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Via numerical simulation, the structure and characteristics of a diffuse barrier discharge are studied in air under atmospheric pressure in a system of planar electrodes, one of which is covered with a dielectric. Electrons, positive and negative ions, processes of ionization, recombination, attachment, detachment, and photoionization, dielectric charging, and the autoemission of electrons from the electrode are studied. To determine the structure of the diffuse barrier discharge, the voltage pulses are considered with a leading-edge time of 1 and 100 ns and a rate of rise of the electric-field strength of 152 and 1.52 kV/(cm ns) with a duration of 2 and 500 ns, respectively. The one-dimensional structure of the barrier discharge is described. It is similar to a streamer and is conventionally called a flat streamer: a planar wave of ionization with plasma channel located behind its front and a nonconducting gas before it. The diffusive discharge is usually opposed the streamer discharge, but this work corrects this concept. The main stages of the formation of the diffuse barrier discharge are obtained: the avalanche stages, the avalanche–streamer transition, the propagation of positive and negative heads of the streamer, the head shorting to electrodes, and the process of plasma relaxation. It is shown that the plasma relaxation process after voltage decreasing is slow and that the rate of front rise and pulse duration significantly influence the discharge structure and parameters. Considering an external electric circuit in the model restricted the current in the system and provided satisfactory quantitative agreement with experiment. [ABSTRACT FROM AUTHOR]

So far, electrohydrodynamic (EHD) pumps based on the injection or the field-enhanced dissociation (the Wien effect) at the surface of metal electrodes have been studied. This paper proposes and studies both numerically and experimentally a fundamentally new pump scheme, namely, the EHD pump operating due to the Wien effect in a conical hole located in the solid insulation barrier. An experimental setup of the pump has been created, and performance (pressure vs flow rate) characteristics have been measured that satisfactorily agree with the results of computer simulation. With the size of the hole being a fraction of a millimeter, the proposed system performance is comparable to that of the previously studied EHD pumps. [ABSTRACT FROM AUTHOR]

The structure of electrohydrodynamic (EHD) flows in a variable electric field has been investigated based on computer simulation of EHD flows in a needle–plane electrode system. The characteristic frequency interval of a feed sine-wave voltage with an amplitude of 5 kV has been considered. Changes in the charge and velocity structures of EHD flows are described, and the characteristic features of the flows versus feed voltage frequency are presented. The periodicity of such EHD flows is demonstrated. [ABSTRACT FROM AUTHOR]

We have investigated experimentally the cooling of a heated plate playing the role of a grounded electrode by a narrow intense ionic wind jet produced by a needle electrode and directed along the normal at the plate center. For a fixed average temperature of the heater, we have obtained the dependence of the heat power removed with the wind on the electric power spent for sustaining the corona discharge for various interelectrode distances and voltages. It is shown that a small ionic wind jet can effectively cool a massive plate, removing up to 23 W of heat power for a spent electric power of up to 0.7 W. We have also studied experimentally the structure of ionic wind in the electrode system considered. A laser anemometry setup was used for visualizing the flow and for obtaining velocity distributions. The velocities in the central jet of ionic wind reached 8–9 m/s. The jet was narrower and faster for the positive polarity of the corona discharge. However, the efficiency of cooling for positive and negative polarities was approximately the same. [ABSTRACT FROM AUTHOR]

A sphere–plane electrode system in the air with one or two dielectric sheet barriers arranged perpendicularly to a grounded plane is considered. Hence, the barriers do not obstruct the shortest path between the electrodes. The effect of the barriers on streamer processes and breakdown is studied. It has been revealed that the breakdown voltage generally decreases, when the barrier–electrode distance is reduced. [ABSTRACT FROM AUTHOR]

