The drag reduction is needed for the economical ship operations and the suppression of CO2 emission. Microbubble injection is one of the promising techniques for the purpose. It was experimentally confirmed that the skin friction could be reduced remarkably, by injecting the microbubbles with the diameter of 0.5 to 1.0mm from the bottom of a ship hull. Although a great number of papers can be seen in the literatures, unfortunately, the efficient and accurate computer code, which can calculate the global flow phenomenon around a ship hull and can be used in the ship design, has never been developed. In the present study, the correlations between liquid and microbubbles are modeled and computed, by using the two-fluid model. The Reynolds stress transport model is employed for the accurate prediction of the bubble behavior around a ship. The present model is tuned and verified, based on the fundamental experiment conducted by Kodama et al. in 2000. Furthermore, using the present model, the drag reduction mechanism by microbubbles is numerically investigated for a wide variety of void fraction and flow conditions. It is confirmed that the present Reynolds stress model can capture the characteristic of drag reduction by the microbubbles.

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