Computational modeling of glow discharge -induced fluid dynamics
Glow discharge at atmospheric pressure using a dielectric barrier discharge can induce fluid flow and operate as an actuator for flow control. The largely isothermal surface plasma generation realized above can modify the near-wall flow structure by means of Lorentzian collisions between the ionized fluid and the neutral fluid. Such an actuator has advantages of no moving parts, performance at atmospheric conditions and devising complex control strategies through the applied voltage. However, the mechanism of the momentum coupling between the plasma and the fluid flow is not yet adequately understood. In the present work, a modeling framework is presented to simulate athermal, non-equilibrium plasma discharges in conjunction with low Mach number fluid dynamics at atmospheric pressure. The plasma and fluid species are treated as a two-fluid system exhibiting a few decades of length and time scales. The effect of the plasma dynamics on the fluid dynamics is devised via a body force treatment in the Navier-Stokes equations. Two different approaches of different degrees of fidelity are presented for modeling the plasma dynamics. The first approach, a phenomenological model, is based on a linearized force distribution approximating the discharge structure, and utilizing experimental guidance to deduce the empirical constants.
A high fidelity approach is to model the plasma dynamics in a self-consistent manner using a first principle-based hydrodynamic plasma model. The atmospheric pressure regime of interest here enables us to employ local equilibrium assumptions, signifying efficient collisional energy exchange as against thermal heating from inelastic collision processes. The time scale ratios between convection, diffusion, and reaction/ionization mechanisms are O(107), making the system computationally stiff. To handle the stiffness, a sequential finite-volume operator-splitting algorithm capable of conserving space charge is developed; the approach can handle time-step sizes in the range of the slowest species convection time-scale. The Navier-Stokes equations representing the fluid dynamics are solved using a well-established pressure-based algorithm. A one-dimensional two-species plasma model was employed as a test case for validation purposes. The momentum coupling is primarily caused by the combination of factors which include discharge chemistry, individual species transport properties, geometric construction and the nature of the insulator and electrode material. Overall, the paraelectric momentum coupling mechanism is due to the cumulative effect over time of the force field in the domain, as seen from our computations.
Parametric studies conducted on the operating variables such as voltage. Frequency and geometric arrangements indicated strong agreement with the observed experimental work. The applied voltage indicated a power-law dependence on the voltage for the measured force in the domain.
0538: Aerospace materials