The effect of electric wind produced by a positive corona discharge on the air flow around a circular cylinder at Reynolds numbers of 2400 and 3200 is investigated. The geometry of cylinder–wire electrodes is considered for two positions of the corona electrode relative to the cylinder: one wire behind the cylinder and two symmetrical wires above and below the cylinder. A direct numerical simulation of the electrohydrodynamic problem is performed using an original unipolar model of the corona discharge. The effect of a thin jet of electric wind directed from the corona electrode to the cylinder on the structure of the vortex wake behind the cylinder and the drag force is considered. It is shown that, when two corona electrodes are located above and below the cylinder, the electric wind prevents the formation of a Karman vortex street and significantly reduces the air drag of the cylinder. If the discharge electrode is located behind the cylinder, the corona discharge and the electric wind lead to the formation and development of large vortices in the wake behind the cylinder, which leads to significant fluctuations in its air drag. It is shown that a corona discharge significantly changes the characteristics of the Karman vortex street: as the voltage increases to 30 kV, the vortex shedding frequency decreases by a factor of 2.5 and the sizes of the vortices and their rotation velocity noticeably increase. The drag force is quasi-periodic and its mean value linearly depends on the corona voltage. [ABSTRACT FROM AUTHOR]

We have solved the problem of injection-type through electrohydrodynamic (EHD) flow in a closed channel. We have considered a model of a liquid with four types of ions. It is shown that a through EHD flow without internal vortices in the electrode gap is formed for the ratio 2 : 1 of the initial injection current from the electrodes in the channel. The structure of the flow in different parts of the channel and the integral characteristics of the flow have been analyzed. It is shown that for a quadratic function of injection at the electrodes, the current-voltage characteristic of the flow is also quadratic. [ABSTRACT FROM AUTHOR]

Electrohydrodynamic (EHD) flows emerge in dielectric liquids under the action of the Coulomb force and underlie energy-efficient techniques for heat and mass transfer. The key issue in the phenomena is the way how the net charge is created. One of the most promising, yet poorly studied charge formation mechanisms is the field-enhanced dissociation (or the Wien effect). So the paper studies an EHD flow caused solely by the effect by virtue of both experiment and computer simulation. To preclude the competing mechanism of charge formation--the injection--a new EHD system of a special design was examined. Its main feature is the use of solid insulation to create the region of the strong electric field far from the electrode metal surfaces. The experimental study used the particle image velocimetry technique to observe velocity distributions, whereas the computations were based on the complete set of electrohydrodynamic equations employing the commercial software package COMSOL Multiphysics. Spatial distributions of key quantities (including the ion concentrations, the total space charge density, and the velocity) and the acting forces were obtained in the computer simulation and were analyzed. The experimental flow structure was observed for a number of voltages up to 30 kV. The comparison of the numerical and experimental results yielded a good quantitative agreement for strong electric fields though some overshoot was observed for weak ones. The results allow concluding on the applicability of the Onsager theory of the field-enhanced dissociation in the context of EHD flows. [ABSTRACT FROM AUTHOR]

The paper presents the technique for computing current?time characteristics of the transient regime, taking place after the pulsed application or change of high voltage, and dynamical current?voltage ones obtained with the voltage sawtooth modulation. The basis of the simulation is the complete set of electrohydrodynamic equations with both the convective and the migration mechanisms of charge transport being taken into account jointly. The numerical calculations were performed using commercial software package COMSOL Multiphysics based on the finite element method. The simulation was carried out for the needle?plane electrode system. The unsteady-state current passage processes, including electrohydrodynamic flow formation, were calculated. The interrelation between the latter and the total current passing through the electrical circuit were investigated. The shape and features of the current?voltage characteristics obtained with the voltage sawtooth modulation were shown to be dependent on the mechanism of charge formation. The qualitative comparison between the simulated dynamical current? voltage characteristics and the original experimental data has shown a good agreement. [ABSTRACT FROM AUTHOR]

The current passage through a low-conducting liquid is simulated for a system of electrodes with a highly nonuniform electric-field distribution at voltages lower and higher than the threshold of appearance of electrohydrodynamic flows. The structure of the near-electrode dissociation-recombination charged layers is considered in terms of the following two-charge formation models: constant dissociation in the volume but without injection and injection from an electrode and constant dissociation in the volume. The change in the polarity of the near-electrode charged layer caused by an increase in the voltage or a change in the low-voltage conductivity of the liquid is analyzed. Two types of electrohydrodynamic flows, which appear in real electrohydrodynamic devices and have opposite directions, are obtained using one mathematical model. [ABSTRACT FROM AUTHOR]

