Active Control of a Backward Facing Step Flow With Plasma Actuators

Active control over a backward facing step flow is studied experimentally by means of plasma based devices. The Reynolds number based on the step height h is 1520. An electrohydrodynamic actuator (EHD), dielectric barrier discharge (DBD) type, is flush mounted to the step wall. The DBD configuration adds momentum locally, normal to the separated shear layer, thus producing strong modifications downstream. The actuation is periodic and its frequency and amplitude are scrutinized to characterize the flow behavior under forcing. Measures of velocity fields for these flows are obtained from particle image velocimetry (PIV). As reported by previous works, the reattachment length shows an important reduction for an optimum forcing frequency. This value closely matches the shear layer flow natural frequency. On the other hand, the flow is less sensitive to the forcing amplitude though the analysis allows us to optimize the actuation in order to save power consumption.

Numerical investigation of electrohydrodynamic effects on the airflow through corrugated channels

To enhance the forced convection heat transfer of turbulent air stream inside the different corrugated channels, a numerical study has been conducted to explore the effect of electrohydrodynamic actuator. In this regard, a two-dimensional numerical approach has been developed to evaluate the average Nusselt number and friction factor. The results obtained show that, while the thermal enhancement factor without electrohydrodynamic is best with trapezoidal corrugation for flows in the low Reynolds number regime, the addition of electrohydrodynamic works best with rectangular corrugation.

DC and Pulsed Surface Corona Discharge along a Dielectric Flat Plate in Air: Electrical Properties and Discharge-Induced Ionic Wind

Several studies have shown that a surface corona discharge may be used as an electrohydrodynamic actuator in order to control the airflow around profiles. For a few years, our laboratory has been working on this subject, specifically in the case of a DC corona discharge. The present paper deals with experimental work on DC and pulsed surface non-thermal plasmas produced between two wire electrodes flush mounted on the surface of a PMMA (polymethyl-methacrylate) insulating flat plate. The goal is to optimize the plasma actuator in terms of electro-mechanical efficiency in the absence of an external free airstream. First, electrical properties (such as discharge current versus applied voltage and discharge current versus time) of these different discharges are observed. Secondly, the time-averaged ionic wind induced by DC coronas and pulsed coronas is measured by means of a small diameter tube connected to a micro manometer.

Influence of an Electrohydrodynamic Actuator on a Turbulent Boundary Layer Along a Flat Plate

For some years, the use of electrohydrodynamic actuators has been receiving special attention. These actuators have important advantages like simplicity, no moving part, a short electrical response time and a total electric control. The electrohydrodynamic actuator used here consists in two electrodes flush mounted on a flat plate, generating a corona discharge at close vicinity of the wall. Positive ions created at the anode move outside the immediate vicinity of the ionization zone and drift to the negative electrode. Momentum transfer as a result of collision between drifting ions and neutral air molecules gives rise to the electrohydrodynamic flow known as ionic wind. In this paper the ionic wind is used in order to modify the properties of a turbulent boundary layer. Profiles of the boundary layer are presented for velocity up to 25 m/s. They show the influence of the polarity of the discharge, resulting in a velocity decreasing or increasing. In the case of increasing velocity, they show an important drag reduction (30% at 10 m/s) and a boundary layer thickness reduction of about 20% at 10 m/s.

Control of the Airflow Close to a Flat Plate With Electrohydrodynamic Actuators

This work analyses the ability of an electrohydrodynamic actuator to modify the characteristics of a flow over a flat plate. The device considered uses flush mounted electrodes and a d.c. power supply to create a plasma sheet on the surface of the plate. We analyze the effect of this plasma sheet on the flow in the region close to the leading edge of the plate. From Particle Image Velocimetry and at incident flow velocities in the range 11.6–18.6 m/s, we estimate the force per unit surface exerted by the discharge. We conclude that it can induce an important acceleration of the flow close to the surface with a relative good efficiency when compared with other actuators.