Analysis of plasma-based flow control mechanisms through large-eddy simulations

摘要

High-fidelity simulations will become ever more important in the future if their use is routinely extended beyond engineering prediction to scientific analysis of the underlying physics. In particular, carefully conducted simulations can provide insight into aspects that are difficult if not impossible to explore in experiments. In this paper, we highlight such use of CFD to understand plasma-based flow control techniques, with emphasis on how the disturbances couple to the flowfield for actuators that are heat (as opposed to force) based. We present results with a relatively new type of actuator, the Nano-Second Dielectric Barrier Discharge (NS-DBD), which is formed by a flush mounted and embedded electrode combination excited by sharp (0(50) ns) pulses. A numerical model is presented and then applied to explore control of a stalled NACA 0015 airfoil at 15° angle of attack. These new results are assimilated with prior efforts on Localized Arc Filament Plasma Actuators (LAFPAs), to examine the differences in response of free versus bounded shear layers. It is shown that the initial manifestation of the disturbance occurs in the form of weak streamwise vortices. At the low levels of excitation of interest in scalable application, pulsing is essential for amplification in both types of shear layers. Hairpin-like structures characteristic of entrainment are also a common feature. Differences are evident however due to the no-slip condition of the boundary layer, where multiple induced counter-rotating vortices are observed prior to breakdown.