基于均质流理论的非定常空化流动及空蚀数值预测研究

发布时间：2021-10-28 15:53

　　本文基于均质混合流假设,通过考虑空穴溃灭过程释放的能量,提出了一种新的空蚀模型,为水力机械安全、稳定运行提供了重要的理论支撑。人们以往采用商用软件与实验结合的方法研究空化与空蚀机理。已有的数值模拟结果表明,虽然非定常空化现象可以较好地再现,但对空蚀只能作定性预测,且计算的空蚀区域与实际存在偏差,其原因是没有考虑含气率对空蚀的影响。在均质混合流假设的基础上考虑含气率时,首先是要优化非定常片空化的数值模拟方法。凝结和蒸发过程的非对称性是空化-空蚀的一个重要因素。因此,本文提出了改进的Zwart-Gerber-Belamri（Z-G-B）模型,并将C++语言嵌入到OpenFOAM作为新求解器。其次,为了避免质量传输和亚格子应力模型之间的显式耦合,采用了隐式大涡模拟来计算强湍流。通过对绕NACA0015、NACA66以及凸平面水翼的空化湍流进行模拟分析,再现了前缘附着空泡、回射流、空化脱落、空泡分离和空泡溃灭,预测的斯特劳哈尔数接近0.2,与实验结果吻合良好,证实本文提出的方法可以较好地预测空化现象。此外,用CFL条件数控制时间步长,避免了因网格尺度和信息传输与预测速度之间的差异而造成的浮点异... 

【文章来源】：清华大学北京市 211工程院校 985工程院校 教育部直属院校

【文章页数】：151 页

【学位级别】：博士

【文章目录】：
摘要
Abstract
Nomenclature
Chapter 1 Introduction
    1.1 Background
    1.2 Literature review
        1.2.1 Cavitation erosion prediction using CFD
        1.2.2 Free software
    1.3 Objectives
    1.4 Main contents of the dissertation
Chapter 2 Numerical modeling methods used for cavitating turbulent flow simula-tions
    2.1 Homogeneous mixture flow assumption
    2.2 Cavitation models
        2.2.1 Kunz model
        2.2.2 Schnerr-Sauer model
        2.2.3 Zwart-Gerber-Belamri model
    2.3 Turbulence modeling methods
    2.4 OpenFOAM
        2.4.1 OpenFOAM set up
        2.4.2 Volume-of-Fluid
        2.4.3 Grid mesh
    2.5 Summary
Chapter 3 Numerical analyses for cavitating turbulent flows around hydrofoils
    3.1 Partial cavitation over NACA0015 hydrofoil
        3.1.1 Hydrofoil geometry
        3.1.2 Mesh generation
        3.1.3 Computation setup
        3.1.4 Python image processing
        3.1.5 Results and discussions
    3.2 Unsteady partial cavitation around a plane-convex hydrofoil
        3.2.1 Hydrofoil geometry and computational domain
        3.2.2 Mesh generation
        3.2.3 Boundary conditions
        3.2.4 Results and discussions
        3.2.5 Comparison for ILES and ELES
    3.3 Unsteady cavitation around a NACA66 hydrofoil using dynamic time step
        3.3.1 Variable time step
        3.3.2 The total vapor volume
        3.3.3 Hydrofoil geometry, mesh generation and boundary conditions
        3.3.4 Results and discussions
    3.4 Summary
Chapter 4 Cavitation erosion prediction using CFD
    4.1 Erosion model
        4.1.1 Microjet assumption
        4.1.2 Flow aggressiveness and material damage
    4.2 Numerical prediction of cavitation-erosion on a NACA66 hydrofoil and aplane-convex hydrofoil with a semi-circular obstacle
        4.2.1 Computational domains
        4.2.2 Mesh generation
        4.2.3 Boundary conditions
        4.2.4 Results and Discussions
    4.3 Numerical prediction of cavitation-erosion on axisymmetric nozzle
        4.3.1 Computational domain
        4.3.2 Mesh generation
        4.3.3 Results and discussions
    4.4 Numerical prediction of the affected region by unsteady cavitating flow fora NACA0015
        4.4.1 Mesh generation and boundary conditions
        4.4.2 Results and discussions
    4.5 Summary
Chapter 5 Conclusions and future work
    5.1 Main concluding remarks
    5.2 Innovation points
    5.3 Future work
References
致谢
Appendix A Mesh analysis for NACA0015
    A.1 Cavitating Flow Simulation with Mesh Development using Salome OpenSource Software
Appendix B Developed software for the study case of NACA0015
    B.1 Python processing image algorithm
    B.2 Code of the pressure fluctuation plot at x/c = 0.2
Appendix C Developed software for the study case of a plane-convex hydrofoil
    C.1 Zwart-Gerber-Belamri cavitation model
    C.2 Code for plotting Cpand α
Appendix D Developed software for the study case of a NACA66 hydrofoil usingvariable time step
    D.1 NACA66 hydrofoil
    D.2 FFT program
Appendix E Cavitation erosion model: mesh and programs
    E.1 The mesh of the plane-convex hydrofoil with semicircular obstacle
    E.2 Program for the total vapor volume
    E.3 Developed software for the implementation of the cavitation-erosion model
    E.4 Gnuplot code for residuals
Resume and published papers


【参考文献】：
期刊论文
[1]Implicit large eddy simulation of unsteady cloud cavitation around a plane-convex hydrofoil[J]. HIDALGO Victor,罗先武,ESCALER Xavier,季斌,AGUINAGA Alvaro.  Journal of Hydrodynamics. 2015(06)
[2]A cavitation aggressiveness index within the Reynolds averaged Navier Stokes methodology for cavitating flows[J]. KOUKOUVINIS P.,BERGELES G.,GAVAISES M..  Journal of Hydrodynamics. 2015(04)
[3]Numerical study of unsteady cavitation on 2D NACA0015 hydrofoil using free/open source software[J]. Victor Hidalgo,Xianwu Luo,Bin Ji,Alvaro Aguinaga.  Chinese Science Bulletin. 2014(26)
[4]PARTIALLY AVERAGED NAVIER-STOKES METHOD FOR TIME-DEPENDENT TURBULENT CAVITATING FLOWS[J]. HUANG Biao,WANG Guo-yu School of Vehicle and Transportation Engineering,Beijing Institute of Technology,Beijing 100081,China.  Journal of Hydrodynamics. 2011(01)



本文编号：3463023