重力流の先端部の3次元不安定性

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The three-dimensional instability of the head of gravity currents is investigated in the experiment and in the computation of lock-exchange flow. Visualization experiments were made with dye to observe the three-dimensional features of the head advancing along an open channel with rectangular section. The computational method for gravity currents developed in the previous paper was extended to the three-dimensional cases and applied to the lock-exchange flow problem. It is based on the finite volume solution of the incompressible Navier-Stokes equation for an inhomogeneous fluid and the transport equation for solute. Agreement between the experimental and computational results is good. The head subject to the three-dimensional instability forms a wavy frontline which consists of masses of heavy fluid going ahead as a mountain- valley structure. Each of the masses falls down laterally as well as forward, and therefore it spreads out in every direction to form an arc front. Some of them become large by running over adjacent masses. The enlarged masses suffer from the instability again, and then some smaller-scale mountains appear in that. As a result, the frontline of the current consists of boundaries of these masses of different scale, often superimposed on each other. This kind of three-dimensional instability also appears even in a non-dissipative case of free-slip boundary, which indicates that it is independent of the instability of the wall boundary layer. It is shown from the comparison with the two-dimensional computation that the three-dimensional flow structure possibly makes a significant contribution to the mixing process across the density interface behind the head and at the front, which may affect the speed of the head.
社団法人日本船舶海洋工学会の論文

重力流の先端部の3次元不安定性

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