Simulation of supersonic flow phenomena in the presence of direct-current surface plasma actuators

A computational study of the effects of surface direct-current glow discharge actuation on supersonic flows is presented. A Navier-Stokes solver is used to compute the supersonic flow and the plasma actuators are modeled using a phenomenological approach. The actuator of interest consists of two electrodes flush-mounted on a flat plate. In the absence of external magnetic fields, the principal actuation mechanisms are electrostatic forcing and volumetric gas heating. The Navier-Stokes solver uses finite-volume spatial discretization and is based on an unstructured grid framework. A dual-time stepping algorithm is used to generate time-dependent solutions. The plasma actuator model comprises a separate electrostatic forcing model and a volumetric heating model to represent the effect of the plasma on the flow. The electrostatic forcing model is based on Child's law for a collisional cathode sheath and the volumetric heating effect is modeled using an asymmetric Gaussian distribution. Two modes of the glow discharge are studied using the actuator model in the presence of supersonic flow: a low-power (diffuse) mode and a high-power (constricted0) mode. The effects of electrostatic forcing and volumetric gas heating are examined individually and in combination using surface and field plots of pressure and temperature. Results from computations indicate that the diffuse mode discharge results in a stronger perturbation to the flow compared to the constricted mode discharge, which is mainly attributed to the volumetric heating of the bulk flow. The effects of the position of the electrodes relative to the bulk supersonic flow (cathode upstream and cathode downstream) are studied using sensitivity parameters in the electrostatic forcing model. The results show that electrostatic forcing, despite being small in magnitude, plays a significant role in the flow actuation. The effect of inter-actuator distances and coupled effects between two actuators placed in series are also studied. The magnitude of the surface pressure rise increases as the inter-actuator distance is made smaller.