No abstract

Nanosecond-pulse electrical discharges offer an efficient means of plasma generation in applications, but accurate numerical simulation of these discharges remains extremely challenging. The continuing difficulties lie in an enormous separation of space and time scales, a lack of transport and kinetic data, and extreme nonequilibrium physics. In the face of these challenges, we present an example of good practice in selecting the physical model and comprehensively checking numerical accuracy. We focus on a particular discharge experiment, and illustrate how simulations can provide useful guidance for ongoing experimental work, despite the difficulty of the simulations. The target experiments were carried out in a planeto-plane electrode configuration with a 20 mm gap in 400 Pa (3 Torr) argon using 3 ns, 850 V pulses with a 30 kHz pulse repetition frequency. The model employed the drift-diffusion approximation for species motion, and the self-consistent electric field was obtained through the solution of the Poisson equation. The baseline physical model utilized the local field approximation. In an extended model, non-local-field effects on the electron temperature were investigated by solving a simplified electron energy equation. Calculations were carried out for both a pure argon kinetic model and an argon-water model. The model generally underestimated the measured electron number densities, but the inclusion of additional physical effects helped to reduce the discrepancy with experiment. These results represent a step toward efficient modeling of pulsed electrical discharges for applications to combustion enhancement, flow control, and plasma antennas.

The main purpose of this study is to analyze hypersonic flow field around the blunt bodies and to design of that bodies in order to obtain minimum pressure drag. Modeling of non-equilibrium must be done properly. In this study, non-equilibriums of thermal and chemical modes are considered. Translational and rotational energy modes are assumed that energy exchange between these modes is so fast. Vibrational and electronic energy terms are neglected. Therefore, one temperature is used to model thermo-chemical non-equilibrium. Flow field is assumed as inviscid and continuum region. Moreover, there is not diffusion. Thus, to model chemical non-equilibrium, finite rate chemistry can be used. For the thermal-nonequilibrium, enthalpy, entropy and specific heat constants are obtained from curve fitting methods. The coupled flow field equations are solved by using Newton's methods. To solve Newton's method, Jacobian matrices evaluation is required. In terms of convergence, Jacobian matrices are obtained by using analytical methods. At the design part, sensitivities are obtained by using adjoint design methods. The aim of design part is finding a hypersonic blunt geometry with minimum pressure drag while keeping the maximum temperature smaller than the baseline value. Nomenclature w flow variable vector in computational domain F, G flux vectors H, S source vector R residual in computational domain P static pressure of mixture P e electron pressure E total energy per unit mass H total enthalpy per unit mass h s mixture enthalpy per unit mass E v mixture vibrational-electronic energy per unit mass J coordinate transformation Jacobian e v vibrational-electronic mass e sf source term of electron  , curvilinear coordinates s  species density s  mass production rate of chemical reactions , ij  viscous shear stress 1 Graduated Students, Aeronautical and Astronatical Engineering, tugba.piskin@metu.edu.tr , AIAA Member 2 Associated Professor, Aeronautical and Astronatical Engineering, seyi@metu.edu.tr, AIAA Member Downloaded by UNIVERSITY OF NEW SOUTH WALES on August 13, 2015 | http://arc.aiaa.org |

No abstract

No abstract