In this paper, a curved class of plasma actuator geometries is presented. The intension of this paper is to extend the versatility of a dielectric barrier discharge plasma actuator by modifying the geometry of its electrodes, so that the plasma generated body force is able to excite a broader spectrum of flow physics than plasma actuators with a more standard geometry. Two examples of flow control are demonstrated numerically. An example of this class of actuators is shown to generate boundary layer streaks, which can be used to accelerate or delay the laminar to turbulent transition process, depending on how they are applied. Simulations of a low Reynolds number airfoil are also performed using additional examples of this class of actuators, where it is shown that this plasma actuator geometry is able to introduce energy into and excite a secondary instability mode and increase unsteady kinetic energy in the boundary layer. These two cases show that this general class of curved actuators possesses an increased versatility with respect to the standard geometry actuators. V

The response of a zero pressure gradient boundary layer modified by flow-wise oriented momentum injection similar to that of a plasma actuator is calculated using a two-dimensional (bi-global) stability analysis. It is found that the addition of momentum into the boundary layer has a significant impact on Tollmien-Schlichting waves, which may be damped by up to two orders of magnitude. Changes to the exponential growth rate of the perturbations are also measured. These stabilizing effects are largely due to the momentum addition modifying the downstream boundary layer profiles, but localized stabilization effects are also noted. The relative stabilization of the TS wave appears to be a linear function with respect to the ratio of the plasma-induced wall jet velocity under quiescent conditions and the free-stream velocity for lower levels of plasma actuation (i.e. velocity ratios less than 0.1). For higher levels of plasma actuation, the relative stabilization of the TS wave appears to be exponential with respect to the total momentum addition to the boundary layer by the plasma actuator.

A flow's transition from laminar to turbulent leads to increased levels of skin friction. In recent years, dielectric barrier discharge actuators have been shown to be able to delay the onset of turbulence in boundary layers. While the laminar to turbulent transition process can be initiated by several different instability mechanisms, so far, only stabilization of the Tollmien-Schlichting path to transition has received significant attention, leaving the stabilization of other transition paths using these actuators less explored. To fill that void, a bi-global stability analysis is used here to examine the stabilization of boundary layer streaks in a laminar boundary layer. These streaks, which are important to both transient and bypass instability mechanisms, are damped by the addition of a flow-wise oriented plasma body force to the boundary layer. Depending on the magnitude of the plasma actuation, this damping can be up to 25% of the perturbation's kinetic energy. The damping mechanism appears to be due to highly localized effects in the immediate vicinity of the body force, and when examined using a linearized Reynolds-averaged Navier-Stokes energy balance, indicate negative production of the perturbation's kinetic energy. Parametric studies of the stabilization have also been performed, varying the magnitude of the plasma actuator's body force and the spanwise wavenumber of the actuation. Based on these parametric studies, the damping of the boundary layer streaks appears to be linear with respect to the total amount of body force applied to the flow.

Experimental measurements and numerical simulations of a dielectric barrier discharge driven flow inside a finite length channel have been performed. Plasma actuators have been used to impart momentum to the flow in the near wall region, which diffuses throughout the height of the channel as it convects downstream. This momentum addition is found to be of sufficient magnitude to create an unsteady channel flow with exit velocities on the order of 1–3 m/s. Pressure and velocity measurements have been taken in order to quantify the effects of varying the number of symmetrically placed pairs of plasma actuators in the channel and the operating voltage applied to the actuators, showing a monotonic increase with respect to both parameters. Power law relationships have been determined for these measurements with respect to the operating voltage, with exponents of 2.0 for the exit velocity and of 5.6 for the maximum pressure differential. The pressure measurements also suggest that the pressure increase due to each actuator is independent of the bulk flow inside the channel. Numerical predictions also agree with the measured pressure and velocity distributions across the channel. The bulk velocity and pressure measurements allow for efficiency calculations of the plasma channel, which are shown to also fit into a power law relationship with respect to the operating voltage. The data collected show that the efficiency of these devices is low, less than 0.1%, but that it increases with a power law exponent of 4.09 to 4.35 indicating the possibility of using such channel for pumping small flows.

The short term transient and long term periodic unsteady effects of pulsed plasma actuation are studied using an unsteady, compressible Navier-Stokes solver for the case of a partially separated transitional flow over an SD7003 airfoil at 4º angle of attack and at Re=40,000. Forcing magnitude and its effect on the flow field is examined. Distinctly different behavior is observed parameters are adjusted. The unsteady simulations show that the actuators have a quick transient response, reattaching the separated flow within 2 nondimensionalized units of time, but nearly independently of the forcing magnitude. Spikes in C l , C d , and C m are observed during reattachment, most likely due to vortex pairing at the trailing edge.