Electroaerodynamic thrusters: Influence of a freestream on the current, ionic wind, and force produced by a DC corona discharge

In the past few decades, atmospheric plasma propulsion has sustained a growth of interest. Recent studies have demonstrated the feasibility of light air-breathing plasma-propelled aircraft near ground level. Typically, corona discharge actuators are employed. Yet, the effects of the freestream velocity on the discharge current, ionic wind, and thrust must be characterized. The present study focuses on a wire-to-cylinder and a wire-to-airfoil actuators in a wind tunnel in a co-flow configuration. Discharge current and PIV (particle image velocimetry) measurements were used to determine both the differences between the two collecting electrodes and the aforementioned effects of the freestream velocity. The measured current follows the modeling already reported in the literature with a linear increase of the current with the freestream velocity. Besides, an interaction occurs with the charge density between the electrodes, which strengthens the rise of the current with the velocity as the voltage increases. In the study, the charge density increases linearly with the voltage with a slope of 0.75 mC/m2/kV for both collectors. However, the airfoil collector results in a higher current than the cylinder at the same voltage. The local velocity increases in three main regions thanks to the ionic wind. With both actuators, a higher velocity was captured with actuation on the upper and lower surfaces of the collectors. With the cylinder, the interelectrode region experiences a notable rise in velocity as well. In all cases, the air velocity downstream of the actuators is increased by the actuation. The ionic wind is usually less than 1 m/s (around 0.3-0.5 m/s on average) and its effect on the incoming flow decreases when the velocity increases up to 10 m/s. The force was calculated in control volumes around the actuators. For both actuators, the electroaerodynamic (EAD) force is governed by the current, and at constant current, the same EAD force is obtained with the two collectors. Yet, the force decreases with the drag of the collector, leading to a cancellation of the thrust when the drag exceeds the EAD force. At the maximum current tested in the study, the cylinder collector cancels the thrust at around 3 m/s of freestream against 5 m/s with the airfoil, showing that this type of propulsion is currently only applicable to low-speed aircraft.