A Study on Improvement of Performance of Ship Propulsion Device Directly Driven by Steam

通过高速摄像机对喷嘴内部流动进行可视化，可以看出喷嘴内部的流动不是空气和水的混合流，而是空气和水分离的流动，并且在界面上出现大幅值的波动。这些波关闭了空气流，压力上升，压力使水加速流向下游。研究还表明，加速水的机制不是混合，而是空气压力加速水的体积而不混合。因此，损失小于混合机制。在间歇发射的情况下，推力本身并没有增加，但考虑到发射持续时间，间歇发射的推进效率更好。采用有限差分格子Boltzmann模型对两种流体进行数值模拟，得到了较好的结果。在两种流体之间的界面上，出现大振幅波。但是在这个模型中，两种流体的密度是相同的，于是我们尝试对双流体模型进行改进。密度差对应于加速度差，因此通过修改加速度可以模拟密度差。对于单相流，这种技术被证明是成功的。本文还介绍了一种新的多原子气体比热选择模型。

By visualizing the flow inside the nozzle by high-speed video camera, it is shown that the flow is not a mixed flow of air and water but a flow in which the air and the water are separated and waves with large amplitude appear on the interface. These waves close the air flow and the pressure rises and the pressure accelerate the water, towards downstream. It is also shown that the mechanism in accelerating the water is not mixing but the volume of water accelerated by air pressure without mixing. So the loss is smaller than the mixing mechanism. The case of intermittent emission, the thrust itself does not increase, but the propulsive efficiency considering the emission duration, the operation of intermittent emission is better.The numerical simulation by the finite difference lattice Boltzmann model for two fluids gives good results. On the interface between the two fluids, large-amplitude waves appear. But in this model the densities of the two fluids are the same, then we tried to improved the two-fluid model. The density difference corresponds to the acceleration difference, so by modifying the acceleration the density difference can be simulated. For single-phase flows, this technique is shown to be successful. A new model with choosing specific heats for multi-atomic gas is also introduced.