IMECH-IR  > 流固耦合系统力学重点实验室
复杂壁面边界条件非定常空化流动特征研究
Alternative TitleUnsteady cavitating flow with complex wall boundary conditions
余超
Thesis Advisor王一伟
2018-06
Degree Grantor中国科学院大学
Place of Conferral北京
Subtype博士
Degree Discipline工程力学
Keyword非定常空化 复杂边界条件 流固耦合 Lesunsteady Cavitating Flow Complex Wall Boundary Conditions, Fluid-solid Coupling Les
Abstract

非定常空化流动一直是水动力学领域的热点,是具有重大工程应用背景的前沿基础问题。空化一直是影响水下发射等高速航行体载荷的控制主要因素之一,而空化引起的振动、噪声和空蚀等现象也在工程上备受关注。与当前大多数空化流动研究的楔形体、水翼等简单构型不同,实际工程问题中的空化通常发生在高速航行体或高速运转的水利机械部件附近,是包含复杂几何壁面、运动壁面或流固耦合壁面的复杂壁面边界条件空化流动,涉及到湍流、多相流、相变、复杂几何边界、流固耦合等多个难点,物理现象极为复杂,流动机理认识尚不够深入,值得进一步研究。

复杂几何壁面附近的旋涡结构与空泡相互作用,往往造成新的流动特征现象,其中规律研究不够充分透彻。进一步,考虑运动壁面的空化流动中旋涡结构和空泡演化规律更加复杂,实验观测以及数值模拟难度更大,导致精细研究成果较为缺乏。更进一步,考虑流固耦合壁面边界的空化流动,则由于空化流动不稳定性以及空泡溃灭引起的高频激励使得耦合作用规律复杂。虽然近些年日益受到关注,但相关研究尚处于初步阶段,空化流动与结构相互作用规律及其机理认识不够清晰,研究成果相对匮乏。本文通过对复杂几何壁面、运动壁面、流固耦合壁面三类复杂边界条件空化流动依次由浅到深进行机理研究,并总结特征规律从而系统地加深对复杂边界条件空化流动认识为解决空化流动相关工程问题提供基本依据。具体包括以下内容:

1)针对复杂几何壁面边界条件空化流动,本文进行了近壁面轴对称空化流动研究。基于SHPB发射系统进行了水下发射实验,发现了近壁面轴对称航行体空化流动的两种流型。通过开源软件OpenFOAM求解器interPhaseChangeFoam结合基于大涡模拟方法(large eddy simulation, LES)、VOFVolume of Fluid方法以及对蒸发和凝结相变过程进行数值模拟的传质空化模型,采用PISO算法求解不可压缩N-S方程,对实验中的非定常空化流动进行精细数值模拟结合实验和数值模拟对形成原因及演化机理进行分析,获得了近壁面强约束影响产生堵塞效应的特征规律,以及局部空泡脱落过程中回射流、空泡与旋涡运动相互作用的演化机理。

2)针对运动壁面边界空化流动,本文进一步展开了非均匀来流大侧斜螺旋桨非定常空化流动研究。在前述空化流动数值模拟方法基础上引入旋转动网格以及滑移面插值技术,将LES方法应用到螺旋桨空化数值模拟中,获得了较传统RANS方法更加精细的结果,捕捉到更多实的包括空泡初生以及梢涡空泡等流动细节特征。通过对数值模拟获得的详细流场结果进行分析,获得了空化数2.99条件下非均匀尾流中大侧斜螺旋桨空化主要控制因素,空泡演化与旋涡结构相互作用以及空泡演化与压力脉动影响规律特征。

3)流固耦合壁面边界条件空化流动方面,本文将空化流动与研究广泛的圆柱扰流涡激振动问题相结合,对空化流动中流固耦合特征规律进行研究。通过量纲分析获得了空化流动中圆柱涡激振动问题中的无量纲控制参数。基于OpenFOAM中采用PSIO算法的空化流动求解器,开发了采用弱耦合方法的高效率空化流动流固耦合数值模拟程序,对空化流动中圆柱涡激振动进行数值模拟研究;获得了空化流动中圆柱振动的主要无量纲控制参数作用规律;并通过空化与非空化流动中圆柱涡激振动数值模拟结果对比,获得了空化现象对涡激振动影响规律。

