近壁空化泡溃灭的数值模拟

发布时间：2018-04-06 00:07

本文选题：空化泡　切入点：壁面　出处：《浙江大学》2015年硕士论文

【摘要】：空化现象普遍存在于各种水利机械中,它是一种包含大量气(汽)泡的多尺度的复杂的两相流动。气核和空化泡尺寸在微米-毫米量级,空化云团在毫米量级,然而空化流在米的量级。从微观方面看,各种空化类型的本质都是单个空化泡的集合体,想从宏观方面了解、控制和抑制空化的发生,我们必须从微观角度加深理解。本文采用直接数值模拟方法对近壁1个空化泡和27个空化泡的溃灭过程进行了研究。在研究1个空化泡溃灭过程中,研究的对象为纯含气型空化泡和纯蒸汽泡,两种空泡模型都表明：空化泡是以“心”型发生溃灭,在溃灭过程中形成高速微射流,溃灭瞬间作用在壁面上的作用力最大,因此此时对壁面的剥蚀作用也最大；无量纲距离γ越大,空化泡与壁面的相互作用力越弱,对壁面产生的作用力越小,溃灭的延长因子κ越小；作用在壁面上的压强和空化泡的尺寸没有关系,而与空化泡距壁面的无量纲距离γ有关；在无量纲距离γ一定的情况下,作用在壁面上的溃灭压强与驱动压强之间具有强烈的依赖关系。分析了27个纯蒸汽泡的近壁溃灭过程,研究发现：泡间相互作用以及壁面效应对泡群的溃灭过程具有显著影响,泡群整体上呈现出一种逐层溃灭的形态,当最后一个空化泡溃灭时,壁面上的冲击压强瞬间达到最大；无量纲距离和泡群密集度都对壁面冲击力存在影响,其中壁面距离影响更为明显一些；与1个空化泡相比,27个空化泡溃灭瞬间作用在壁面上的冲击力更大；壁面冲击力以压力波的形式在流场中传播,其传播速度约等于声音在水中的传播速度；在无量纲距离一定的情况下,溃灭压强是驱动压强平方根的线性函数。
[Abstract]:Cavitation is a complex, multi-scale two-phase flow that contains a large number of gas (vapor) bubbles in a variety of hydraulic machinery.The size of the gas core and cavitation bubble is in the order of micron-millimeter, the cavitation cloud is in the order of millimeter, but the cavitation flow is in the order of meter.From the microscopic point of view, the essence of all kinds of cavitation types is a single cavitation bubble. If we want to understand, control and restrain the occurrence of cavitation from the macroscopic aspect, we must deepen our understanding from the microscopic point of view.In this paper, the collapse process of 1 cavitation bubble and 27 cavitation bubbles near the wall is studied by means of direct numerical simulation.In the process of a cavitation bubble collapse, the pure gas-containing cavitation bubble and the pure steam bubble are studied. Both models show that the cavitation bubble collapses in the "heart" type, and a high-speed micro-jet is formed in the process of collapse.The interaction force between cavitation bubble and wall is weaker and the force on wall is smaller, the larger the dimensionless distance 纬, the weaker the interaction force between cavitation bubble and wall, and the larger the dimensionless distance 纬 is, the weaker the interaction between cavitation bubble and wall is.The smaller the collapsing extension factor 魏 is, the less the pressure acting on the wall is related to the size of the cavitation bubble, but the dimensionless distance 纬 from the cavitation bubble to the wall, and when the dimensionless distance 纬 is constant,The collapsing pressure acting on the wall has a strong dependence on the driving pressure.The near wall collapse process of 27 pure steam bubbles was analyzed. It was found that the interbubble interaction and wall effect had a significant effect on the collapse process of the bubble group, and the bubble group as a whole presented a layer by layer collapse pattern.When the last cavitation bubble collapses, the impact pressure on the wall reaches the maximum instantly, and the dimensionless distance and bubble group density both affect the wall impact force, in which the wall distance is more obvious.Compared with one cavitation bubble, 27 cavitation bubbles have greater impact force on the wall at the instant of collapse, and the wall impact force propagates in the flow field in the form of pressure wave, and its propagation velocity is about the same as the sound propagation velocity in the water.The collapse pressure is the linear function of driving the square root of the pressure under the condition of the dimensionless distance.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O35

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