[in Japanese]

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Laminar dispersion coefficients both in an elliptical pipe and a rectangular pipe have been studied theoretically. Change in laminar dispersion coefficient with respect to cross-sectional shape is discussed for a wide range of aspect ratio Ar.
Non-dimensional dispersion coefficient both in an elliptical pipe and a rectangular pipe attains the minimal value at Ar=1 and is logarithmically symmetrical about it. The behavior of non-dimensional dispersion coefficient for Ar≠1, however, is remarkably different between an elliptical pipe and a rectangular pipe : the former monotonously increasing with Ar→∞ and Ar→0, whereas the latter approaching an asymptotic value as Ar→∞ and Ar→0. The result suggests that material transport in an elliptical pipe flow with very large (or small) aspect ratio can not be described by the one-dimensional dispersion equation based on G. I. Taylor's hypothesis. At Ar=1, non-dimensional dispersion coefficient in a square pipe is greater than that in a circular pipe. Comparison of dispersion coefficient with different cross-sectional shapes reveals that geometrical shape of a pipe decidedly affects the change in laminar dispersion coefficient with the aspect ratio.

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The lift force acting on circular cylinders submerged in sinusoidally oscillating flows was studied in a water tunnel. The measurement of the lift force reveals that the frequency of the force fluctuation is locked in that of the oscillatory flow for broad band of the KC number. The lift coefficient is correlated with the KC number and the β number. The flow visualization made with fine polystyrene particles showed that the fluctuation of the lift force is correlated with the vortex shedding and decaying, and the variation of the lift force with time was reasonably reproduced from the vorticity field. The intermittency of the lift force, i. e. beat, was successfully explained in terms of the instability of the vortex shedding.

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Analysis is made for unsteady mixed convection induced by gravity around a sphere which is located in a vertical uniform stream and whose surface temperature is suddenly increased. Asymptotic solutions for small Reynolds number are obtained by using the method of matched asymptotic expansions. It is shown that the velocity is expressed in terms of four expansions reflecting the existence of four distinct regions in the (r, τ) plane, r and τ being a non-dimensional radial co-ordinate and the non-dimensional time respectively.

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A wind tunnel experiment has been made on the structure of turbulence in a thermally stratified shear layer. Effects of buoyancy on the mean flow and turbulence were studied. Both stable and unstable stratified layers were realized. In the stable stratified flow the highest Richardson number is around unity.
The velocity gradient either increases or decreases depending on whether the flow is unstable or stable. Correspondingly, the turbulence intensity is reduced with increasing stability, whereas under unstable conditions it is enhanced. The measured thermal flux shows a remarkable difference in stable and unstable layer.
With an appropriate normalization the spectra and cospectra changes according to the Richardson number at low frequencies, however they collapse into a single universal curve at high frequencies. This agrees very well with results of field observations.

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Unsteady problem of a viscous incompressible flow in free space is investigated, and a class of exact solutions of the Navier-Stokes equation is given for a general initial condition. This flow field represents several shear layers superimposed on an irrotational, three-dimensional straining flow. This solution incorporates the three representative aspects of vortex motion : stretching, convection and viscous diffusion of vorticity. The solution is exemplified for several kinds of initial condition. One of them represents a flow approaching a steady state in which the above three effects are brought to an equilbrium. Another solutions show collision of two shear layers in various arrangments : e. g. two parallel layers merge into a single layer, two antiparallel layers (in which the vortices in the two layers are in the opposite directions), disappear as pair annihilation and two layers merge like vectors by oblique collision. It is also shown that N shear layers, in general, merge like vectors.

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