PIV and shadowgraph measurements of thermo-electrohydrodynamic convection in a horizontal aligned differentially heated annulus at different gravity conditions

Abstract Convection of a dielectric fluid confined in a differentially heated annulus with an inhomogeneous radial electric field is investigated under different gravity conditions. The annulus axis is aligned horizontally such that the so called “crescent shape pattern” of two axisymmetric convection cells develop when gravity is present. To apply different gravity conditions the experiment is placed in an aeroplane that is capable to produce gravity levels between ~ 10 - 2 g to ~ 1.8 g . The experimental parameter range investigates natural convection during the varying gravity phases and thermo-electrohydrodynamic (TEHD) convection in microgravity. The recorded PIV and shadowgraph images provide a better understanding towards pre-existing literature e.g. where natural convection is more intense during hypergravity, the onset of the TEHD-convection in microgravity and the transition between both convective states. Results of the experiment reveal an insight of the helicoidal nature of the TEHD-instability in a microgravity environment which corresponds to previous literature. Nevertheless, differences may arise and could refer to the intrinsic time scale to let the pre-existing natural convection dissipate in the short transition time of the different gravity phases.