EFFECT OF BOTTOM WALL FRICTION ON THE TRANSITION OF DEVELOPMENTAL STAGES OF GRAVITY CURRENT

Abstract

In experiments of locked-exchange flow, the flow structure at the head of the gravity current was examined. In a rectangular channel, a finite volume of fluid was instantaneously released into another fluid of slightly different density. By comparing the effect of the bottom shape, how the bottom wall friction influences transition to the stage of the developing gravity current was investigated. The movement of the position of the head of the gravity current was visualized by a digital video camera. As a result, it was found that when no disturbance from behind came to the head during the viscous stage, the front decelerated with the time to the power of 1/2 even in the case of existence of effect of bottom wall. The transition time from the initial stage to the viscous stage was shown to vary with the Reynolds number even in the change of shape in the bottom. The three-dimensional instability of the flow contributed to the mixing process through the head and the density interfaced behind it, which also affected the head velocity.