It is important to explain a high-speed liquid flow phenomenon because of the developments of various fluid machines. Cavitation is one of the most important phenomena in high-speed liquid flow. When cavitation appears in a liquid flow, it causes some problems such as performance deterioration, vibrations, noise, and cavitation damage. So, it is important to observe the cavity behavior to solve such problems. Especially, it is well known that a cloud cavitation has heavy unsteadiness and high impulse. In this study, a fundamental experimental research on the process of growing to the cloud-like cavitation was performed. The aspect of the cavitation in a circular cylindrical orifice and in a convergent-divergent channel was observed by the high-speed video camera. As a result, the unsteady shedding behavior of the vortex cavity was characteristically observed in a region of the separation bubble at an inlet of a circular cylindrical orifice. There are several vortex cavities on the separated shear layer. These cavities behave pairing and coalescence with each other repeatedly and grow up into a cloud-like cavity. The cloud-like cavity is shed downstream and then generates high impulses at the collapse. In the case of a circular cylindrical orifice, the cavities can be observed clearly by using a laser sheet method. Similar behaviors of the cavity are observed on the separated shear layer in a two dimensional convergent-divergent channel. This paper discusses how the behaviors of vortex cavity relate closely to the flow pattern at non-cavitating condition on the separated shear layer and that the process of the vortex cavities develop to the cloud-like cavity.

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