Electrohydrodynamics (EHD), is the academic discipline which studies the dynamics of electrically-conducting fluids. It is the study of the motions of ionised particles or molecules and their interactions with electric fields and the surrounding fluid. The term may be considered to be synonymous with the rather elaborate electrostrictive hydrodynamics. In general, the phenomena relate to the conversion of electrical energy into kinetic energy, and vice versa.
In the first instance, shaped electrostatic fields create hydrostatic pressure (or motion) in dielectric media. When such media are fluids, a flow is produced. If the dielectric is a vacuum or a solid, no flow is produced. Such flow can be directed against the electrodes, generally to move the electrodes. In such case, the moving structure acts as a motor. Practical examples of EHD are the common air ioniser and EHD thrusters.
In the second instance, the converse takes place. A powered flow of medium within a shaped electrostatic field adds energy to the system which is picked up as a potential difference by electrodes. In such case, the structure acts as a generator.