UC Irvine

The Dielectric Barrier Discharge (DBD) plasma actuator is a commonly used flow control device. This device is capable of ionizing air using a high-frequency and high-voltage AC power source, creating positive ions and negative electrons. The ions travel in the direction of the external electric field, inducing a jet along the wall. This jet can delay the boundary layer separation, increase the lift-to-drag ratio, and suppress the fluctuations in the wake. The DBD plasma actuator has many advantages, such as ease of installation, fast-acting capabilities, and high energy efficiency. Additionally, it requires no moving mechanical parts, making it one of the most efficient active control methods. While numerous papers have studied the application of the plasma actuator, only a few have explored its fundamental physics and the detailed mechanisms responsible for its flow control effectiveness. This research is divided into two parts. The first part examines the fundamental physics behind the ionization process, investigating how plasma is created by the high-power and high-frequency AC power source. The second part delves into the fundamental physics of plasma control on flat plates and conical bodies. In this research, the plasma effect is simulated by a mathematical model and treated as a source term when coupled with the 2D Navier-Stokes equations. This model has some parameters that require calibration based on experimental results. The first case examines the plasma-induced flow field on a flat plate under duty-cycle control. In this scenario, a single DBD plasma actuator is installed on the surface of a flat plate. The air is initially quiescent and the flow field is solely induced by the plasma actuator. In this case, essential parameters are obtained for the plasma body force model through calibration with available experimental data, thereby providing a fully-developed model. The simplicity of this case makes it perfect for the calibration process. The second case examines the flow field around a square cylinder under plasma control, where a pair of DBD plasma actuators are installed on different parts of the square cylinder. The fully developed plasma model is integrated into the SIMPLE algorithm as a source term. During the simulation, the incoming flow velocity is always set to $1m/s$, and the flow fields at $Re=100$ and $Re=200$ are simulated under three different installation configurations. In the first configuration, a pair of plasma actuators is installed on the front surface of the cylinder, generating two induced jets moving away from each other. In the second configuration, one actuator is placed on the top while another one is installed on the bottom of the cylinder, inducing two jets in the stream wise direction. In the third configuration, a pair of plasma actuators is installed on the rear surface of the cylinder, with two jets moving toward each other. After detailed analysis, we found that the third configuration produces the best flow control results, completely suppressing lift fluctuations and significantly reducing the time-averaged drag coefficient when the plasma body force is strong enough. In the third case, the plasma effect is simulated using a self developed plasma body force model, while the flow field is simulated by solving the Reynolds-Averaged Navier-Stokes (RANS) Equations with the Spalart-Allmaras (SA) one-equation turbulence model. This case is divided into three steps. In the first step, a new plasma body force model tailored for circular surfaces is developed to replicate the experimental flow field around a circular cylinder. In the second step, the flow fields under different steady-state actuation signals are simulated and the results are analyzed in detail. In the third step, the flow fields under unsteady actuations with varying duty-cycle frequencies and duty-cycle ratios are simulated. For both steady and unsteady actuation, the simulation results are compared with available experimental data. In addition to the findings reported in Hui's 2022 experiment, the simulation results unveil three significant new discoveries. First, the friction force on the surface of the circular cylinder responds instantly to the plasma actuation signal, whereas the momentum of the flow within the measurement window exhibits a time delay. Second, the momentum in the cross-stream direction forms an arc-like shape during one duty-cycle period, while the momentum in the streamwise direction remains relatively constant. Third, the time-accurate momentum exhibits only one peak within a duty-cycle period, while the pressure and friction forces exhibit multiple peaks. Furthermore, the magnitude of the pressure force greatly surpasses that of the friction force.