Ehd propulsion

Modeling of an EHD corona flow in nitrogen gas using an asymmetric capacitor for propulsion
Alexandre A. Martins Institute for Plasmas and Nuclear Fusion & Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal Mario J. Pinheiro Department of Physics and Institute for Plasmas and Nuclear Fusion, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal

Abstract
The present work intends to identify the nature of the propulsive force that occurs during a positive corona discharge in nitrogen gas using an asymmetric capacitor geometry. We are going to apply the known theory of electrohydrodynamics (EHD) and electrostatics in order to compute all hydrodynamic and electrostatic forces that act on the considered geometry in an attempt to provide a physical insight on the force mechanism that acts on an asymmetrical capacitor.

Introduction
In this work we investigate the physical origin of the propulsion observed in an asymmetric capacitor that generates an electrohydrodynamic (EHD) flow through a corona discharge in nitrogen gas, at atmospheric pressure. The structure to be studied, an asymmetric capacitor, is represented in figure 1. The notation used for the electrodes is related to their respective radius of curvature. The positive corona wire has a much smaller radius of curvature r than the facing ground electrode R.
Positive Electrode R r Nitrogen G L Ground Electrode

Figure 1. Asymmetric capacitor with an air gap G, corona wire r and ground electrode R of length L.

Zhao and Adamiak (2005a, 2006) have studied such geometry with preliminary simulations performed using Fluent and their own code. They attribute the force mechanism mainly to electrostatic forces in the corona wire, directed away from the ground electrode, and state that there are no electrostatic forces on the ground electrode. We disagree with their results since, according to our study, the force on the corona wire has the opposite direction (is directed