水下脉动气泡能量耗散特性研究

Underwater bubble dynamics is a fundamental issue concerned in fields including oil petroleum extraction, chemical industry, ocean environment, medical science, et al. Dispite the numerous researches done previously, the effort is still not sufficient due to the complexity of bubble motion charactristics, and the mechenisms of many phenomenon remain to be discovered. When the underwater explosion bubble is formed, the velocity of bubble surface is rapid and its inner temperature can reach 5000K. Energy transfer phenomenon between the inner bubble and the surrounding fluid field exists during bubble impulsation which results in the decrease of its maximum radius. Starting with the basics of bubble motion, improvements are made to the traditional incompressible potential-flow theory based on constant entropy process which fails to represent energy loss in bubble pulsation. The features of bubble energy dissipation are explored during bubble pulsation process. Three methods are applied to study the energy dissipation of bubble impulse. 1). Based on wave equation, heat conduction equation and phase transition equation, three dimensional numerical model is built with the consideration of different energy dissipation process. 2). The affectness of different energy dissipation features to bubble collapse and jet features are studied. 3). High voltage spark generator is to be designed to study bubble motion and jet features near different boundaries and to verify the effectness of the numerical model, which aims to provide references to bubble dynamic field.

水中气泡的动态特性一直是很多领域关心的重要基础性问题，气泡应用十分广泛，包括石油开采、化学工业、海洋环境、医疗等领域。由于气泡运动的复杂性，人们对气泡种种特性的研究仍不够充分，很多未知的机理有待探索。例如水下爆炸气泡形成初期，气泡运动速度很快，内部温度高达5000K，其脉动过程中与周围流场存在着能量交换，导致其最大半径逐渐减小。本研究拟从气泡运动的基本现象入手，针对以往采用基于等熵过程的不可压缩势流理论求解气泡脉动导致其能量不损失的缺陷，探索气泡脉动中能量耗散的机理，主要研究内容包括：1）、分别基于波动方程、热传导方程和相变平衡方程，建立计及不同能量损失过程的气泡动力学三维数值模型；2）、研究不同能量耗散特性对气泡坍塌、射流等重要动力学行为的影响；3）、设计水中高电压电火花气泡生成器，研究不同边界条件下气泡运动及射流特性，验证本研究建立数值模型有效性，旨在为气泡领域相关研究提供参考。

水中气泡在各个领域广泛存在，充满了神秘。气泡不同领域，如船舶、海洋、医疗等领域的应用也十分广泛。长期以来，人们对水中气泡的运动特性做了大量的研究工作，但由于气泡运动的复杂性，气泡的种种特性研究仍不够充分，有很多未知的机理有待研究人员探索。水下爆炸气泡载荷会对水中结构物造成严重毁伤，严重时会导致其丧失生命力，因此精确的水下爆炸气泡脉动数值模型是首先要解决的问题。本项目从气泡运动的基本现象入手，针对以往不可压缩势流理论中气泡脉动能量不损失的理论缺陷，基于波动方程，提出了考虑流场中可压缩性的边界积分方程；其次基于热传导方程，建立气泡内部与周围流场间的热交换的数值模型，模拟气泡脉动过程中内部热量的分布规律；再次，基于能量法，建立了可以同时考虑流场可压缩性、热传导特性及物质传递特性等能量耗散过程的数值模型，模型简单，容易计算；最后设计并研制了水下高电压气泡生成装置的样机，自由场中生成气泡半径约为36mm，且有明显的浮力效果，为真实水下爆炸气泡脉动特性的研究提供了较为真实的爆炸源，在此基础上研究不同边界条件下气泡的运动特性。