A study on jet flow induced by underwater explosion at a pit-interface
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摘要: 利用液滴坠落冲击直管中水平液面产生半球形凹陷，并以此凹陷液面作为初始界面进行水下爆炸冲击诱导射流的实验研究。以高速摄影为主要手段，结合Fluent数值模拟，揭示了凹陷液面在水下爆炸冲击作用下的变形过程和机理。实验结果表明，随着爆炸的发生，液面凹陷中心会汇聚形成纤细光滑的射流，同时在管壁附近会产生附加环状射流，这明显区别于冲击直管中水平液面诱导射流的现象。进一步研究发现，中心射流的产生主要源于液面凹陷对爆炸能量的汇聚作用，而附加射流的产生受到液面初始形状和管壁剪切阻力的共同影响，二者经历短暂的加速过程之后均以一个近似恒定的速度向上抬升。通过考察能量对射流的影响发现，中心射流与附加射流的速度均与充电电压(爆炸能量的1/2次方)呈线性正相关；中心射流形态特征基本不变，附加射流则随能量的变化呈现不同的形态。Abstract: In this study we conducted an experiment on the jetting flow induced by underwater wire explosion at an interface with a quasi-static hemispherical pit, in which the interfacial pit was created by the dripping of a liquid drop. Further, using high-speed video photography and Fluent numerical simulation, we revealed the development and features of the jetting flow, tested and verified the applicability of the pit creation method. The experimental results show that the explosion induces a slim and smooth central jet that arises from the bottom of a pit, and a circular side jet arises from the boundary region of the tube, which differs from the known jetting phenomenon without a pit at the surface. Further study reveals the central jet is a result of the energy concentration effect of the pit under impact and the circular side jet is caused by a combined effect of the disturbed initial interface and the friction of the tube wall. Both jets rise with an early constant velocity after a short acceleration process. Examination of the explosion energy indicates that the velocities of the two jets increase linearly with the charging voltage (or equivalently the square root of the explosion energy).The explosion energy barely affects the general feature of the central jet but has a significant influence on the appearance of the side jet.
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Key words:
- jet /
- underwater explosion /
- straight tube /
- falling droplet /
- pit
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图 1 实验装置示意图以及液面凹陷随时间的变化过程
Figure 1. Schematic of experimental setup and the evolution of a pit varying with time
图 2 数值模拟中初始界面的简化设置方法和初始压力为2.84 MPa时的数值模拟结果
Figure 2. Simplified setup of the initial interface in the numerical simulation and numerical simulation results at 2.84 MPa
图 3 不同冲击能量下气柱上沿(金属罩)位置随时间变化
Figure 3. Air length varying with time under different impact energy
图 4 冲击直管中凹陷液面诱导射流发展的高速摄影图像
Figure 4. Sequential images of the jetting flow in a straight tube with a pit on initial liquid surface
图 5 不同时刻压力及射流顶点位置模拟结果(p0=2.84 MPa)
Figure 5. Pressure and location of jet tip at different times (p0=2.84 MPa)
图 6 倾斜拍摄的射流发展过程图像(Uc=200 V)
Figure 6. Experimental result of upper oblique view of the jetting flow (Uc=200 V)
图 7 滑移边界模拟结果(p0=2.84 MPa)
Figure 7. Numerical simulation results with slip wall (p0=2.84 MPa)
图 10 气柱最大速度与中心射流速度和附加射流速度对比
Figure 10. Maximum bubble velocity versus central jet velocity and additional jet velocity
表 1 各个工况的模拟压力和对应的实验充电电压
Table 1. Initial pressure of simulation corresponding to charging voltage of experiments
工况 p0/MPa Uc/V 1 1.60 150 2 2.84 200 3 4.44 250 4 6.40 300 5 8.70 350 
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