| Research Abstract |
An experimental study was made of the problem concerned with the ultra-high speed liquid flow phenomena by means of a vertical from of light gas gun. First we conducted a preliminary experiment to obtain the relationship between powder mass and sabot flyer velocity. Using a 2g plastic sabot flyer, we obtained the flyer velocity ranging from several hundreds meters per second up to 2km/s. Based on the data obtained, we rushed a flyer from the above into water and observed the sequential surface phenomena such as the deformation of a free surface, the surface closure and the splash. We also observed the behavior of a cavity formed behind the substance moving into water. In the later stage of the substance movement, a cavity was fully developed and finally separated from the surface. Aftre the separation, an interesting phenomenon, a reentrant jet, occurred at the rear side of the closed cavity. It was flowing toward the substance. This kind of experiment was carried out for two test liqu
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ids, water and glycerin, in order to evaluate the liquid viscosity. Furthermore we found that cavitation bubbles generated during this process were strongly influenced by the adjacent cavity surface. In relation to this problem, an experimental study was made of a laser-produced bubble near a free surface. Consequently, we had some information about the bubble migration such that a free surface repels a bubble collapsing from the boundary. The behavior of two bubbles not only in phase but ou t of phase was also experimentally examined in detail.
On the other hand, we investigated the problem of a pulsed water jet which belongs to be one of the typical examples of ultra-high speed liquid flow phenomena. A 1.15g plastic sabot, which has a ditch at its front side for carrying a little amount of water, impacts on a sabot stopper, thereafter theparated water goes ahead through a small hole inside the sabot stopper, like a nozzle, due to the inertia and finally impacts with the maximum velocity of 1.5km/s against a target which was set in the vacuum state. A pulsed jet emerging from the nozzle exit becomes unstable at the mixing layer, producing a large number of minute droplets. We observed a lot of microscpic erosion, so-called damage pit, on the surface of the target. They must be formed due to the high speed impacts of individual droplets. Less
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