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 mechanism of formation of this plasma sheet, which is shown to be similar to the streamer formation. We show flow visualizations at low flow velocities (≈1m/s) and results from Particle Image Velocimetry at higher flow velocities (range 11.0-17.5 m/s). These results show that the discharge can induce an important acceleration of the flow close to the surface.

International audienceWith this work, we propose improvements to the construction of low-order dynamical systems (LODS) for incompressible turbulent external flows. The model is constructed by means of a proper orthogonal decomposition (POD) basis extracted from experimental data. The POD modes are used to formulate an ordinary differential equation (ODE) system or a dynamical system which contains the main features of the flow. This is achieved by applying a Galerkin projection to the Navier-Stokes equations. Usually, the obtained LODS presents stability problems due to modes truncation and numerical uncertainties, specially when working on experimental data. We perform the model closure with a variational method, data assimilation, which refines the state variables within an iterative scheme. The technique allows as to correct the dynamic system coefficients and to identify and ameliorate the issued experimental data

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The wake of a circular cylinder performing rotary oscillations is studied using hydrodynamic tunnel experiments at Re=100. Two-dimensional particle image velocimetry on the midplane perpendicular to the axis of a cylinder is used to characterize the spatial development of the flow and its stability properties. The lock-in phenomenon that determines the boundaries between regions of the forcing parameter space where the wake is globally unstable or convectively unstable [see Thiria and Wesfreid, J. Fluids Struct. 25, 654 (2009) for a review] is scrutinized using the experimental data. A method based on the analysis of power density spectra of the flow allows us to give a detailed description of the forced wake, shedding light on the energy distribution in the different frequency components and in particular on a cascade-like mechanism evidenced for a high amplitude of the forcing oscillation. In addition, a calculation of the drag from the velocity field is performed, allowing us to relate the resulting force on the body to the wake properties.