不同环境下气泡脉动特性实验研究

水下爆炸气泡对舰船结构造成严重的毁伤, 海上实船爆炸实验是考核水下爆 炸气泡对舰船毁伤威力最直接、最有效的方法, 然而真实情况的舰船水下爆炸实验难以进行. 为此, 在已有研究成果的基础上, 设计实验电路, 利用电容在相对较低的电压下放电打 火产生的电火花气泡来模拟水下爆炸气泡, 设计多组实验工况来模拟气泡在不同环境下的运 动特性. 研究气泡在不同环境下的脉动特性、射流特征, 揭示一些特殊的实验现象, 总结环 境对气泡运动的影响规律.

EXPERIMENTAL STUDY ON BUBBLE PULSE FEATURES UNDER DIFFERENT CIRCUMSTANCES

Underwater explosion bubbles do severe damage to warship structures, and the particularity of underwater explosion and the quality of water bring great difficulties to get a clear picture. So lots of laboratories all around the world make use of discharge or laser to generate bubbles to replace real underwater explosion experiments. Based on the designation from Turangan et al and Abdolranman Dadvand, an electric circuit with a relatively low voltage 200V and three shunt-wound 2200\muF capacitances is used to generate bubbles by discharge in a 500mm\times500mm\times500mm water tank to study underwater bubble dynamics. The experiment setup is safe, stable, low in costs and simple to fix. It can generate bubbles with radius up to 12~15mm. A device generating bubble by a relatively low voltage is designed to study bubble dynamics in detail under various boundary conditions in this paper. Main conclusions are obtained below by comparison and analysis: (1) A voltage of 200 V is adopted to generate bubble by discharge in water in this paper. The voltage is fairly low yet the bubble generated is relatively large in size. The pictures shot are pretty clear as well. (2) There are copper wires burning inside the bubble throughout the expansion process, causing the temperature inside bubble to rise apparently higher and result in the small calculated value of bubble pulsing period. So p_v within the bubble is actually very large and the calculated p_v of a single bubble pulsing in free field is 5.8\times 10^4 Pa. (3) Bubble's second pulsing energy is merely 5{\%}\sim 15{\%} of the first pulsing energy and the pulsing energy after the second pulse can be ignored. (4) \gamma , the dimensionless standoff is defined between bubble and boundary. When \gamma \ge 2.8, the influence of the wall to bubble can be neglected. When 1.95 \le \gamma \le 2.8, no jet is formed during the first cycle of bubble pulse. When \gamma \le 1.53, jet is formed during the first cycle of bubble pulse, and the smaller \gamma is, the larger bubble migration distance and the more fiercely the jet would be. (5) The bubble jetting velocity is minimum when the dimensionless standoff \gamma is around 0.8. (6) Bubble will interact strongly with boundaries when it moves near the shipboard and the free surface. It can be seen from the experiments that the bubble may produce jets that are towards two different directions when collapsing near the free surface and the shipboard, and this will certainly lead to the weakening effect of bubble attack to the shipboard.