Experiments on gravity currents down a ramp in unstratified and linearly stratified salt water environments

Abstract

Gravity current propagation in the stratified environment is one of key research topics in atmosphere and marine sciences, etc. A series of experiments were conducted to investigate lock-release gravity currents down a ramp into different ambient environments. The front velocity of gravity currents in constant-density ambient increases rapidly at first, then stays nearly constant; the front velocity in linearly stratification environments increases firstly but then decreases gradually. This development process can be divided into three stages, namely, acceleration stage, deceleration stage and separation stage. The flow can be characterized by the relative stratification S , the Reynolds number Re and the Richardson number Ri 0. The front location, the front velocity and the velocity profile were analyzed by high speed camera. A particle image velocimetry (PIV) technique was applied to study the velocity field and vorticity field. The result showed that the counterclockwise vortexes appearing at the upper boundary were mainly due to Kelvin-Helmholtz instability and the clockwise vortexes in the lower boundary arose from the viscous forces in the boundary layer. This paper revealed the dynamic characteristics of gravity currents in constant-density ambient and linearly stratification respectively. The result can be applied in situations such as salinity intrusion of estuary and submarine turbidity currents, etc.