﻿ 波浪中KCS船气泡减阻效能计算分析
 舰船科学技术  2024, Vol. 46 Issue (12): 53-59    DOI: 10.3404/j.issn.1672-7649.2024.12.009 PDF

The drag reduction effectiveness of KCS ship bubbles in waves was calculated and analyzed
WU Bin, WANG Zhibo
Ocean Engineering College, Jiangsu Ocean University, Lianyungang 222006, China
Abstract: With the increasing emphasis on energy conservation and emission reduction worldwide, how to efficiently reduce ship resistance has become one of the key concerns of China's shipping industry. To solve the problem of high energy consumption and friction resistance when ships navigate in waves, the drag reduction efficiency of ship bubbles in waves is analyzed. The KCS container ship model developed by the Korea Institute of Ship and Ocean Engineering is taken as the research object. Based on Euler multiphase flow, micro bubbles are introduced into the bottom of the ship, the interaction between gas and liquid is considered, and the ship speed and the diameter of the vent hole are kept constant. The effects of wave height and wave length changes on the gas volume fraction and the total resistance of the ship under different ventilation volumes are studied. The results show that the higher the wave height, the more intense the ship's motion and the greater the resistance; The change in wavelength to length ratio under a certain ventilation capacity can also have an impact on ship resistance. Based on the experimental results, the mechanism of the coupling effect between wave drag enhancement and bubble lubrication drag reduction was discussed in the form of curves and cloud charts, and the impact of changes in ventilation on the drag reduction effect was analyzed from the perspective of energy conservation.
Key words: bubble drag reduction     wave action     coupling effect     energy conservation
0 引　言

1 数学模型 1.1 KCS船型的阻力成分

 ${R}_{T}={R}_{f}+{R}_{w}+{R}_{pv} 。$ (1)

 ${R}_{f}={R}_{f1}+{R}_{f2}+\Delta {R}_{f}。$ (2)

 ${R}_{T}={R}_{f1}+{R}_{f2}+{R}_{w1}+{R}_{w2}+\Delta {R}_{f}。$ (3)

 ${R}_{f1}=\frac{{R}_{t2}}{{R}_{t1}} ，$ (4)
 ${R}_{f2}=\left(1-\frac{{R}_{t2}}{{R}_{t1}}\right){R}_{f}。$

1957年国际船模试验池实船-船模换算公式，简称1957ITTC公式：

 ${C}_{f}=\frac{0.075}{{(lgRe-2)}^{2}} 。$ (5)

1.2 气液两相流数学模型

1）气液两相流连续方程：

 $\frac{{\partial \rho }_{m}}{\partial t}+{\mathrm{div}}\left(\rho {V}_{m}\right)=0。$ (6)

2）气液两相流运动方程：

 $\frac{\partial \left({\beta }_{\rho }{V}_{i}\right)}{\partial t}+{\mathrm{div}}\left(\rho {v}_{i}{V}_{m}\right)={\mathrm{div}}\left({\mu }_{m}grad{V}_{i}\right)-\frac{\partial p}{\partial i}。$ (7)

3）气液两相流体积含气率方程

 $\frac{\partial \left({\beta }_{\rho }G\right)}{\partial t}+{\mathrm{div}}\left(\beta {\rho }_{G}{V}_{m}\right)={\mathrm{div}}\left({D}_{s}grad\left({\beta }_{\rho G}\right)\right)。$ (8)

2 数值计算模型 2.1 模型构建与网格划分

 图 1 KCS船三维视图 Fig. 1 Three-dimensional view of KCS ship

 图 2 KCS船底部视图 Fig. 2 Bottom view of KCS vessel

 图 3 KCS船底打孔视图 Fig. 3 View of KCS bilge perforation

 图 4 KCS船体网格分布 Fig. 4 KCS hull grid distribution

 图 5 试验池网格分布 Fig. 5 Grid distribution of the test cell
2.2 边界条件设置

1）给定计算域水流进口（船首方向）为速度进口，计算域的顶部与底部均为速度进口

2）水流出口（船尾方向）为压力出口

3）船体对应试验池的两侧均为对称平面。

4）船体表面均设置为无滑移壁面边界，这样设置使气液两相流无法穿透船体表面。

5）气泡入口即孔的位置设为质量流量进口，且速度进入时垂直于船体表面。

 图 6 边界层划分 Fig. 6 Boundary layer division
3 船舶在波浪中的运动计算工况 3.1 波高变化对KCS船模微气泡减阻影响

KCS船在波浪中运动时，会发生纵摇与垂荡变化，故船舶总阻力也会随之发生一些变化，故船舶总阻力最终结果以平均值的形式展现。本实验及考虑船舶横摇和深沉2个自由度时的运动，表3所示为不同波高下KCS船不通气与通气量为0.00088 kg/s时的阻力值。

