Alan R. Hoskinson

Force measurements of single and double barrier DBD plasma actuators in quiescent air

We present the results of our experimental measurements of how variations in the discharge geometry of surface-mounted dielectric barrier discharges (DBDs) affect the force transferred to atmospheric pressure air. Our studies include both single barrier plasma actuators (one electrode insulated) and double barrier plasma actuators (both electrodes insulated) operated in quiescent air. Stagnation probe measurements of the induced air flow and direct force measurements using an electronic balance show that, for both actuator types, parallel time-averaged forces increase as the high voltage electrode diameter decreases. For single barrier actuators, this increase is exponential rather than linear as previously reported in the literature. The data from the two measurement techniques are directly proportional to one another. When the variation of velocity and pressure on all sides of an actuator are considered, the techniques show quantitative agreement.

Microdischarge propagation and expansion in a surface dielectric barrier discharge

We have recorded light emission from a surface dielectric barrier discharge with one exposed and one insulated electrode using an intensified digital camera. The discharge was operated in atmospheric pressure air. When the voltage to the exposed electrode is increasing, streamers form and propagate away from the exposed electrode in tens of nanoseconds. When the voltage is decreasing, more diffuse microdischarges form in a few nanoseconds. The qualitative behaviors of the plasma agree well with two-dimensional fluid simulations. Expansion in the average length of microdischarges as the applied voltage changes in both half-cycles of the waveform is also observed.

Comparisons of Force Measurement Methods for DBD Plasma Actuators in Quiescent Air

We have performed measurements of the force induced by both single (one electrode insulated) and double (both electrodes insulated) dielectric barrier discharge plasma actuators in quiescent air. We have shown that, for single barrier actuators with cylindrical exposed electrodes, as the electrode diameter decrease the force efficiencies increase much faster than a previously reported linear trend. This behavior has been experimentally verified using two different measurement techniques: stagnation probe measurements of the induced flow velocity and direct measurement of the force using an electronic balance. Actuators with rectangular cross-section exposed electrodes do not show the same rapid increase at small thicknesses. We have also shown that the induced force is independent of the material used for the exposed electrode. The same techniques have shown that the induced force of a double barrier actuator increases with decreasing narrow electrode diameter.

Flow measurements and plasma simulations of double and single barrier DBD plasma actuators in quiescent air

In recent years, interest has grown in using surface-mounted dielectric barrier discharges (DBDs) as aerodynamic actuators. We present the results of our experimental and computational studies of how variations in discharge geometry aect the induced electro-hydrodynamic (EHD) force. Our studies include both single barrier actuators (one electrode insulated) and double barrier actuators (both electrodes insulated). Pitot tube measurements of the ow velocity induced in quiescent air show that, for both actuator types, parallel time-averaged forces increase as the high voltage electrode diameter decreases. Our uid plasma simulation, which models a reduced geometry, predicts some characteristics of the experimental discharge, but does not fully reproduce the experimental trends of the parallel force with changing electrode diameter.

2-D Simulations of Single and Double DBD Plasma Actuators with Finite Electrode Thicknesses

We have performed 2-dimensional fluid simulations of singleand double-barrier plasma actuators with varying actuator and electrode sizes operating in an air-like mixture of gases. We examine the effects of finite electrode thickness on both plasma generation and the force induced on the gas. Two series of simulations have been completed: full-scale actuators with dimensions comparable to those used in experiments, and reduced-scale actuators a factor of 10 smaller in all dimensions. Negative ions are seen to play a much stronger role in the full-scale simulations of both geometries compared to the reduced-scale runs. Relatively long periods of inactivity are observed for single-barrier actuators with large exposed electrodes, leading to lower forces for these actuators. Simulations of double barrier actuators show only a small dependence on the diameter of the narrow electrode.

Optical characteristics of double and single surface dielectric barrier discharges

Asymmetric double (both electrodes insulated) and single (one electrode insulated) surface barrier discharges are investigated. Both geometries used one wire electrode and one copper tape electrode. The discharges are driven by 1 kHz symmetric triangle waveforms. Time- and space-resolved light emissions are recorded by an intensified charge-coupled device (ICCD) camera, with a minimum exposure time of 2 ns. In the single-barrier geometry, filamentary plasmas are observed when the voltage on the exposed electrode is increasing, and “diffuse” jet-like plasma are observed when the voltage is decreasing. In the double-barrier geometry, both structures are observed simultaneously, but in opposite directions, in all plasmas. Additional similarities will be discussed.

Double DBD Plasma Actuator Simulations and Experiments in Quiescent Air

Summary form only given. We have investigated surface dielectric barrier discharges with both electrodes insulated. Our experiments with such double barrier actuators have shown that flow is induced in quiescent air from a narrow electrode towards a wide one. The series of observed current peaks suggest a strongly filamentary plasma. Fluid simulations indicate that the net force exists because the plasma is prevented from propagating beyond the edge of the narrow electrode. The intense peaks in the device current are the result of rapid gas breakdown above the dielectric surface. Sawtooth waveforms have similar effects on the flow induced by double barrier actuators to those observed in single barrier devices. We present the results from a study examining the variations of induced force as several geometric dimensions of the actuator change. We compare the forces observed in experiments and predicted by simulation for each actuator geometry. The dimensions compared include narrow electrode size, electrode gap spacing, and others.

Experimental comparison of atmopsheric pressure plasma actuator geometries

Summary form only given. In this study we examine two configurations for the asymmetric surface barrier plasma actuator. This discharge is designed to generate air flow near its surface, and has been shown, when placed on a surface, to increase the angle of attack at which flow separation occurs. Such a device could be used as a virtual flap by controlling flow over an airplane wing. The configurations studied include systems with one exposed electrode above the dielectric surface and one sealed electrode below and two encapsulated electrodes below the surface. We present data describing the light emission, current-voltage characteristics, and induced air flow of each discharge

Effect of Finite Length on the Current-Voltage Characteristic of a Cylindrical Langmuir Probe

Summary form only given. Cylindrical Langmuir probes are widely used in a variety of applications. Nevertheless, many non-ideal characteristics have not been fully investigated. In this work, we examine the relationships between probe length, radius, and plasma Debye length and their effect on experimentally obtained I-V curves. The plasmas investigated are low pressure weakly collisional plasmas generated by hot filaments. Plasma density and temperature errors due to these measurements are estimated for several different fitting methods. Probe construction methods to limit the non-idealities are suggested