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Magnetic Resonance Imaging Physical Principles And Sequence Design

Several studies have shown that a surface dielectric barrier discharge (DBD) may be used as an electrohydrodynamic (EHD) actuator in order to control airflows In this paper, a parametric study has been performed in order to increase the velocity of the ionic wind induced by such actuators The results show that an optimization of geometrical and electrical parameters allows us to obtain a time-averaged ionic wind velocity up to 8 m/s at 05 mm from the wall Moreover, non-stationary measurements of the induced wind have been performed with synchronized records of current and voltage signals These experiments show that the DBD actuator seems to generate a pulsed velocity at the same frequency than the applied high voltage

Optimization of a dielectric barrier discharge actuator by stationary and non-stationary measurements of the induced flow velocity: application to airflow control

Dielectric Barrier Discharges (DBDs) are plasmas generated in configurations with an insulating (dielectric) material between the electrodes which is responsible for a self-pulsing operation. DBDs are a typical example of nonthermal atmospheric or normal pressure gas discharges. Initially used for the generation of ozone, they have opened up many other fields of application. Therefore DBDs are a relevant tool in current plasma technology as well as an object for fundamental studies. Another motivation for further research is the fact, that so-called partial discharges in insulated high voltage systems are special types of DBDs. The breakdown processes, the formation of structures, and the role of surface processes are currently under investigation. This review is intended to give an update to the already existing literature on DBDs considering the research and development within the last two decades. The main principles and different modes of discharge generation are summarized. A collection of known as well as special electrode configurations and reactor designs will be presented. This shall demonstrate the different and broad possibilities, but also the similarities and common aspects of devices for different fields of applications explored within the last years. The main part is devoted to the progress on the investigation of different aspects of breakdown and plasma formation with the focus on single filaments or microdischarges. This includes a summary of the current knowledge on the electrical characterization of filamentary DBDs. In particular, the recent new insights on the elementary volume and surface memory mechanisms in these discharges will be discussed. An outlook for the forthcoming challenges on research and development will be given. Page 1 of 47 AUTHOR SUBMITTED MANUSCRIPT PSST-101368.R1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A cc ep e M nu sc rip t Progress on DBD Sources and Filaments 2

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Dielectric barrier discharges: progress on plasma sources and on the understanding of regimes and single filaments

The present paper is a wide review on AC surface dielectric barrier discharge (DBD) actuators applied to airflow control. Both electrical and mechanical characteristics of surface DBD are presented and discussed. The first half of the present paper gives the last results concerning typical single plate-to-plate surface DBDs supplied by a sine high voltage. The discharge current, the plasma extension and its morphology are firstly analyzed. Then, time-averaged and time-resolved measurements of the produced electrohydrodynamic force and of the resulting electric wind are commented. The second half of the paper concerns a partial list of approaches having demonstrated a significant modification in the discharge behavior and an increasing of its mechanical performances. Typically, single DBDs can produce mean force and electric wind velocity up to 1 mN/W and 7 m/s, respectively. With multi-DBD designs, velocity up to 11 m/s has been measured and force up to 350 mN/m.

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Electrical and mechanical characteristics of surface AC dielectric barrier discharge plasma actuators applied to airflow control

The combined dynamics of swirler and turbulent premixed swirling flames

Capacitance and power consumption quantification of dielectric barrier discharge (DBD) plasma actuators

In the present work artificially excited Tollmien–Schlichting (TS) waves were cancelled using plasma actuators operated in pulsed mode. In order to achieve this a vibrating surface driven by an electromagnetic turbulator was flush mounted in a flat plate to excite the TS waves. These were amplified by an adverse pressure gradient induced by an insert on the upper wall of the test section. A control plasma actuator positioned downstream of the excitation actuator attenuates the waves by imparting an unsteady force into the boundary layer to counteract the oscillation. As a result the amplitude of the velocity fluctuations at the excitation frequency is reduced significantly depending on the distance from the wall. A parameter study was performed to identify the influence of several operation parameters of the control actuator.

Active cancellation of artificially introduced Tollmien-Schlichting waves using plasma actuators

In the present work plasma actuators were applied in a flat-plate boundary layer with an adverse pressure gradient to influence the transition of the boundary layer. The first actuator downstream of the leading edge is operated in pulsed mode to introduce perturbations into the boundary layer to promote transition. Two steady operating actuators further downstream damp the perturbations significantly, which results in transition delay.

Experimental transition delay using glow-discharge plasma actuators

Towards In-Flight Applications? A Review on Dielectric Barrier Discharge-Based Boundary-Layer Control

A new procedure of determining the time resolved capacitance of a plasma actuator during operation is introduced, representing a simple diagnostic tool that provides insight into the phenomenological behavior of plasma actuators. The procedure is demonstrated by presenting example correlations between consumed electrical energy, size of the plasma region, and the operating voltage. It is shown that the capacitance of a plasma actuator is considerably increased by the presence of the plasma; hence a system that has previously been impedance matched can be considerably de-tuned when varying the operating voltage of the actuator. Such information is fundamental for any attempts to increase the energy efficiency of plasma-actuator systems. A combined analysis of the capacitance, light emission, size of the plasma region, force production, and power consumption is presented.

Sven Grundmann

Papers

Capacitance and power consumption quantification of dielectric barrier discharge (DBD) plasma actuators

Active cancellation of artificially introduced Tollmien-Schlichting waves using plasma actuators

Experimental transition delay using glow-discharge plasma actuators

Towards In-Flight Applications? A Review on Dielectric Barrier Discharge-Based Boundary-Layer Control

Power consumption, discharge capacitance and light emission as measures for thrust production of dielectric barrier discharge plasma actuators