A theoretical study is made on the viscous flow past a cylindrical hole (radius R₀) bored inside an otherwise unbounded homogeneous porous media (permeability K). This situation occurs, for example, in measurement of the subterranean water flow by means of the single boring method. The fluid far from the hole is assumed to be a uniform constant velocity U_∞, and the entire flow field is obtained by matching a solution of the Stokes equation inside the hole with that of the generalized Darcy's equation in the porous region. In general, the effect of the hole increases with the value of ζ₀ (=R₀/√k).When ζ₀ is much greater than unity, which corresponds to the case for underground water flow, the velocity at the center of the hole becomes 3U_∞, while the volume flux fiowing into the hole from upstream-side becomes twice, in comparison with that flowing into the same region in the absence of the hole. The present results show many differences from those obtained on the assumption that the hole region is a porous media of infinitely high permeability.

View full abstract

The flowfield produced by a vortex ring approaching a sphere was investigated mainly by means of smoke visualization technique. The main result obtained was that a vortex ring could pass over a sphere, although a vortex pair, i. e. the two-dimensional case corresponding to a vortex ring, could not pass over a cylinder, and the generation of the secondary vortex ring due to separation and the subsequent interaction with the main ring could be observed. Some characteristics of the ring before and after the pass-over were measured and the decays of circulation and kinetic energy were estimated by using the results.
Some numerical calculations based on both Lewis' solution and Wang's solution were carried out in order to obtain some information about the viscous effects in the actual flowfield. The difference between calculated and measured results was remarkable after the pass-over, because the separation was not taken into account in both theories.

View full abstract

A wind tunnel experiment was made on the intermittent region of the turbulent boundary layer. The conditional sampling and average measurement in the turbulent bulges revealed a pair of rotating flow. The structure of the turbulent bulges can be explained by the model of a pair of banana-vortices.

View full abstract

In LIB ICF (inertial confinement fusion driven by a light ion beam), a cryogenetic hollow shell target (consisting of three layers) irradieted by LIB implodes in the way of a cannon ball type. The implosion velocity is derived by using a hydrodynamic model under the following assumptions; (1) adiabatic and spherically symmetric compression, (2) neglect of instabilities and nonuniformity caused by an implosion motion.
The output energy of LIB ICF depends greatly on the implosion velocity depends on some parameters of the target. The optimal values of the target parameters are calculated in order to obtain the maximum output energy.

View full abstract

A row of longitudinal vortices is produced at edges of several thin plates placed just outside a turbulent boundary layer on a flat plate. The vortices result in the strong spanwise variation of the boundary layer thickness. Measurments indicate that distributions of mean-and fluctuating-velocity are similar at various spanwise positions. A spot with negative production of fluctuation energy is found in the region of upward velocity.

View full abstract