Development of measurement system for micro-scale impact load in cavitation bubble collapse

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When the cavitation occurs in turbo machinery and cavitation bubbles collapses inside the machinery, impact loading causes cavitation erosions. This study aims at developing the measurement system of the micro-scale impact load remotely by inverse analysis. Impact experiments due to bubble collapses initiated by electrical sparks under water were conducted at the bottom of the thick polycarbonate rod. The AE signals were measured at the top of the rod, 100 mm from the bottom. The bubble generation and collapsing were recorded by high-speed video camera. The impact forces are estimated by inverse analyses and the transfer function for estimating the impact forces was determined by the mechanical pencil lead press-breaking method. The impact forces estimated by the analyses revealed that the first loading was caused by the arrival of the shock wave due to the electric spark and the maxim loading was observed when the water jet in the bubble collapse reached at the bottom surface.