The circular hydraulic jump in low gravity

Abstract

An experimental study of the circular hydraulic jump (CHJ) was carried out to show how reducing gravity to 10^–2 times that of the Earth's normal gravity affects the CHJ diameter and the downstream flow patterns. Water was the working fluid. Measurements of the CHJ diameter and the shape of the free liquid surface across the jump were made in low gravity using the downstream fluid height and the flow rate as the parameters. Comparisons are made with normal–gravity flow conditions. A drop tower was used to create low gravity. The measurements are compared with an existing theory for predicting how gravity affects the CHJ diameter. Results show that the steady–state CHJ diameter is larger at low gravity than normal gravity. As the downstream fluid height is increased, the CHJ diameter at normal gravity moves inward, but at low gravity the CHJ diameter does not show a similar influence of downstream fluid height. The curvature across the CHJ is higher at normal gravity than at low gravity and the length of the transition zone from the upstream to downstream height increases as gravity is reduced. Waves in the downstream flow are observed for all low–gravity flow conditions but at normal gravity they were observed only for selected flow conditions, suggesting that the influence of surface tension and viscosity dominate at low gravity. Measured normal–gravity and low–gravity CHJ diameters were bounded by theoretical predictions which assume either fully developed or developing flow conditions for the upstream thin film.