近物面剪切流中空泡群运动与载荷特性研究

Cavitation bubbles appear near the interface between fluid and structure under the working condition of devices like propellers. They will seriously reduce the hydrodynamic performance of the device, and will cause structural vibration, surface material erosion and serious noise pollution. Different from the single bubble explosion, the bubble cluster explosion has the characteristics of strong jet interference. The inward concave angle jets will be induced by the outer bubbles, and the induced shock waves will spread in the cloud. Finally, the shock waves will get together in the cloud center and make lager noise and damage. The bubble motion and load characteristics are not only related to itself properties like bubble size and distribution, but also related to the flow structure and solid boundary features. A complex gas-liquid-solid coupling system is formed, which contains the strong discontinuity and large deformation questions. For the traditional Finite Element and Boundary Element methods, it is a quite difficult challenge. Therefore, based on the viscous flow and the multiphase flow theories, the following work is developed using the lattice Boltzmann method: a coupling dynamic model between cavitation bubbles and structures in shear flows is established on the mesoscopic scale; Study on shock waves propagation within the bubble cluster and its effect on bubble jet interference characteristics in free field; the study on bubble cluster collapse mechanism and its motion and load characteristics under the influence of shear flow and solid surface; the experimental research on bubble cluster dynamic characteristics.

舰船推进器等水中设备工作时，流场与结构耦合界面附近产生空泡群，影响设备水力学性能，其溃灭会造成结构振动、表面材料剥蚀及严重的噪声污染。空泡群溃灭特性不同于单个空泡溃灭，具有强烈的射流干涉特性，外围空泡会形成向内的凹角射流，向泡群内传播冲击波，在泡群中心处聚集，增强与泡群相关的噪声和破坏潜能。该过程中空泡群运动与载荷特性不仅与空泡尺寸、分布规律等泡群自身属性有关，而且与流场结构和物面特征等密切相关。由此形成气液固三相耦合的复杂系统，存在强间断、大变形等强非线性问题，传统有限元、边界元在求解该问题时均面临巨大挑战。为此，基于粘性流体和多相流理论，利用格子Boltzmann方法，开展以下工作：建立介观尺度上剪切流中空泡群与结构的耦合动力学模型；自由场中泡群内冲击波传播规律及其对空泡群射流干涉特性的影响研究；剪切流场和物面特征影响下空泡群溃灭机制及其运动、载荷特性研究；空泡群动态特性实验方案研究。

空泡群的存在不仅会影响螺旋桨等设备的水力性能。群溃灭特性还会造成结构的损毁，导致舰船、潜艇以 及鱼雷等设备的尾部结构强烈振动，产生空化噪声，降低水下设备的隐身性。空泡群内空泡与空泡之间会出现强烈的耦合过程，空泡间的相互作用以及溃灭产生的冲击波会造成空泡群内射流干涉，影响空泡的运动和溃灭特性，形成破碎、断裂等现象，涉及到多界面、 强间断、大变形等强非线性问题。. 首先，针对多气泡剪切流场，利用格子Boltzmann方法开展相关研究，通过多尺度展开能够得到宏观Navier-Stokes方程，在格子 Boltzmann 方法 Shan-Chen 多相流模型的基础上，引入空化模型，实现对空泡界面运动、大变形和破碎行为的捕捉，建立粘性流场中三维空泡群动力学分析模型。. 其次，以此为基础，联合浸没边界法处理流固耦合界面，进一步构建了针对剪切流中物面附近空泡群运动的气液固三相耦合动力学模型。同时合理的运用耦合的欧拉拉格朗日方法进行验证和计算。. 最后，在已有电火花空泡实验方法的基础上，通过设计并发电路，并改变每条电路中生成空泡的分压强度，开发包含多个、尺寸不同空泡的空泡阵列发生装置，并配合高速摄影技术，开展了水下空泡群动态特性实验研究。. 本项目为近场水下爆炸对舰船结构的毁伤机理研究提供理论参考和基础支持。