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Sherman 1998). Then, different groups already having background experiences on corona discharges and their interactions with quiescent or moving flows formed a new highly motivated community that contributes to the dissemination of the advantages and relevancy of non-thermal plasma discharges as an alternative to conventional flow actuators (Moreau 2007;Corke et al. 2009Corke et al. , 2010. Rapidly, the number of publications in journals and conference exponentially grows to finally become a full interdisciplinary research field. The sudden interest for surface dielectric barrier discharge (DBD) energized by AC high voltage for manipulating airflows was initially motivated by the easy implementation of these actuators and a possible retrofitting on existing airfoils. They have the capability to be mounted at the surface of linear or curved objects with a minimal protrusion in the flow. Beside, their location can be changed faster than other active actuators that require a new model for each new position of actuation. The amplitude and frequency of the electrohydrodynamic (EHD) force produced by the surface plasma are directly connected to the driven electrical signal, this being a clear advantage for parametric studies on the sensibility of one flow to well-defined perturbations. Indeed, the EHD force (also referred as EFD force for electro-fluid dynamic) and the resulting produced flow called electric wind or ionic wind are due to electric field that acts on charged species. These charged species are produced by physical phenomena such as ionization, recombination, attachment, detachment and photoionization, which occur at timescale of a few picoseconds (Boeuf et al. 2009a). Subsequently, the produced body force, despite being low-pass filtered by fluid mechanical laws (viscosity, energy exchanges, dissipation) to produce electric wind, has a high bandwidth. Plasma actuators, and more specifically dielectric barrier discharge actuators, have demonstrated their authority to Abstract 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.

Flow control consists of manipulating flows in an effective and robust manner to improve the global performances of transport systems or industrial processes. Plasma technologies, and particularly surface dielectric barrier discharge (DBD), can be a good candidate for such purpose. The present experimental study focuses on optical and electrical characterization of plasma sheet formed by applying a pulse of voltage with rising and falling periods of 50 ns for a typical surface DBD geometry. Positive and negative polarities are compared in terms of current behavior, deposited energy, fast-imaging of the plasma propagation, and resulting modifications of the surrounding medium by using shadowgraphy acquisitions. Positive and negative pulses of voltage produce streamers and corona type plasma, respectively. Both of them result in the production of a localized pressure wave propagating in the air with a speed maintained at 343 m/s (measurements at room temperature of 20 °C). This suggests that the produced pressure wave can be considered as a propagating sound wave. The intensity of the pressure wave is directly connected to the dissipated energy at the dielectric wall with a linear increase with the applied voltage amplitude and a strong dependence toward the rising time. At constant voltage amplitude, the pressure wave is reinforced by using a positive pulse. The present investigation also reveals that rising and decaying periods of a single pulse of voltage result in two distinct pressure waves. As a result, superposition or successive pressure wave can be produced by adjusting the width of the pulse.

We confine the nanosecond repetitively pulsed discharge (NRP) to the micrometer scale, in a 200-µm discharge gap in air at atmospheric pressure and room temperature, focusing on measurements of the electron number density and electron temperature. The Stark broadening of H, O and N atomic lines and electrical conductivity both show that the electron number density reaches a maximum value of 1×10 19 cm -3 . Boltzmann plots show the electron temperature to be 72 kK several nanoseconds after the end of the pulse of applied electric field.We will use these results to determine the mechanism responsible for electron loss during the early recombination phase (t < 500 ns) and comment on the degree of ionization and dissociation.

Active flow control is a rapidly developing topic because the associated industrial applications are of immense importance, particularly for aeronautics. Among all the flow control methods, such as the use of mechanical flaps or wall jets, plasma-based devices are very promising devices. The main advantages of such systems are their robustness, their simplicity, their low-power consumption and that they allow a real-time control at high frequency. This paper deals with an experimental study about the electric wind produced by a surface discharge based on a three-electrode geometry. This new device is composed of a typical two-electrode surface barrier discharge excited by an AC high voltage, plus a third electrode at which a DC high voltage is applied in order to extend the discharge region and to accelerate the ion drift velocity. In the first part the electrical current of these different surface discharges is presented and discussed. This shows that the current behaviour depends on the DC component polarity. The second part is dedicated to analysing the electric wind characteristics through Schlieren visualizations and to measuring its time-averaged velocity with a Pitot tube sensor. The results show that an excitation of the electrodes with an AC voltage plus a positive DC component can significantly modify the topology of the electric wind produced by a single DBD. In practice, this DC component allows us to increase the value of the maximum induced velocity (up to +150% at a few centimetres downstream of the discharge) and the plasma extension, to enhance the depression occurring above the discharge region and to increase the discharge-induced mass flow rate (up to +100%), without increasing the electrical power consumption.

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