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This paper provides a comprehensive analysis of the viscous effects for the DBD operation. Maximum DBD induced flow velocity is estimated based on the conservation laws without the viscous effects. It is demonstrate d that inclusion of the viscosity leads to the twice smaller maximum DBD induced flow velocity. The possibility to increase maximum induced flow velocity by use of a series of DBDs is considered. The significant dependence of the DBD induced flow on the spatial distribution of the DBD body force is shown. Based on the study of the boundary layer profile , it is demonstrated that the DBD force should not only be maximized, but also generated at the optimum location for optimum DBD performance. The possibility of using DBD as a de-icing device is also analyzed.

In this paper, we study the surface plasma induced jets using analytical self-similar solution for the viscous wall jet problem. It is shown that the entire induced flow field outside the plasma can be found from the velocity profile measured in a single streamwise location. Analytical expressions for key plasma induced flow characteristics are found. The analytical model’s applicability to the dielectric barrier discharge (DBD) plasma actuators is validated experimentally.

Surface charge buildup and its effect on performance of DBD plasma actuators driven by repetitive voltage pulses added to dc bias were studied. A simplified numerical model showed a good agreement with the experimental data. This confirms that the surface charge is deposited by the ions which drift from the plasma region to the dielectric surface in the applied bias field . Based on the results of surface charge studies, a new configuration of the DBD plasma actuators was proposed – an asymmetric DBD plasma actuator with a slightly conductive dielectric that would deplete the surface charge between the pulses. Two materials that have been considered as slightly conductive dielectrics – zinc oxide and linen based phenolic, showed some promise, but one was too conductive, and the other too resistive. Further search for suitable materials could potentially improve performance of plasma actuators.

An effective parallel comprehensive, physically based numerical model of an asymmetric dielectric barrier discharge (DBD) plasma actuator in air, which takes into account the photoionization mechanism, has been developed for multiprocessor computations. Using the developed model the propagation of the cathodedirected streamer driven by 4ns positive pulse has been analyzed. The streamer parameters have been compared to ones computed using the concept of artificial plasma generation. It has been shown that the streamer, computed based on the photoionization model, is several times thicker than one computed based on the artificial plasma. The maximum electric field at the streamer head is lower for the case of photoionization.

Based on the early developed single-processor numerical model for the dielectric barrier discharge simulation we have developed a multi-processor model. The time required for the DBD simulation is shown to be significantly less for the multiprocessor model than for the single-processor one. Based on the understanding of the physics of the DBD, operated with nanosecond pulses and bias voltage, we have implemented a modified time step for the plasma kinetic calculation between the breakdowns. This approach has provided a 3-orders of magnitude increase in the speed of computations between pulses. Using the multi-processor model with modified time step a 4kV, 4ns positive pulse with 1kV DC bias has been simulated on 32 processors. The qualitative results are in agreement with previously obtained results for lower voltages, however the speed of computation has significantly increased.

A parallel comprehensive, physically based numerical model of an asymmetric dielectric barrier discharge (DBD) plasma actuator in air has been developed for multi-processor computations. Based on the numerical model for DBD simulations, a model has been also developed which allows the computation of the charge distribution on the dielectric surface of DBD using the experimentally obtained electric potential distribution. The surface charge motion has been analyzed, and a theory of charge motion on the dielectric surface has been developed. It is concluded that the main negative charge carriers on the surface are negative ions.

DBD plasma actuators driven by repetitive nanosecond pulses added to low frequency bias voltage are studied, and parametric results of plasma-induced thrust versus voltage profile parameters are presented. The results of the thrust measurements agree with schlieren visualization results obtained earlier and indicate that dielectric surface charge plays a major role in the thrust. Direct measurements of the dielectric surface potential and its dynamics show that charge builds up at the dielectric surface and extends far downstream of the plasma. For a sinusoidal voltage waveform, the dielectric surface charges positively. With the voltage waveform consisting of nanosecond pulses superimposed on a dc bias, the sign of the dielectric surface charge is the same as the sign (polarity) of the bias voltage. Based on the surface charge measurements, a modified configuration of DBD plasma actuator is proposed. Preliminary experiments show its effectiveness at relatively low voltages. Variations of the permittivity of dielectric with temperature and frequency were also considered in relation to their role in DBD actuator performance.

