Dmitry Opaits

Experimental investigation of dielectric barrier discharge plasma actuators driven by repetitive high-voltage nanosecond pulses with dc or low frequency sinusoidal bias

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 matching to the plasma, a numerical code for short pulse calculations with an arbitrary impedance load was developed. A new approach for nonintrusive diagnostics of plasma actuator induced flows in quiescent gas was proposed, consisting of three elements coupled together: the schlieren technique, burst mode of plasma actuator operation, and two-dimensional numerical fluid modeling. The force and heating rate calculated by a plasma model was used as an input to two-dimensional viscous flow solver to predict the time-dependent dielectric barrier discharge induced flow field. This approach allowed us to restore the entire two-dimensional unsteady plasma induced flow ...

Surface charge in dielectric barrier discharge plasma actuators

Direct measurements of the dielectric surface potential and its dynamics in asymmetric dielectric barrier discharge (DBD) plasma actuators show that the charge builds up at the dielectric surface and extends far downstream of the plasma. The surface charge persists for a long time (tens of minutes) after the driving voltage has been turned off. 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. The surface charging significantly affects DBD plasma actuator performance.

Experimental Investigation of DBD Plasma Actuators Driven by Repetitive High Voltage Nanosecond Pulses with DC or Low-Frequency Sinusoidal Bias

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 matching to the plasma, a numerical code for short pulse calculations with an arbitrary impedance load was developed. A new approach for non-intrusive diagnostics of plasma actuator induced flows in quiescent gas was proposed, consisting of three elements coupled together: the schlieren technique, burst mode of plasma actuator operation, and 2-D numerical fluid modeling. This approach allowed us to restore the entire two-dimensional unsteady plasma induced flow pattern as well as characteristics of the plasma induced force. The experiments and computations showed vortex flow structures induced by the actuator. Parametric studies of the vortices at different bias voltages, pulse polarities, peak pulse voltages, and pulse repetition rates were conducted. The significance of charge build-up on the dielectric surface was demonstrated. Based on the observations, a new voltage waveform, consisting of high-voltage nanosecond repetitive pulses superimposed on a highvoltage low-frequency sinusoidal voltage, was proposed. Advantages of the new voltage waveform were demonstrated experimentally.

Numerical modeling of DBD plasma actuators and the induced air flow.

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.

Time-resolved measurements of plasma-induced momentum in air and nitrogen under dielectric barrier discharge actuation

There has been much recent interest in boundary layer (BL) actuation by offset surface dielectric barrier discharges (SDBD). These discharges either act directly on the gas momentum through the mechanism of charge separation or they increase the flow stability through the creation of disturbances to the BL at a particular frequency. The objective of the work reported here is to clarify the physical mechanism of plasma-flow interaction. Two problems are considered in detail: the exact spatial/temporal distribution of the plasma-related force, and the specific role of negative ions in the net force budget. The experiments were made with an offset electrode configuration of SDBD at voltage amplitude U≤12 kV and frequency f=0.02–2 kHz. The main data were obtained by time-resolved Pitot tube pressure measurements in air and nitrogen at atmospheric pressure. Three main features of SDBD behavior were considered. First, the strong inhomogeneity in the spatial distribution of the plasma-induced flow were detected....

Electrodynamic effects in nanosecond-pulse-sustained long dielectric-barrier-discharge plasma actuators

Both numerical and experimental studies of the voltage distribution in a pulsed long dielectric barrier discharge plasma actuator have been performed. The results demonstrate the importance of electrodynamic effects in actuators for which the length is comparable with the length of the propagating pulses. These effects lead to a nonuniform voltage distribution along the electrodes, voltage doubling at the end of the actuator, nonoptimized power coupling to the actuator, and ringing. In addition to the direct voltage measurements, images of the discharge were taken which revealed its nonuniform structure.

Limitations of the DBD effects on the external flow

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.

Improving Thrust by Suppressing Charge Build-up in Pulsed DBD Plasma Actuators

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.

Surface plasma induced wall jets

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.

The role of the photoionization in the numerical modeling of the DBD plasma actuator.

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.