Plasma-induced Forces Research Articles

Plasma flow control simulations of a low-Reynolds number low-aspect-ratio wing

Large-eddy simulation (LES) is employed to investigate use of plasma-based control in order to improve aerodynamic performance of a flat-plate wing. The wing has a rectangular planform, a thickness to chord ratio of 0.016, and an aspect ratio of 2.0. Computations are carried out at a chord-based Reynolds number of 20,000, such that the configuration and flow conditions are typical of those commonly utilized in micro air vehicle (MAV) applications. Solutions are obtained to the Navier–Stokes equations, that were augmented by source terms used to represent body forces imparted by plasma actuators on the fluid. A simple phenomenological model provided these body forces resulting from the electric field generated by the plasma. The numerical method is based upon a high-fidelity time-implicit scheme and an implicit LES approach, which are applied to obtain solutions on an overset mesh system. The control strategy explores plasma actuators that are distributed in the spanwise direction along the wing leading edge, and actuators extending in the chordwise direction along the wing tip. The investigation considers plasma-induced forces that are imposed in either the co-flowing or counter-flow directions for the former arrangement, and directed inboard or outboard for the latter. Both continuous and pulsed operation of actuators are simulated, and the magnitude of the plasma force is varied in order to establish the most efficient means of control. Computations are carried out at angles of attack that are below (8.0deg) and above (25.0deg) the stall value. Control solutions are compared with baseline results without actuation to determine the most beneficial control strategies. It was found that actuation is effective only for sufficiently large values of the plasma force. A favorable comparison is shown with the limited available experimental data.

Numerical Study on Plasma-Based Control of Flow over a Square Cylinder

Over the past decade, a lot of attention has been paid to plasma actuators because they are useful tools for flow control. Previous successes with plasma actuators include drag and noise reductions from a circular cylinder, one of representative bluff bodies, mainly through separation delay. However, to the best of authors’ knowledge, no attempt has been made to examine its capability to control square cylinder wake with fixed separation points. The purpose of this study is to numerically investigate whether or not the square cylinder wake can be controlled by means of plasma actuators. In particular, a linear plasma synthetic jet actuator is adopted and attached to the rear side of the cylinder. In this study, we use an immersed boundary method combined with an empirical plasma model for plasma-based flow control. The present method is second order accurate in time and space. Results show that the wake behind the square cylinder can be controlled effectively when the plasma-induced force is strong enough. With the plasma actuator on, the mean drag is reduced and the Karman vortex shedding is alleviated because the induced jet increases the base pressure and prevents the separating shear layers from interacting with each other.

Particle transport modelling in semiconductor process environments

We review our recent efforts to develop and apply computational models that can predict fluid, thermal and particle transport in semiconductor process equipment such as that used for chemical vapour deposition or plasma etching. The purpose of this work is to supply equipment designers and operators with models that allow them to optimize process conditions and to develop tool designs that reduce particle contamination levels. The algorithms for predicting particle transport are briefly described. A Lagrangian approach is used in this work when both particle inertia and applied forces are important, while a Eulerian approach is used when both particle Brownian motion and applied forces are important. As an example, a commercial finite-element code is used to calculate the fluid and thermal fields in a simple geometry representative of real single-wafer processing tools, namely axisymmetric flow between a showerhead and a parallel plate separated by a small gap. Using the calculated velocity field, both Lagrangian and Eulerian particle transport formulations give the same particle collection efficiency for terminal-velocity-dominated deposition when particle inertia can be neglected. Although plasma-induced forces on the particles are not treated in detail, we discuss how models for these forces can be incorporated into the Lagrangian and Eulerian framework as they become available.