Design, characterization, and scale-up of oscillating plasma actuators for turbulent drag reduction

In this article, we present the design of an array of plasma actuators (PAs) conceived to control turbulent wall-bounded flows and a unique characterization of its transient response. The actuator configuration is such as to induce a control flow oscillating along the spanwise direction aimed at reducing skin-friction in turbulent flows when tuned to the proper spatio-temporal scales. A full characterization of the transient behavior of the spatio-temporally evolving plasma discharges was carried out by high-speed Schlieren imaging, capturing up to 10,000 density/temperature gradient fields per second. From these images, the evolution of the plasma-induced flow was tracked with sub-millisecond temporal resolution and sub-millimeter spatial resolution, and the actuator performance was evaluated over a wide range of operating conditions. In addition to the characterization of the transient flow, several other relevant quantities were measured and reported: the average jet velocity, the electric power absorption, the plasma-OFF and plasma-ON PA capacitance, and the induced temperature of/from the considered plasma actuators/discharge. Finally, scaling arguments on actuator and power-electronics are presented and discussed as part of a design effort to install the array of oscillating plasma actuators in large-scale facilities able to reproduce flow regimes of interest for transport applications (e.g., aeronautical), such as the turbulent pipe flow facility in the CICLoPE laboratory.