Investigation of a Plasma Synthetic Jet Actuator for Flow Control

Among active flow control techniques, plasma synthetic jet (PSJ) actuators seem to be a promising technology to improve aircraft performances due to their short response time, high jet velocities and absence of moving parts. An electrical discharge is produced within a cavity, increasing pressure and temperature, causing the exhaust of the gas through the orifice. After few cycles a periodic behaviour is reached generating a plasma synthetic jet. A numerical and experimental investigation was conducted to characterize the performance of the actuator and its potential as an active flow control method. An original lumped-element physical model (LEM) able to predict the temporal evolution of the major thermo-fluid-dynamic quantities of the device was developed. The governing equations are fully gasdynamics based and include viscous losses; the air is modelled as a real gas and both radiative and convective heat transfer mechanisms are considered at walls. The correct simulation of the refill regime is guaranteed by the inertial term included in the unsteady Bernoulli's equation. Axisymmetric numerical computations, carried out with OpenFOAM computer code, has allowed one to calibrate the lumped model through the determination of some fitting parameters. Finally, experimental measurements have allowed the completion of device investigation, producing valuable information about pressure, jet velocity and duration of the discharge. Results for both single pulse mode and repetitive working regimes are obtained, providing insights on major actuation characteristics. High frequency oscillations in the time interval between two subsequent discharge pulses are observed and analytically justified resorting to the Helmholtz resonator model. A comparison between measurements and simulations is performed, showing a satisfactory matching of the data and demonstrating the validity of the LEM model in the prediction of a PSJ actuator behaviour.