EHD INSTABILITY OF AIR LIQUID 2-LAYER SYSTEM UNDER UNIPOLAR CHARGE INJECTION/

We examine the hydrodynamic instability of a layer of insulating liqui d lying below a layer of air with free surface, the system being subje cted to a unipolar injection. It is shown first that there is no surfa ce charge at the air/liquid interface. A simple analysis of the static instability is developed which leads to a criterion in the two cases of weak and very strong injections in air. The usual convective instab ility of the insulating liquid layer is then analysed taking into acco unt the slight deformation of the interface.