A two-dimensional open type nozzle has been investigated for ship propulsion equipment. In this nozzle, a high-pressure gas (air) is ejected from below into water flow and accelerates the water towards downstream. Two cases, continuously and intermittently ejection of gas, are studied. In the latter case, the thrust itself is smaller than that in the former case, but thrust based on the ejection duration is larger. Even in the continuously ejected case, it was found that the gas phase and the water phase are separated. The water waves of large amplitude appear on the interface inside the nozzle and these waves propagate towards downstream. A numerical study by the lattice Boltzmann method was also performed to clarify the flow inside the nozzle.

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