The characteristics of thrust for ship propulsion equipment directly driven by air compressed by pressure fluctuation in a blower piping system are investigated. The pressure in the piping system with a discharge opening under the surface of water is measured for the depth and the cross-sectional area of the discharge opening. An exhaust valve is positioned upon the air ejection hole, and the effects of the valve on the pressure in the pipes and the thrust for the propulsive nozzle were examined. The following results were obtained. The pressure fluctuation owing to the columnar resonance or Helmholtz resonance occurs at the certain specific depth or cross sectional area of the discharge opening. The pressure in the pipes decreases immediately after the exhaust valve was opened, and it increases just before the valve is closed. The dominant frequency of the pressure fluctuation in the pipes agrees with that of the opening-closing cycle for the exhaust valve. The thrust for the propulsive nozzle monotonically increases with increasing number of revolutions and depth. The interfacial wave in the nozzle appears in the frequency of approximately 4Hz, and it is important for the increase of the thrust to synchronize the opening-closing cycle for the exhaust valve with the generation frequency of the interfacial wave. The finite difference lattice Boltzmann method is helpful to investigate the characteristics of the flow in the nozzle.

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