【作者】 向敏；

【导师】 张为华；

【作者基本信息】 国防科学技术大学 ， 航空宇航科学与技术， 2011， 博士

【摘要】 空泡减阻通过改变水下航行体表面介质属性和流场结构,可实现航行体减阻90%以上,是满足水下航行体高航速和远航程要求的革命性减阻技术。本文以超空泡航行体通气空泡流为研究对象,建立了大尺度和多尺度空泡流数值仿真模型,对通气空泡生长过程和多尺度空泡流与航行体间相互作用展开了系统深入的研究,揭示了多尺度空泡流减阻机理,为超空泡航行体设计提供了理论基础。分析了通气空泡形成过程中液体、连续气体及离散气泡间相互作用的物理过程,基于均质多相流模型,耦合自然空化模型和表面张力模型,建立了大尺度空化流仿真模型;分析了通气空泡尾部自由面掺气机理,建立了回射流掺气模型;基于欧拉-欧拉双流体模型,耦合两种群体平衡方法和回射流掺气模型,建立了多尺度空泡流仿真模型,为开展通气空泡流仿真研究提供了重要基础。应用多尺度空泡流仿真模型,开展了垂直管内通气空泡流仿真研究,得到垂直管内空泡尾部掺气率变化规律,准确预示了通气空泡下游回流区、过渡区和管流区流场结构,得到了不同区域内气泡体积含量、流体速度和气泡大小等参数演化规律,分析了液流速度、通气量、来流湍流度等对流场参数的影响,通过与试验数据对比,验证了回射流模型和多尺度空泡流模型正确性,为局部通气空泡流仿真提供了理论和方法基础。分别基于大尺度和多尺度空泡流模型开展了局部通气空泡流仿真研究,得到大尺度空泡形态随通气量变化规律,分析了不同工况下试验体后尾迹区流体速度、气泡体积含量和气泡大小等参数分布特性,得到了影响气泡流扩散方式和扩散速率的主要原因;分析了试验体表面边界层内参数分布特点,探讨了掺气率和航行攻角对微气泡流参数影响,揭示了局部通气空泡减阻机理,为空泡减阻技术发展提供了技术支撑。基于大尺度空泡流模型开展了高速航行体通气空化过程仿真研究,基于仿真结果建立了适用于多种泄气方式和大Froude数范围的空泡形态计算模型,通过与试验数据和仿真结果对比验证了模型准确性;提出了带进水管路航行体性能评价参数,基于自然空化过程仿真得到航行体水动力特性和摄水性随航行工况变化规律,分析了楔形尾翼对自然空泡形态和航行体水动力特性影响,为高速超空泡航行体设计提供了理论依据。本文研究成果将促进空泡减阻技术发展,推动多相流仿真技术进步,对超空泡航行体研制具有重要理论意义和工程应用价值。更多还原

【Abstract】 Drag reduction using cavitation, proposed as a revolutionary method to meet the demand of high speed and long voyage for the future underwater vehicles, is capable of achieving drag reduction over 90% by modifying the flow property and strucure near the vehicle surface. In this paper, the macroscale and multiscale simulation models were established for the ventilated cavitating flow. Systematical and deep research was carried out on the development process of the ventilated cavities, as well as on the interaction between the multiscale cavitating flow and the vehicle body, revealing the evolution process of the macroscale cavity and the dispersion characteristics of the microscale bubbles. The drag reduction mechanisms by the ventilated cavity were further explored, providing theoretical basis for the design of the supercavitating vehicles.The interaction between liquid, continuous gas and dispersed bubbles during the formation of the ventilated cavity was analyzed. The macroscale simulation model for the ventilated cavitating flow was complemented based on the homogeneous multiphase model, integrated with the natural cavitation model and the surface tension force model. The air entrainment model by the re-entrained jet was put forward based on the analysis of the air entrainment mechanisms for the free surface flows. Thereafter, the multiscasle simulation model for the ventilated cavitating flow was established based on the Euler-Euler two fluid model, incorperated with two types of population balance methods and the air entrainment model by the re-entrained jet. The proposed numerical models provide important basis for the numerical research on ventilated cavitating flows.Numerical research on the ventilated cavity in the verticle pipe was carried out using the multiscale simulation model. The variation of the air entrainment rate at the cavity tail was obtained. Three different regions downstream the ventilated cavity including the vortex region, transitional region and the pipe flow region were successfully predicted. The distribution characteristics of the flow field parameters such as the void fration, velocity and bubble size in different regions were obtained. The influence of liquid velocity, ventilation rate and inlet turbulence intensity on the flow field parameters were further discussed. Good agreement was observed between the simulation results and the experimental data, validating the proposed multiscale simulation model and the air entrainment model. The above research sets the theoretical and method basis for the simulation on ventilated partial cavity.Simulations for the ventilated partial cavity was accomplished based on the macroscale model and the multiscale model respectively. The evolution of the cavity shape along with the ventilation rate was successfully captured. The distributions of the flow field parameters including the void fraction, liquid velocity and bubble size in the wake region behind the test body were invesitgated, which revealed the critical elements to the change of the dispersion way and speed of the bubbles. The characteristics of the flow field in the boundary layer of the test body surface were explored. Furthermore, the influences of air entrainment rate and sailing attack angle on the microscale bubbly flow were studied. The drag reduction mechanisms by ventilated partial cavity were better understood, providing technical support for the development of drag reduction method using cavitation.Numerical research was carried out for the high-speed ventilated cavitating vehicles based on the macroscale simulation model. A mathematical model for calculating the cavity shape, applicable for the ventilated cavity with various gas-leakage mechanisms and wide range of Froude number was developed. The model was validated in comparison with the experimental and numerical data. The parameters to evaluate the cavitating vehicle with water inlet pipe were put forward. Subsequently, the performance for the cavitating vehicle with water inlet pipe under various sailing speed and attack angle was studied based on the simulation for the natural cavitating process. The interaction between wedge control fins and the natural cavity was investigated. Obtained results provides theoretical basis for the design of high-speed cavitating vehicles.The research achievements in the thesis will surely promote the development of drag reduction techniques using cavitation, as well as providing support for the advancement of the simulation techniques for the multiphase flows. The research will be of great theoretical value as well as engineering practice meaning for the future supercavitating vehicle research.更多还原