surface barrier discharge at high over-voltage in atmospheric pressure air. Using a time-correlated single-photon counting based optical emission spectroscopy, we reveal ultrafast processes within generated discharges in both polarities of the applied voltage. For negative polarity, we observe initiation of complex streamer cascade which emerges far from the bare cathode. This event is responsible for long filamentary structure detected by an intensified CCD camera and transfers an exceptionally large electrical charge. It constitutes another, previously unknown, mechanism contributing to the charge-transfer equilibrium in studied periodical discharge. The revealed process leads to the formation of an intense cathode spot, a critical condition for plasma-transition into a highly ionised state.
