A new method to enhance the circulation of a enclosed bay by using small pillars set at the bay mouth is proposed. The method controls the strength of vortices that are generated at the bay mouth. Setting triangle shape of pillars by the side of the bay mouth, the vortices can be strengthen. Consequently, the circulation inside the bay grows large because the strengthened vortices move towards the head of the bay. In this study, the property of this method were investigated by surface flow data which were obtained by PTV analysis. A numerical simulation shows good agreement with the measurement data. The mechanism to generate vortices by pillars is also discussed with the result of the numerical simulation.

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Although the wind-induced flow is one of the dominant factors for the flow system in an enclosed basin, the most of the previous studies with numerical simulation have simply assumed the wind stress acting on the water surface to be uniform both in time and space. To elucidate the significance of these non-uniformity of wind stress, in the present study, a series of numerical experiments have been conducted for the flow in a rectangular enclosed basin under time-varying wind stress. The computational results show that there arises multi-cell flow structure in the mean flow pattern and the characteristics of the circulation system depend on the wind-fluctuation period relative to the natural period of the basin and the time required for establishing the circulation in the basin.

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PTV (Particle Tracking Velocimetry) is used to investigate the turbulence structure in a narrow rectangular open channel. Instantaneous velocity fields are measured by a visualization technique. As the result, spatial distribution of the two-dimensional divergence and the vorticity are also shown. It is recognized that the mutual relationship among these quantities of the time-averaged distribution is strongly affected by the secondary-flow in an outer region of the transverse cross-section in the channel.

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