Bubbly structures in a cavitating slot orifice

• Cavitation of bubbly structures in a confined geometry were studied experimentally.
• Technique: high speed video, micro resistivity probes, micro optical pressure probe.
• Flow regimes identified: limiting regime versus developed cavitation.
• Threshold of cavitation inception or cavitation disappearance.
• Bubble cloud was formed by clustering of growing bubble nuclei after the breakup.

The research refers to the experimental study of cavitation phenomena when water was passing through the slot orifice. The contribution brought up by this article is the detailed time and space dependent analysis of bubbly structures identified using high speed video, microresistivity probes, optical fibre pressure probe, and hot film probe. Two principle experiments were carried out to study cavitation in a confined geometry. The first one was designed to study an induced single bubble cavitation when the water pressure was reduced below the atmospheric pressure, but was still high enough so that there was not any saturated pressure in the slot region. The second experiment was undertaken at a reference pressure which was sufficient to produce a massive cavitation in the slot region. The following flow regimes were identified and analyzed in detail: the so-called detachment regime where bubble breakup was observed in the case of the individual bubble cavitation; and in the case of the large scale cavitation, the regime of macroscopic bubbles clustering into bubble cloud and the regime of collapsing bubbles.