28 th ICPIG, July 15-20, 2007, Prague, Czech Republi Plasma Discharges at Atmospheric Pressure for Boundary Layer Separation Control and Neutral Flow Propulsion Alexandre A. Martins 1 and Mario J. Pinheiro 2 1 Center for Plasma Physics, Instituto Superior Tecnico, 1049-001 Lisboa, Portugal 2 Department of Physics and Center for Plasma Physics, Instituto Superior Tecnico, 1049-001 Lisboa, Portugal Progress on the understanding of the mechanism of the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP TM ) is reported. Numerical modelling and developing an efficient method of ions acceleration through the dielectric surface could provide a new way to enhance gas speed on the boundary layer limit. We calculated the gas voltage, memory voltage, conduction and displacement current as a function of time, giving evidence of the successive streamers that occurs in this kind of dielectric barrier discharge. The populations of ionic species N 4 + , N 2 + , O 2 + , O 2 - and electrons are obtained by solving self-consistently the ions governing equations (solved with Patankar algorithm) coupled with Poisson equation, and the Boltzmann equation for electrons solved in the two-term approximation, respectively. The electric field, electric potential, electron temperature, body forces and gas speed are obtained. 1. Introduction There has been a growing interest in the field of plasma aerodynamics related to its outstanding importance in active flow control, overriding the use of mechanical flaps [1,2]. The plasma created above a blunt body was shown to modify the laminar- turbulent transition inside the boundary layer, to induce or reduce the fluid separation, reducing drag and avoiding unwanted vibrations or noise [1,2]. In this work, we continue our previous investigation [3] started by one of us (MJP) during a visit to the Plasma Laboratory of Prof. John R. Roth of the University of Tennessee, at Knoxville, USA. We characterize the main physical properties of a plasma accelerator device, the so called One Atmosphere Uniform Glow Discharge Plasma (OAUGDP TM ) [1]. This is a relatively simple RF device and has been proposed as a plasma actuator generating electrohydrodynamics (EHD) body forces, allowing boundary layer flow control [1]. It operates on displacements currents and gives rise to neutral gas flow acceleration mechanism. Actuators placed on the leading edge of an airfoil can control the boundary layer separation, while if located at the trailing edge can control lift [4]. Enloe et al. [5] have found experimentally that the thrust T and maximum induced speed u max are proportional to the input power P, which depends nonlinearly on the voltage drop V Δ across the dielectric: 2 / 7 max V P u T Δ ∝ ∝ ∝ (1) The net Coulomb force acting on the charged particles, the EHD force, is given by [1,6]: ( )E e n i n e F r r - = , (2) where n i and n e are the ion and electron number density. We present in this work a self-consistent 2-DIM modelling of the temporal and spatial development of the OAUGDP TM from a perspective of better understanding the underlying physical mechanisms of the plasma actuator. 2. Numerical model 2.1. Description The plasma actuator simulation domain is a 2-Dim Cartesian geometry with the total length along the Ox-axis L x =4 mm and height L y =4 mm. It consists of conductive copper strips (with negligible thickness) of width=1 mm, separated by a 0.065 cm thick dielectric with width=3 mm and relative dielectric permittivity 5 = r ε . The capacity of the reactor is given by the conventional formula d S r ds C ε ε 0 = . The working gas is a "airlike" mixture of a fixed fraction of nitrogen ([N 2 ]/N=.78) and oxygen ([O 2 ]/N=0.22), as is normally present at sea level at p=1 atm. The electron homogeneous Boltzmann equation is solved with the 2-term expansion in spherical harmonics for a mixture of N 2 -22 %-O 2 . Using the set of cross sections of excitation by electron impact taken from [7] rates coefficients and transport parameters are obtained. The chemistry is presented in Ref.[3] and the species included in the model are: N 4 + , N 2 + , O 2 + , O 2 - and electrons. At 1 atm the concentrations of N 4 + ions are bigger than N 2 + , due partially to the reaction N 2 + + N 2 → N 4 + , which occurs at a higher rate than the direct ionization. Remark that at atmospheric pressure the local