Pages 119-127
The effect of a vertical barrier on the behaviour of a gravity current in an open channel was investigated in the experiment and the computation. The unsteady density field during the interaction of the current with the barrier was measured by the digital image processing. The measurement system uses the property of the light transmitted through coloured water and absorbed at the increasing rate with the dye concentration. The digital images of the coloured water in two-dimensional motion taken with a digital video camera on the side of the tank were directly sent to the computer to convert the brightness to the concentration and to the density on every pixel in the frames. The computation was also performed in the same condition as the experiment to compare their results. The incompressible Navier-Stokes equation for an inhomogeneous fluid together with the transport equation for solute was solved by the finite volume method developed in the previous paper and modified in this paper to obtain a stable solution of the flow beyond the barrier. The results reveal the inner structure of the head of the current on impact. The heavy fluid runs up the vertical wall at the almost same speed as the advancing speed of the horizontal current on the bottom before the collision. The raised heavy fluid falls down along the wall so as to generate a solitary wave propagating back through the stratified layer left by the original current. The height to which the current runs up the wall and the time during which the elevation of the interface lasts are both affected by the traveled distance as well as the initial depth of the current, which indicates that the regime of the development of the current is one of the important factors that determine the behavior of the current meeting a barrier.
