掺气泡对近壁区空泡演化和壁面压力的影响机理研究

Aeration has become the most economical and effective measure to prevent cavitation for high-speed flow. However, the mechanism of reducing cavitation using aeration still is not clear. In order to solve this problem, basing on the vacuum tunnel, a testing system is established to measure simultaneously evolution of cavitation bubble shape, wall pressure and cavitation noise. Meanwhile, based on the advantage of microscopic characteristics and mesoscopic background, lattice Boltzmann method’s algorithm is simple and suitable to parallel computing; also, its boundary condition can be implemented easily. Furthermore, it can track automatically the phase interface. So, a lattice Boltzmann model for two-phase flow will be developed in this project and it can simulate accurately the flow inception of cavitation bubble and growth as well as collapse in high-speed flows. With above study, the mathematical and physical models are combined to explain evolution of cavitation bubble and produced high-pressure on wall when it collapses. Furthermore, the effect of turbulence on this process will be studied in detail. Moreover, in view of following four aspects: air content in cavitation bubble, aeration concentration in flow, size distribution of air bubbles, relative position of air bubble, the interaction of air and cavitation bubbles will be studied using the developed mathematical model. This study will reveal the effect of aeration bubble on evolution of cavitation bubble in near-wall region and high-pressure acting on wall, thus this effect of aeration will be quantified and this study will be used to guide the engineering application.

掺气已经成为解决高速下泄水流中空蚀问题最经济和最有效的措施，但是目前对于掺气减蚀的机理认识还比较模糊，缺乏明确的理论。针对这个学科难题，本课题以减压水洞为实验平台构建一套同步测量空化泡形态、壁面压力和空化噪声的实验测试系统；同时，基于格子Boltzmann方法兼具微观特性和介观背景，算法简单，易于并行，边界条件容易实现, 可自动追踪各相界面的优势，开发一套能够准确模拟高速水流中空化泡初生、生长和溃灭的数学模型。在此基础上，联合运用实验手段和数值模拟来解释空化泡的演化过程和溃灭时对壁面产生的超高压分布，并进一步研究水流紊动对这一过程的详细影响。最后，采用开发的数学模型从空化泡含气量、空气泡浓度和级配分布、空气泡与空化泡相对位置这四个方面研究空气泡与空化泡的相互作用机制，从而揭示掺气泡对近壁区空化泡演化及壁面高压的抑制作用并量化掺气的效果，进而指导工程应用。

本项目开发了一套基于格子 Boltzmann伪势模型并耦合C-S和P-R状态方程的多相流模型。这套模型包括单松弛时间模型（LBM-BGK）和多松弛时间模型（LBM-MRT），同时包含二维和并行的三维计算模型，这套模型可以准确模拟空化泡的溃灭过程。采用单松弛时间伪势模型对单空化泡在平直壁面、垂直壁面、平行壁面之间的溃灭规律，双空化泡在平直壁面近壁区和远壁区溃灭规律研究进行了详细的研究；采用多松弛时间伪势模型对空化泡在V型壁面近壁区的溃灭规律（包括单个空化、横向和竖向双空化泡、竖向三空化泡）及壁面角度对空化泡溃灭规律的影响进行了详细研究；采用LBM-MRT对凹型壁面近壁区空化泡的溃灭规律（包括单个空化泡，竖向和横向双空化泡，竖向三空化泡）进行了研究；然后把LBM-MRT两相流模型扩展到三维，模拟了周期边界下的三维空化泡的溃灭过程。在空化泡溃灭规律的研究中，重点研究了空化泡距边壁距离、初始的空化泡内外压差、空化泡之间距离对空化泡溃灭演化过程中的形态变化、溃灭时间、微射流、压力场的影响规律。本项目共发表15篇文章，其中包括13篇SCI和1篇EI文章，大部分研究成果正在积极整理和投稿中。