The reduction of propeller efficiency in a bubbly flow is numerically studied in this study. The model used is a two-fluid multiphase flow model of which the governing equations are the mass and momentum conservation of the mixture and the bubble phases. The validation of model was carried out using experimental data for a 2D hydrofoil. The results of the simulation were investigated in detail in order to explain the decrease of the propeller efficiency in bubbly flows. It was shown that bubbles are relatively accelerated around the leading edge of a hydrofoil or a propeller blade, and that the acceleration of liquid is reduced due to the bubble acceleration. This effect lowers the peak of the negative pressure at the leading edge resulting in the decrease in the lift and the increase in the drag coefficients. Finally the model was applied to the prediction of the propeller efficiency in bubbly flow, and the results agreed with the experimental results.

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