Study on a Water Screen Formed by Vertical Buoyant Jet

Abstract

The diffusion problem of buoyant jets issuing vertically upwards into stagnant ambient fluid is treated. The jets are expected to be utilized as a fish screen to control fish behavior by fencing a water body with the buoyant jets. There have been many studies of vertical buoyant jets related to diffusion problems of warm water discharged from power plants. In these previous studies, the Gaussian error curve is assumed to give an adequate approxima-tion to the actual velocity and concentration distribution. However, our experiment shows that the instantaneous density distribution is discontinuous, but if the time mean is taken, the distribution is close to the Gaussian curve. On the basis of the results of this experiment, the problem of jets is developed theoretically by assuming the discontinuity of density on the boundary between jet and ambient fluid, which is verified by experiments.
The equations deduced to evaluate the entrainment of ambient fluid, velocity, and density are shown to be very simple in comparison with the usual equations, and have good accuracy for practical use.