The structure of a vortex ring in deformation process were investigated by means of smoke visualization technique. The photographs of the flow pattern of a section perpendicular to the axis of a vortex ring were taken continuously with a high-speed video camera. The solid picture of a vortex ring was obtained by constructing these photographs with a computer graphics tool. Just after generating a vortex ring, the solid picture displayed a shape like the doughnut. The circumferential distortion appeared regularly on the surface of a solid picture as the vortex ring travelled downstream and the solid picture grew into the polygon. The distortion of the inner side on the circumferential surface of the solid picture was larger than that of the outer side on the surface. At final stage, i.e., just before collapse of the vortex ring, it seemed that some pair of rings might enclose the vortex core of vortex ring. These pair of rings were not combined with the vortex core. The pair of rings may be constructed of a small pair of vortex ring which are generated due to the centrifugal instability.

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The natural convection in a horizontal particle layer underlying a fluid layer was observed. Polystyrene beads were used for the particle layer, which were laid in a tank filled with water. Convection pattern was visualized by the use of the microcapsule of the thermosensitivity liquid crystal and food dye. The fluid layer showed unsteady convection pattern. In the particle layer, two patterns of convection were observed. One was a convection of steady flow and linear in vertical distribution of temperature, the other was concentrated upward flow and curvilinear in vertical distribution of temperature.

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Transition to unsteady thermal convection in a square channel heated from below is predicted by means of the secondary instability analysis. In the presence of a through flow, longitudinal rolls are realized for the Reynolds number and the Rayleigh number above the critical values. They are two-dimensional steady convection rolls aligned along the channel. Stability boundaries of the longitudinal rolls with respect to three-dimensional infinitesimal disturbances are specified numerically for the Prandtl number Pr = 0.71. The longitudinal rolls are predicted to become unsteady three-dimensional convections as a result of three kinds of instabilities.

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Plume structure of open water deep convection is investigated by using a nonhydrostatic numerical model, with 157 experiments for different sets of physical parameters, which are Coriolis parameter, diffusivity, and surface buoyancy flux. A separation curve between two dimensional (2-D) and three dimensional (3-D) convection regimes is estimated with a higher accuracy than previously examined in a 2-dimensional parameter space of the natural Rossby number and flux Rayleigh number.
For the 2-D and 3-D regime transition, the validity of the hypothesis of maximum entropy increase rate is examined. At the 2-D and 3-D separation curve, entropy increase rates tend to change their gradient in a consistent manner with the hypothesis. This suggests a possibility that the regime transition of plume behavior is understood from a view point of macroscopic thermodynamics for a dissipative system.
In the 2-D regime, some experiments exhibited interesting vorticity structures, which are different from conventional heton structure. Three-dimensional visualization of iso-surface of vorticities indicated that vortex structure for these experiments is characterized a mushroom-like shape with a vital temporal variability or tube-like shape. These results indicate that the heton structures do not explain all of plume structures in the 2-D regime.

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