We report on the results of experimental investigation of a pulsed corona discharge in electric fields with different degrees of nonuniformity under the action of a standard thunderstorm pulse in a wide range of voltages from the origination threshold to the breakdown. A high-sensitivity video camera makes it possible to record microdischarge and streamer processes in air long before the spark breakdown. It is known that the size of the corona discharge sheath increases with the supplied voltage, and the shape of the corona sheath depends on the polarity of the active electrode [1, 2]. It was demonstrated for the first time by Peek [3] that the range of voltages from the initiation of a corona discharge to the spark breakdown increases with the degree of nonuniformity of the electric field. We show that an analogous pattern is observed for a pulsed corona also. Our results show that the form of a pulsed corona discharge considerably depends on the pulse polarity, and a spark breakdown becomes possible when most branches in the streamer corona cover the electrode gap. [ABSTRACT FROM AUTHOR]

Complex investigation of the structure of electrohydrodynamic (EHD) flows in a needle-plane electrode system is carried out on the basis of analysis of experimental data and the results of computer simulation. An algorithm of iterative simulation of the volume charge distribution in a fluid is developed. Simulation is carried out using the ANSYS system. The fields of velocities and pressures, as well as electric characteristics of EHD flows, are calculated. Analysis of the results reveals a number of features of EHD flows in the electrode system under investigation. Peculiarities of the band structure are determined, and the characteristic size of the low-pressure zone near the active electrode, as well as the sizes of the acceleration and deceleration zones of the fluid in the electrode gap, is determined. [ABSTRACT FROM AUTHOR]

Computer simulation is carried out for the process of formation of electrohydrodynamic flows emerging in a system of two parallel wires as a result of symmetric injection from each electrode (2D case). Simulation is performed using the ANSYS system. A simulation algorithm is developed for nonstationary electrohydrodynamic flows. The results of simulation are presented. Analysis of the results shows that the evolution of electrohydrodynamic flows is accompanied by the formation of thin oppositely charged liquid streams moving in opposite direction from near-electrode charged layers. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

Computer-aided simulation of the electrohydrodynamic flow pattern in an asymmetric system of electrodes (configured as “narrow depression under plane” or “blade above plane”) is carried out. The objective of the simulation is to reveal a correspondence between the kinematic flow pattern and the distribution of driving (Coulomb) forces. The kinematic pattern of the flow simulated is compared with the results of experimental data processing. Good agreement between the simulation results and experimental data is found. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

The patterns of velocity and acceleration distribution in an electrohydrodynamic through flow in a symmetric system of electrodes have been experimentally studied. Analysis of the main features in the kinematic and dynamic flow structures provides information on the distribution of space charge and the course of events in the recombination zone. It is established that the recombination zone extends beyond the interelectrode space. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

A specially designed program package is used for the visualization of experimental data for 2D electrohydrodynamic flows in geometrically symmetric (wire-wire) and asymmetric (wire over plane) electrode systems. The velocity and acceleration distributions in the flows are obtained. The influence of the passive electrode on the kinematic and dynamic structures of the electrodynamic flows is revealed by comparing the results obtained for both electrode systems. A recombination zone is separated and studied. [ABSTRACT FROM AUTHOR]

A study of the structure of electrohydrodynamic flows shows that the electric charge carriers are ions that are practically frozen into the surrounding liquid. In other words, ions in weakly conducting liquids are capable of forming more or less stable structures whose viscoelastic properties are different from those of an uncharged liquid. One method of studying this effect is to investigate the velocity dispersion of ultrasound on charged supermolecular formations. The results of theoretical and experimental investigations of acoustic dispersion in liquid dielectrics subjected to prebreakdown electric fields are presented. A model problem of sound propagation in a liquid in which supermolecular structures have formed around elementary charge carriers is studied theoretically. Approximate formulas describing the dispersion of the acoustic phase velocity as a function of the electric field parameters and the electrophysical parameters of the liquid are obtained. The frequency dependence of the sound velocity is of a resonance character, the resonance frequency being determined by the electric charge density and the mass of the charged supermolecular structures. The experiments showed that the space charge affects the velocity of acoustic waves in liquid dielectrics. [ABSTRACT FROM AUTHOR]