Ionic windIonic wind refers to the air motion produced by drifting charges, accelerated by an electric field whilst colliding with neutral air molecules. These collisions transfer part of the ions momentum into the air in the direction of the applied electric field, so that a macroscopic wind is created, the so-called ‘ionic-wind’. This wind is related to Electro-Hydro-Dynamic (EHD) propulsion since it produces air motion from the action of an electric field into the air. Since specific effects associated with charge creation arising in gases only are needed for ionic wind to arise, the less common acronym Electro-Aero-dynamic (EAD) is also used in the community.
Ionic wind is of interest in distinct applications such as electrostatic precipitators, gas and ionic pumps, miniaturized heat-cooler, xerography (i.e. electro-photography) and propulsion. In gases, charge creation are generally associated with the existence of a corona discharge, which is a cold plasma near a high electric field.
propulsion is an emerging field of investigation in the context of air-plane electrification and low-carbon air transportation. Recent advances in the field by Pr. Barrett team at MIT have demonstrated the (short) autonomous flight of a 3m span drone, partly motivated by our previous prediction that gliders such as Solar Impulse II could be propelled, in stationary flight, by ionic wind. In this emerging field, active investigations are in progress in various directions, including trying to improve ion-sources reliability and operability, (e.g. for drone propulsion applications).
What can we learn about the propulsive capabilities of ionic wind and the underlying physics by conjugating experimental investigations, numerical modeling, and theoretical analysis?
During the last years we experimentally confirmed (as other groups) the original findings of Pr. Barrett group that ionic wind provides a much larger thrust-to-power ratio than classical thermal engines, allowing the stationary flight of gliders such as Solar Impulse II (see Monrolin et al, 2017). We also confirmed the existence of optimal source configurations (
emitters/collectorsThese high electric fields are generated by high voltage sources called emitters in the vicinity of which charges are created. Among those charges, unipolar charges are migrating from the emitter vicinity, out of the narrow corona-discharge region, into air, toward the electrode of opposed polarity, which is called a collector since it collects the charges.
) for ionic wind propulsion and we understood, from Particle Image Velocity (PIV) experimental analysis, that this optimality is associated with a trade-off between maximizing the electric field and lowering the drag force (see Monrolin, 2018). We also recently demonstrated that the observed thrust can be predicted by numerical simulations in many configurations (see Coseru et al, 2021). From a more fundamental viewpoint we also progressed on the understanding of the corona discharge physics which, being the origin of charges, is a central issue to ionic wind propulsion. First considering the simplest case of axi-symmetric electrode configurations, we performed a theoretical analysis which permits to (asymptotically) demonstrate Kaptzov hypothesis and Peek’s law, two well-known features of corona discharge (see Monrolin et al, 2018). We recently generalised this theoretical multi-scale asymptotic approach for general configurations so as to set up a rigorous framework for already used multi-domain formulation of corona discharge modeling (see Monrolin et al, 2019).
In the future we will focus on ionic wind propulsive capability in the presence of adverse flow, i.e. referring to airplane cruise velocity conditions. This question is challenging from experimental and theoretical/numeral aspects.
Flying with ionic windAn aeroplane can sustain steady-level flight using ionic wind.See Plouraboué, 2018Electrohydrodynamic thrust for in atmosphere propulsionExperimental thrust measurement.See Monrolin et al, 2017Electrohydrodynamic ionic wind, force ﬁeld, and ionic mobilityKinetic to electric power ratio versus collector spacing angleSee Monrolin, 2018Ion density, isopotential lines and electric field for 2 Emitters/2 Collectors configuration
Numerical study of Electro Aero dynamic force and current resulting from ionic wind in emitter/collector systems
Coseru et al, 2021Revisiting the positive DC corona discharge theory beyond Peek and Townsend lawCoaxial electrode geometry, asymptotic regions and the corresponding physical processes: (1) Primary electron avalanche, (2) secondary ionization,
(3) secondary electron avalanche, (4) ion drift.See Monrolin et al, 2018
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Flying with ionic wind Journal Article
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Electrohydrodynamic thrust for in-atmosphere propulsion Journal Article
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Innovative aerospace propulsion techniques: participation in a French public radio broadcast