MECHANISM CREATING IMPULSIVE-FORCE DUE TO VORTEX CAVITATION BUBBLE WTTH HIGH EROSIVE POWER

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In the present research, a circular and a triangular cylinder were used as a cavitating body. Two kinds of circular cylinders were chosen to investigate the three-dimensional characteristics of bubble behaviors toward the freestream direction as well as the wall-direction. A triangular cylinder was used for high-speed flow experiments and cavitation erosion-impulsive pressure tests.A simultaneous measurement system for instantaneous appearance at bubble collapse and impulsive pressure, as well as instantaneous appearance at bubble collapse and an erosion pit, was made up, especially for the purpose of an anlysis of a cavitation bubble pattern with high impulsive force and was used for the above-mentioned test bodies. As the result, the process of bubble collapse is approximately divided into three patterns, A) three-dimensional radial collapsing motion at a slight distance from the solid wall boundary, B) axial collapsing motion toward the solid wall boundary with an impinging rapid movement.C) two-dimensional radial collapsing motion keeping the orginal slender shape.The collapsing patterns like this was also examined from the relation with the erosion effects. For the type-B pattern, especially, the vortex cavitation bubble shows a typical singular behavior near the solid wall compared with the inside of flow and the vortex cavitation bubble pattern with an axis perpendicular to the solid wall has a special strong impulsive force. The measurement method using an impulsive pressure sensor for cavitation attack is proposed together with a simultaneous measurement method of the erosion pits and the bubble collapsing behaviors.In order to solve the mechanism of impulsive force generation from a vortex cavitation bubble, the simultaneous measurement method of high-speed-video observation with the impulsive force and/or the erosion pits are developed so that the results are experimentally discussed. As a result, the valuable data are shown quantitatively.