Other Abstract

Unsteady cavitating flow has always been discussed in the field of hydrodynamics. It is a frontier fundamental problem which can be applied in many engineering areas. Cavitation is one of the most important factors that affects the control of high-speed underwater launched vehicles. The phenomenon such as vibration, noise, and erosion caused by cavitation has also attracted attention in recent years. Unlike most simple configurations such as wedges and hydrofoil, which are currently studied in most cavitation flow studies, cavitation usually occurs near high-speed navigation bodies or high-speed hydraulic machinery components in practical engineering problems, including complex geometrical walls as well as moving wall surfaces. Complex problems are studied involves turbulence, multiphase flow, phase change, complex boundary conditions, fluid-solid coupling, etc. The physical phenomena are extremely complicated of unsteady cavitating flow, and we still lack the understanding of the flow mechanism. More in-depth study is needed in the future.

Interaction between the vortex structure and the cavitating flow around the vehicles with complex shape often leads to new flow characteristics, in which the study is not thorough enough. Besides, it is much more difficult for us to considering the vortex structure and the evolution of the cavitating flow around moving body. Both experimental methods and simulations of the problem are more difficult, resulting in a lack of research. Furthermore, the high-frequency excitation caused by the instability of the cavitating flow when considering the cavitating flow around the fluid-solid coupling wall make the problem more complicated. Although research in the area has gradually increased in recent years, related problems still need further in-depth research. The laws and mechanisms of the interaction between cavitating flow and complex structures are not clear, and the research results are relatively scarce. In this paper, we aim to study the mechanism of the cavitating flow around various underwater vehicles under the effect of three types of complex boundary conditions, which are vehicles with complex shape, moving wall and fluid-solid coupling wall. We will study the problem from the shallow to the deep, and summarize the characteristic rules, so as to systematically deepen the understanding of cavitation flow in complex boundary conditions. The study provides the basic basis for solving cavitation-related engineering problems. Specifically include the following problems:

(1) Cavitating flow around axisymmetric projectile near wall is studied in this paper to understand the mechanism of the cavitating flow around the vehicles with complex shape. Based on the Split Hopkinson Pressure Bar (SHPB) launch system, an underwater launched water tank experiment was conducted. Two types of flow patterns of the cavitating flow around axisymmetric bodies near wall were found. The interPhaseChangeFoam solver of the open source software OpenFOAM is used to do the simulation. Numerical methods include large eddy simulation method (LES), fluid volume method (VOF), mass transfer cavitation model for the evaporation and condensation phase transition process and pressure implicit with splitting of operators (PISO) algorithm to solve the incompressible NS equations are used here. By comparing the experimental data and simulated results, the mechanism of the cavity formation and evolution are analyzed. The characteristics of the blockage effect due to the strong confinement effect in the near wall are obtained, and the evolution mechanism of the interaction between the back jet, the vacuole and the vortex motion in the process of local cavitation.

(2) Unsteady cavitating flow around a highly skewed propeller in non-uniform wake is further studied which focusing on the cavitating flow around a moving wall boundary. On the basis of the aforementioned numerical methods, the rotating dynamic mesh method and sliding wall interpolation approach are introduced. A more accurate result than the traditional RANS method are obtained by applying the LES approach, which can capture the initial details of the incepted cavity and tip vortex cavity. Main control parameters of the cavitating flow around the highly skewed propeller in non-uniform wake are obtained by analyzing the simulated flow field results in details when the cavitation number is 2.99. The interactions between the cavity evolution and the vortex structure/ pressure pulsation are discussed.

(3) We combine the cavitating flow with the study of vortex-induced vibrations of a circular cylinder here to understand the mechanism of the cavitating flow around the fluid-solid coupling wall. The dimensionless control parameters of the aforementioned problem are obtained in this paper. Based on the cavitating flow solver PSIO algorithm in OpenFOAM, a high-efficiency fluid-solid coupled numerical simulation program using weak coupling method was developed to calculate the cavitation in a vortex-induced vibrations of circular cylinder problem. Regularity of the non-dimensional main control parameters of the cavitating flow are investigated. Moreover, the effect of cavitation on vortex-induced vibration are obtained by comparing the different simulated results of the vortex-induced vibrations of circular cylinder problem with and without cavitation.

Call NumberPhd2018-034
Language中文
Document Type学位论文
Identifierhttp://dspace.imech.ac.cn/handle/311007/78582
Collection流固耦合系统力学重点实验室
Recommended Citation
GB/T 7714
余超. 复杂壁面边界条件非定常空化流动特征研究[D]. 北京. 中国科学院大学,2018.
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