1996 , Volume 1, № 1, p.82-97

In recent years, as the problems related to environmental conservation of water area and coastal development have become more serious and more complicated, it has become important to clarify the characteristics of the various kinds of density currents. A density current is the flow of one fluid within another caused by the density difference between the two fluids.In this paper, we would like to report a curious self-oscillatory phenomenon, so called saline oscillator, induced by gravitational instability.An oscillatory flow is generated here, when a cup having small orifice in its base filled with saline water is placed within an outer vessel containing fresh water (Fig. 8). This system exhibits various nonlinear characteristics such as bifurcation of the oscillatory flow, oscillation cycle time and entrainment among the oscillations according to various experimental conditions.In order to explain the simple saline oscillatory phenomenon, numerical simulation in two dimensional system has been performed. We have developed a simulation program for incompressible fluids that is extended to calculate the two layer time-dependent density currents. In this simulation program, a low diffusion, stable and high-accurate algorithm called Cubic-Interpolated pseudo-Particle (CIP) method for solving hyperbolic equations was adopted to calculate the Navier-Stokes equation and the equation of mass conservation.The experimental trend on the behavior of oscillatory flow has been reproduced in this simulation in a qualitative manner. The comparison between the results of its computation and experiment is fairly good (Fig. 9).

*65D05 Interpolation

65N06 Finite difference methods

76D05 Navier-Stokes equations

*G.1.1 Interpolation

G.1.8 Partial Differential Equations

J.2 Physical Sciences and Engineering (Computer Applications)