This report provides a brief overview of ocean currents and their measurements. In particular, some results are reported of recent moored and acoustic measurements of the Kuroshio.

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Selection of optimum sets and kinds of damping screens for a low turbulence wind tunnel settling chamber is investigated. Existing low turbulence wind tunnel settling chamber is used as test section preparing hot wire traversing holes after rapid expansion diffuser, honeycomb, and ten screens. Hot wire anemometer with temperature compensation circuit is used for measuring the velocity profiles and turbulence intensity levels inside the settling chamber and working section of the tunnel. The results show that the number of screens determined by classical method is not appropriate when the number increase more than about five. Turbulence level produced by a damping screen itself becomes important when the turbulence level of on-coming flow is already low enough (less than 1%). It is also found out that the distance needed for the natural damping of the turbulence level after the final screen becomes very important for a low turbulence wind tunnel.

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A numerical procedure to solve unsteady natural convection flow problems is presented. The governing equations in primitive variables are made non-dimensional to a well balanced form and transformed into generalized coordinates to treat flow problems with a wide range of parameters and complex geometry. The solution procedure of finite difference is applied in such a way that the viscous terms are calculated by central differences and the convective terms by the Generalized QUICK method. The time integration is performed by a two-step method with the second order accuracy to give a proper solution at every time step. The pressure is obtained by solving the Poisson equation with a modified source, which improves the convergence of iterations. As a key point in this study, pressure boundary conditions and pressure distributions are carefully investigated. The natural convection flow in a square cavity heated below is selected as a test problem. Three cases were calculated : Pr=0.72, 10 and 100 for Gr=10⁶, where a steady solution for Pr=0.72 and unsteady solutions for Pr=10 and 100 were obtained.

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The effective length of a hot-wire sensor of an anemometer is shown to be shorter than its geometrical length by a factor around 2/3 if the nondimensionalized length is of order 3. This is due to the fact that the end regions of a hot-wire are not very sensitive to the wind speed. The analytic expression for the temperature distribution over a finite length hot-wire immersed across two regions of different wind-speed is numerically integrated and differentiated, to give the local wind-sensitivity of the wire. Then, assuming a sinusoidal distribution with the maximum at the center of the hot-wire for the spatial distribution of a velocity fluctuation, the sensitivity of the hot-wire as a whole to such a velocity fluctuation is calculated, giving the above referred results.

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The behavior of vortex streets at density interfaces in stratified shear flows is investigated using a linear theory. Secondary vorticity is generated at the surface of the vortex by the difference between directions of the density gradient and the gravitational acceleration. Newly generated circulation is estimated by integrating secondary vorticity over the surface of the vortex.

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