DYNAMIC EFFECTS OF THE HEAD EDGE BEHAVIOR OF GRAVITY CURRENT

Abstract

The flow of the gravity current plays an important role in the transportation and mixing of dis-solved or suspended nutrients and chemical substances. In this study, from the experiments and numerical simulations of locked-exchange flow, the flow structure at the head of the gravity current was investigated. In a rectangular channel, a finite volume of fluid was instantaneously released into another fluid of slightly different density. A comparison of theoretical methods, experiments and numerical simulations showed that the water depth and volume of the released fluid affected the velocity of the gravity current. In the initial stage, the head moved forward at a constant velocity and then decelerated. In the final stage, which was governed by viscosity, the front velocity decreased proportionally to the time to the power of 1/2 when the head was not disturbed from behind. Gravity current created a mass concentration at the head in the initial stage. As the mass concentration at the head decreased, the gravity current was slowed down by the viscous stage due to the effect of the bottom friction according to the theoretical analysis. In the viscous stage, the mass concentration at the head no longer existed. The transition stage from the initial stage to the viscous stage was shown to vary with the Reynolds number by the numerical simulation. Clarification of the behavior of the leading edge of gravity flow will help predict the formation of mass transport in oceans and lakes, contributing to the conservation of the aquatic environment.