Vincent Boucinha

Thermal Characterization of a DBD Plasma Actuator: Dielectric Temperature Measurements Using Infrared Thermography

Active flow control by plasma actuators is currentl y under investigation in order to improve the aerodynamic performance of vehicles. One of these actuators consists in using a surface dielectric barrier discharge (DBD) by creat ing a non-thermal plasma at the dielectric surface. The plasma discharge induces a low-velocity airflow, the so-called “ionic wind”, which can be used to modify external flows. In this study, we focus on the description of the thermal effect of a DBD actuator in order to contribute to a better understanding of the mechanisms of interaction with the flow. The te mperature of the dielectric surface was first determined with the plasma on and secondly af ter switching off the discharge. The measurements were conducted for several amplitudes and frequencies of the applied voltage. The study comprised two parts: in the first, measur ements were performed in quiescent air, and in the second, the influence of an external bou ndary layer over the discharge on the dielectric temperature was investigated.

Negative Spark Leaders on a Surface DBD Plasma Actuator

Plasma actuators are currently under investigations in order to improve the aerodynamic performances of vehicles. Such devices induce airflow of few kilometers per hour called ionic wind. A previous study showed that ionic wind velocity is limited by a particular regime of the discharge where bright and long sparks appear. In this paper, we present some typical images of these spark leaders.

Experimental Study of the Flow Induced by a Sinusoidal Dielectric Barrier Discharge Actuator and Its Effects on a Flat Plate Natural Boundary Layer

Since the mid-1990s, electrohydrodynamic actuators have been developed for modifying on subsonic airflows. The principle of plasma action is the use of the direct conversion of electrical energy into kinetic energy in order to act on the flow boundary layer. This paper presents our contribution to such an investigation concerning an electrohydrodynamic actuator consisting of several sinusoidal dielectric barrier discharges. First, the ionic wind induced by this actuator was measured with a pressure sensing probe. The induced flow velocity increased with the applied voltage and frequency. The particle image velocimetry system without external airflow showed the presence of induced swirls, generated by the ion movement in plasma. Then the action of this actuator on a flat plate boundary layer in parallel flow at zero incidence was studied in a subsonic wind tunnel. Experiments were performed for 15 m/s and 22 m/s. They showed that electric discharges (±8 kV, 1 kHz) acting on a laminar flow tripped the laminar-to-turbulent transition. Moreover, higher applied voltages (up to ±12 kV, 1 kHz) were necessary for modifying turbulent boundary layers.

Drag reduction of a 3D bluff body using plasma actuators

The aim of this study is to reduce the drag of a simplified car geometry using surface dielectric barrier discharge actuators. Experiments were conducted in a wind tunnel for a low Reynolds number (6.7.105) with the Ahmed body reference (rear slant angle of 25°, zero yaw angle). The effect of steady and unsteady actuation on the flow topology was investigated carrying out 2C-PIV and 1D hot wire measurements. The efficiency of the actuators was characterised by stationary balance measurements. Drag reductions up to 8% were obtained by suppressing the separation bubble above the rear window. The results suggest that plasma actuators are simple to implement on a model and can provide useful information for automotive aerodynamics through parametric studies with parameters relevant for flow control (position, surface, frequency and duty cycle of the pulsed actuation).

Study of a DBD plasma actuator dedicated to airflow separation control

Since about ten years, dielectric barrier discharge (DBD) was studied as electro-hydrodynamic (EHD) actuator for airflow control. A DBD surface discharge generates nonthermal plasma allowing to modify the boundary layer of airflow. The active control enables fast action on airflow. A thin flexible asymmetric DBD actuator was used in our study, each elementary DBD was made with two copper electrodes of 35 mum in thickness and 6 mm in width. Dielectric was a multilayer configuration using Kaptonreg and Mylarreg. Two lengths of electrode were used in applications mentioned below: 150 mm and 900 mm. The DBD actuator was characterized by means of electric and optical measurements: discharge currents, voltages and dissipated power of DBD actuator; spectroscopic measurements were also performed. All these measurements were done for several frequencies of power supply. For flow separation controls experiments, firstly, we performed tests on a 1 m length flat plate with an elliptic leading edge placed in an open wind tunnel. This wind tunnel has a test section of a 2 m times 0.5 m times 0.5 m (LtimesHtimesW). Several DBD actuators with 150 mm length electrodes were placed on the upper surface of the flat plate. The action of DBD actuator enables to obtain a more stable laminar boundary layer and to delay the laminar-turbulent transition. Secondly, a 1 m chord and 1.10 m span wing-like airfoil (BMVR130) was used to perform measurements. This airfoil was placed in a wind tunnel whose test section has dimensions of 5 m times 2 m times 2 m. DBD actuators with electrode length of 900 mm were installed on the extrados of profile every 30 mm from x/c = 0.02 to x/c = 0.8. However, only a few elementary DBDs (up to 4) operated simultaneously. The experiments were carried out for velocities up to 15 m/s (Re = 106) and for angles of attack ranging from 8deg to 16deg. Flow visualizations were performed with a PIV system, the drag and lift coefficients were deduced by aerodynamic balance measurements. At 10 m/s (Re = 670,000), the flow was fully reattached for the angles of attack from 8deg to 12deg. A lift increase of about 5% could be observed.