复杂多相空泡流的数值模拟方法研究

发布时间：2018-04-05 00:19

本文选题：多相空泡流　切入点：数值模拟方法　出处：《上海交通大学》2013年博士论文

【摘要】：近年来，水下航行体超空泡减阻概念的提出，使得空泡流的研究成为水动力学领域的重要课题。当水下航行体被包裹在超空泡中运动时，能够大大减小其受到的阻力，从而极大地提高其在水中运动的极限速度。从技术方面来说，通气使水中航行体容易在较低的速度下实现超空泡状态；在实际应用中，通气也可作为自然空泡的一种辅助方式用于控制空泡的形态特性和水动力特性。此时，航行体周围充满水、蒸汽和不可凝结气体，介质在物体表面发生相变、掺混，气泡的发展和蒸汽空化之间互相影响，形成了非常复杂的多相空泡湍流流动。本文的研究目的就是建立能够准确描述这一物理现象的数学模型与精确、高效的数值计算方法，开发具有自主知识产权的计算软件，探索气、汽、液多相空泡流的流动特性及其机理，为试验研究和工程应用提供有益的理论依据和技术手段。本文主要研究内容和创新性成果如下：（1）从求解全流场RANS方程入手，构建了基于均质平衡流假设的气、汽、液多相空泡流动的数学模型，引入四种输运方程类空化模型和六种涡粘性湍流模式，以量化汽-液相变与湍流影响。建立了基于有限体积法与SIMPLE算法的数值计算方法，引入了多个高阶及高精度离散格式，，解决对流项所引起的稳定性与数值扩散等问题，提高了计算精度，能更好地捕捉空泡界面两侧物理量存在大梯度的特性。（2）自主研发了非定常多相空泡湍流流动的三维计算程序，对于复杂计算域和物理模型具有良好的适用性和计算效率。程序拥有多种边界设置，多种空化模型和湍流模式可供选择；根据输入的网格文件及边界条件，通过组合应用不同的程序模块，可以计算二维及三维通气或气、汽、液多相空泡湍流流动。并可通过自编的接口程序，引入GAMBIT生成的网格，实现了前处理过程的界面化。（3）研究了水槽中楔形翼上的基通气空泡流动特性。计算得到的通气空泡的单波波动流态与试验现象相符。计算结果表明：给定来流条件下存在空泡发生波动的临界通气率，通气空泡波动时其形态、泄气模式与泡内压力均呈现周期性变化，剧烈的空泡表面波动会导致空泡后部的断裂与脱落。相同通气率下，浸深的增加会导致平均空泡长度的增大与波动频率变小。（4）研究了绕水下航行体的气、汽、液空泡流动特性。给出了通气率、自然空化数与通气空化数、空泡尺度和阻力系数的相关性，分析了蒸汽空化和通气空化之间的相互影响。计算结果表明：通气过程引起蒸汽空化的减弱与溃灭，蒸汽空泡的溃灭导致局部流场内的压力振荡及压力波的传播；通气率较小时气体在蒸汽空泡表面的边界层内被主流夹带向下游迁移，并在没有蒸汽空泡的区域汇集，在空泡尾部形成泄气。
[Abstract]:In recent years, the concept of supercavitation drag reduction of underwater vehicle has been put forward, which makes the study of cavitation flow become an important subject in hydrodynamics.When the underwater vehicle is wrapped in a supercavitation, it can greatly reduce the resistance of the underwater vehicle, thus greatly increasing the limit speed of the underwater vehicle movement in the water.From the technical point of view, aeration can easily realize supercavitation at low velocity, and it can also be used as an auxiliary way to control the morphology and hydrodynamic characteristics of cavitation in practical applications.At this time, the navigation body is filled with water, steam and non-condensable gas, the medium phase transition on the surface of the object, mixing, the development of bubbles and steam cavitation interact with each other, forming a very complex multi-phase cavitation turbulent flow.The purpose of this paper is to establish a mathematical model that can accurately describe this physical phenomenon and an accurate and efficient numerical calculation method, to develop a calculation software with independent intellectual property rights, and to explore gas and steam.The flow characteristics and mechanism of liquid multiphase cavitation flow provide useful theoretical basis and technical means for experimental research and engineering application.The main contents and innovative results of this paper are as follows:1) based on the assumption of homogeneous equilibrium flow, a mathematical model of gas, vapor and liquid multiphase cavitation flow is constructed by solving the RANS equation of the whole flow field. Four kinds of cavitation models of transport equations and six kinds of vortex-viscous turbulence models are introduced.The effects of vapor-liquid phase variation and turbulence are quantified.The numerical calculation method based on finite volume method and SIMPLE algorithm is established. Several high order and high precision discrete schemes are introduced to solve the problems of stability and numerical diffusion caused by the convection term, and the calculation accuracy is improved.It can better capture the large gradient of the physical quantities on both sides of the cavitation interface.2) A 3D program for unsteady multiphase cavitation turbulent flow has been developed, which has good applicability and efficiency for complex computational domain and physical model.The program has a variety of boundary settings, a variety of cavitation models and turbulence models to choose from. According to the input grid files and boundary conditions, different program modules can be combined to calculate two-dimensional and three-dimensional ventilation or gas, steam, etc.Liquid multiphase cavitation turbulent flow.The interface of preprocessing process can be realized by introducing the mesh generated by GAMBIT through the interface program made by ourselves.The flow characteristics of base aerated cavitation on wedge-shaped airfoil in the flume are studied.The calculated single wave wave flow pattern of the aerated cavitation is in agreement with the experimental phenomena.The calculated results show that the critical ventilation rate of cavitation fluctuates under the given flow conditions, and its morphology, discharge mode and pressure in the bubble vary periodically when the cavitation fluctuates.Violent fluctuations in the surface of the cavitation can lead to the fracture and shedding of the posterior part of the cavitation.Under the same ventilation rate, the increase of immersion depth will result in the increase of average cavitation length and the decrease of fluctuation frequency.The flow characteristics of gas, steam and liquid bubble around underwater vehicle are studied.The correlation between aeration rate, natural cavitation number and aeration cavitation number, cavitation size and drag coefficient is given, and the interaction between steam cavitation and aeration cavitation is analyzed.The results show that steam cavitation decreases and collapses during aeration, and the collapse of steam bubbles leads to pressure oscillation and pressure wave propagation in local flow field.When the aeration rate is small, the gas is entrapped downstream in the boundary layer on the surface of the steam bubble, and then accumulates in the region where there is no steam cavitation, and the gas is deflated at the tail of the cavitation.
【学位授予单位】：上海交通大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：O35

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