Numerical study on the flow field and load characteristics of a head-ventilated revolving body during water entry
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摘要: 为探究周向通气对回转体入水表面载荷的影响，基于VOF(volume of fluid)模型和Realizable k-ε两层湍流模型，开展了周向通气回转体低速入水流场演化数值预报和表面载荷特性分析。通过将数值预报的空泡形态与试验结果相对比，验证了所采用的数值方法的有效性，并分析了不同通气率对空泡形态、流场特性和表面载荷特性的影响。结果表明，通气会改变回转体入水空泡演化过程以及侧壁表面压力，在通气作用下空泡第一次脱落时间延缓，并且通气气体流向空化器后方负压区，改善了空化器后方的负压情况；其次，通气气体在通气口附近形成了明显的涡结构，之后与壁面处由空化器形成的涡融合，增强了空泡中部的涡流强度；最后，通气率越大，空泡闭合时间越晚，空泡体积越大，尾部空泡越不容易发生脱落，同时通气会减缓回转体表面的压力波动，通气率越大压力波动越小。综合分析可以认为，侧向通气对于回转体低速入水流场及表面载荷特性有一定的改善作用。Abstract: To study the influence of side-direction ventilation on the surface loads of a revolving body during water entry, based on the VOF (volume of fluid) model and the Realizable k-ε two-layer turbulence model, the numerical prediction of the flow field evolution and analysis of the surface load characteristics when a side-direction ventilated revolving body into the water at a low-speed are carried out. By comparing the cavity shape between the numerical predictions and the experimental results, the validity of the numerical method is verified. The effects of different ventilation rates on the cavity shape, the flow field evolution, and the surface load characteristics are then analyzed. The results show that ventilation changes the process of the cavity evolution and the pressure on the sidewall surface of the revolving body. With the effect of ventilation, the time when the first cavity falls off is delayed, and the ventilation gas flows to the area behind the cavitator, which improves the negative pressure situation behind the cavitator. The ventilation gas forms an obvious vortex structure near the spout, which then merges with another vortex formed by the cavitator at the cavity wall, leading to an increase in the vortex intensity in the middle of the cavity. With the increase of the ventilation rate, the closure time of the cavity becomes later, the volume of the cavity gets bigger, and the cavity near the tail of the revolving body is less likely to fall off. Compared to the non-ventilation situation, the ventilation will reduce the fluctuations of the surface loads. The greater the ventilation rate, the less the surface load fluctuations are. In general, the side-direction ventilation improves the flow field and the surface load characteristics of the revolving body during low-speed water entry.
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Key words:
- revolving body /
- head-ventilation /
- water entry /
- flow field evolution /
- surface load
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图 3 数值模拟得到的空泡形态与试验结果的对比
Figure 3. Comparison of cavity shape between numerical simulation and experiment
图 5 t=10～40 ms时回转体侧壁表面相对压力
Figure 5. Relative pressure of revolving body at t=10～40 ms
图 9 监测点P1、P2在不同通气率条件下的压力时间曲线
Figure 9. Pressure-time curves at point P1 and P2 at different ventilation rates
表 1 空泡最大直径及长度
Table 1. Maximum diameter and length of cavity
时间/ms 空泡最大直径/mm 空泡长度/mm CQS=0 CQS=0.5 CQS=0 CQS=0.5 10 51.2 52.0 78.5 79.0 20 46.8 56.8 102.3 115.8 30 44.7 49.6 129.0 147.7 40 43.0 48.0 130.0 176.9 50 43.1 48.0 118.3 177.1 60 43.0 48.0 121.3 184.2 
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