An earlier developed detailed physical model of an asymmetric dielectric barrier discharge (DBD) plasma actuator in air driven by repetitive nanosecond voltage pulses and ac/dc bias is used to model realistic experimental conditions, such as nonideal pulses with multiple reflections. The force and heating rate calculated by the plasma model is used as an input to two-dimensional viscous flow solver to predict the time-dependent DBD-induced flowfield. The calculations reproduce the wall jet and vortices observed in experiments and enable determination of the induced flow velocity at the plasma edge and the body force magnitude from the schlieren imaging. A three-electrodes DBD system is theoretically explored, and its advantages are shown to only exist during a very short time following the voltage pulse.

A theoretical and experimental investigation of the Rayleigh-Taylor instability stabilization in the multi-layer liquid system using high frequency oscillations was carried out. The stabilization criterion for a layer of deep liquid, confined by air, was derived to coincide with stabilization criterion for the deep liquid above air. For a narrow layer of liquid the stabilization parameters depend only on the layer depth, but not on a wave vector. The possibility of the Saffman-Taylor instability stabilization in the Hele-Show cell using an alternating pressure was shown. The theoretical dependence of the alternating pressure amplitude on its frequency to stabilize the Saffman-Taylor instability was derived. These results may be useful for stabilization of instabilities in plasma and during mineral oil production. The problems of the Rayleigh-Taylor instability (RTI) come across in different physics fields, such as hydrodynamics, plasma physics and astrophysics. The theory of the hydrodynamic RTI is described in [1-3] for liquids in the systems of plane, cylindrical and spherical geometries under external forces and pressure gradients. The effects of liquid viscosity and spatial inhomogeneity were taken into account. The stability conditions for different cases are obtained and the nonlinear dynamics of the RTI on liquid boundaries are analyzed. The asymptotic behavior for the nonlinear stage of the RTI was investigated using the Fourier-series expansion [4,5]. A number of the experimental researches of the nonlinear and chaotic RTI dynamics [6-9] and the RTI dynamics in inertial confinement fusion [10-12] were carried out. Another example of the hydrodynamic instability is the Saffman-Taylor instability (STI). It arises on the boundary between two viscous liquids, when the less viscous one pushes the more viscous one in porous media, and consists in the development of transverse perturbations of the displacement front. The nonlinear stage of these perturbations results in the formation of so called “viscous fingers”. The problem of appearance of the viscous fingers in the Hele-Show cell is associated with the STI in porous media. The similarity between these phenomena was noticed by Paterson in [13]. The extensive theoretical, experimental and numerical investigations of the STI for different liquid systems, such as multi-layer systems or systems with mixed layer, were carried out [14-18]. In many practical problems the RTI and the STI development should be suppressed. For example, one way of the increase of mineral oil production from depleted oil field is an injection of water under the oil region and oil extrusion by the water. Since the water viscosity is less than the oil one, the STI arises on the displacement front between the water and the oil. This instability leads to the water outbreak through the oil and oil production stops. Therefore the question of its stabilization arises. There are different ways to stabilize the RTI and the STI. It is possible to use a magnetic field to suppress the RTI in plasma [19] or an oscillating magnetic field to stabilize conductive heavy liquid supported against gravity [20]. The RTI of the boundary between two liquids of different densities can be stabilized using high-frequency oscillations [21]. In that paper the theoretical model of the RTI stabilization for two “infinitely deep” ideal liquids using the Kapitza method [22] was developed as well as the number of experiments on stabilization of the RTI in the cylindrical geometry were carried out. A theory of the stabilization of the RTI is also developed using the Floquet method [2,23]. A goal of the present paper is a theoretical investigation of the stabilization of the RTI in the system of three layers of liquids in plane geometry, theoretical investigation of the stabilization of the STI in the Hele-Show cell and carrying out the experiment on stabilization the inverted vessel with liquid and layer of liquid, confined within the air. In contrast to the earlier researches on the hydrodynamic instabilities stabilizations, in which the systems with only single boundary between liquids were taken into consideration, the present paper demonstrates theoretical and experimental possibilities of the stabilization of the coupled waves systems.