The simultaneous measurements of the bubble collapsing behaviors and the impulsive force were taken for vortex cavitation bubbles in the vicinity of the flow path wall under a real flowing condition behind a circular cylinder. Especially, the bubble collapsing motion toward the solid wall, namely a spanwise-view of a circular cylinder, was examined near the final collapse stage. It is experimentally found that the bubble collapsing behavior in the proximity of the wall is generally classified into three patterns. They are type-A; a quasi-spherical collapse at a distance from solid wall, type-B; a collapse with an impinging motion toward solid wall and type-C; a collapse keeping a long slender shape of bubble. Many simultaneous measurements were taken about the bubble collapsing behavior and the impulsive force. As a result, it is confirmed that the collapse pattern of type-B causes a relatively large force. For the collapsing behavior of type-B, a rapid deformation and motion toward the wall is observed. This suggests the existence of high speed flow to the wall. The deformation velocity is estimated to reach the order of at least 20-30 m/s. This experimental evidence for type-B should be noted from a standpoint of cavitation impulsive pressure as well as a quasi-spherical collapsing pattern of type-A.
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