Corona Discharge in Wind for Electrically Isolated Electrodes

For various problems in atmospheric electricity it is necessary to understand the behavior of corona discharge in wind. Prior work considers grounded electrode systems, of relevance for earthed towers, trees, or windmills subjected to thunderstorms fields. In this configuration, the effect of wind is to remove the shielding ions from the coronating electrode vicinity strengthening the corona and increasing its current. There are a number of cases, such as isolated wind turbine blades or airborne vehicles, that are not completely represented by the available models and experiments. This paper focuses on electrode systems that are electrically isolated from their environment and reports on a wind tunnel campaign and accompanying theoretical work. In this configuration, there are two competing effects: the removal of the shielding ions by the wind, strengthening the corona; and the electrode system charging negatively (for positive corona) with respect to its environment, weakening the corona. This leads to three different operating regimes; namely, for positions that favor ion recapture, charging is limited and current increases with wind as in the classical scaling; for positions that favor ion transport by the wind, the system charges negatively and the current decreases with wind; for the later configuration, as wind increases, the current can vanish and the system potential saturates. The results from this work demonstrate that classical scaling laws of corona discharge in wind do not necessarily apply for isolated electrodes and illustrate the feasibility of using a glow corona in wind for controlled charging of a floating body.