 $\gamma =\frac{{R}_{t0}-{R}_{t}}{{R}_{t0}}\times 100{\text{%}}。$ (9)

 图 7 KCS船模减阻率随着波高变化情况 Fig. 7 Variation of KCS ship model drag reduction rate with wave height

 图 8 不同波高下KCS船模减阻率 Fig. 8 KCS ship model drag reduction rate for different wave heights
3.2 波长船长比变化对KCS船模微气泡减阻的影响

 图 9 hB=0.05 m，λ/l=0.5，不同通气量下总阻力减阻率变化 Fig. 9 Variation of total resistance reduction rate under different ventilation with hB=0.05 m and λ/l=0.5

 图 10 hB=0.05 m，λ/l=0.75，不同通气量下总阻力减阻率变化 Fig. 10 Variation of total resistance reduction rate under different ventilation with hB=0.05 m and λ/l=0.75

 图 11 hB=0.05 m，λ/l=1，不同通气量下总阻力减阻率变化 Fig. 11 Variation of total resistance reduction rate under different ventilation with hB=0.05 m, λ/l=1
4 波浪对气泡边界层的运动诱导规律分析

KCS船舶在设计时充分利用了光平面原理，这种原理提出，通过锥体来缩小船舶和水的接触面积，减少摩擦阻力和湍流。KCS船舶尾部采用斜线型的造型，减小了与水的接触面积，节省了能源。此外，为了降低摩擦阻力和波浪阻力，KCS船体曲线高度优化。采用了一系列的复合曲线曲率变化的设计，并且底部有前至后的S形曲线，减小了阻力，提高了速度。

KCS船舶的边界层和释放气泡减阻机制之间存在一定关系。在KCS船舶表面，有一定微观粗糙度，而通过释放气泡，可在表面形成一个带有微小气泡的气动边界层，这个气动边界层可改善船体表面的流场结构，从而使边界层流动发生变化，降低摩擦阻力，实现减阻。具体来说，KCS船身在航行过程中，会引入适量的空气或水，产生气泡或汇聚成“壁垒”，形成一种特殊的减阻模式，这些气泡阻碍了流体与壁面直接接触，减少了壁面上垂向运动的强度，并通过扰动流、延缓已形成龙骨线区域强流进行作用，在被扰动较为严重的流动区域路程上，实现摩擦阻力的显著降低。因此，释放气泡是实现KCS船舶边界层减阻的一种有效机制。漩涡是由流体运动引起的旋转流，在船旁边形成会对船的表面产生扰动并使边界层分离。边界层分离会导致阻力增加，从而减缓船速。

 图 12 通入气泡后边界层画面 Fig. 12 Boundary layer after bubble introduction

 图 13 KCS船不同边界层内空气体积分数分布 Fig. 13 Air volume fraction distribution within different boundary layers of KCS ship

 图 14 KCS船气泡逃逸通路 Fig. 14 KCS ship bubble escape pathway
5 气泡减阻效能评估

 $\Delta p1=\Delta {R}_{t}\times v 。$ (10)

 ${p}_{2}=0.5\times A\times \rho \times v 。$ (11)

 图 15 单位时间内通出气体的动能 Fig. 15 Kinetic energy per unit time of the fluxed gas
6 结　语

1）舶波浪阻力增值随着波高的增加而增加，遭遇的波浪越大，船体运动越剧烈，阻力越大。

2）船速和气泡直径不变的前提下，通气量在一定范围内变化时，船舶减阻率随着通气量的增加而增加。

3）船长比值为一定值时，船舶减阻率先是随着通气量的增加而增加，通气量增加到一定值时，船舶减阻率随着通气量的增加而减少。

4）间内通出气体的动能在一定范围内先是随着波长的增加而减少，而后又随着波长的增加而增加

5）仿真结果表明$\lambda /l$=0.75单位时间内通出气体动能达到最高，气泡最大程度吸收了部分能量，缓解了波浪对船体的冲击，降低了燃油消耗，提高了船舶速度。

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