航行体出水仿真的自适应网格技术研究

Research on Adaptive Grid Technology for Simulation of Vehicle Water Exit

摘要:

研究航行体跨界质过程中周围流场的演变规律、航行体的流体力特性的响应机制对优化航行体设计、提高航行效率和延长使用寿命具有重要意义。本研究基于叉树数据结构，结合洞边界和流体体积模型 （Volume of Fluid，VOF）的体积分数梯度对笛卡尔网格进行自适应网格细化和粗化，解决了重叠网格方法中网格数量过多的问题。验证结果显示，在同等网格尺度及计算配置的情况下，采用自适应网格技术能够节省 64.59%的计算时间。在对航行体以不同初速度出水过程的参数化研究中，重叠网格方法用于离散有运动部件的计算域，VOF 多相流模型用于求解流体体积分数方程，有限体积方法（Finite Volume Method，FVM）用于对控制方程进行空间和时间离散，Realizable k-ε 湍流模型用于对湍流方程进行求解。参数化仿真结果表明： 自由液面效应和尾流拉曳断裂对航行体出水过程影响较大。初始航行速率越大，所受到的流体力就越大，航行体速率呈非线性下降。

Abstract:

The investigation into the evolution law of the surrounding flow field and the response mechanisms of the hydrodynamic characteristics of the vehicle during cross-medium navigation is of significant importance for optimizing vehicle design，enhancing navigational efficiency，and extending service life. Utilizing a quadtree data structure in conjunction with adaptive mesh refinement and coarsening based on hole boundaries and volume of fluid （VOF）gradient，the adaptive Cartesian grid employed in this study addresses the issue of excessive mesh count in overlapping grid methods. The verification results show that，under equivalent mesh scale and computational configuration，the adaptive mesh technology achieves a reduction of 64.59% in computational time. As for the numerical simulation of vehicle water exit at different initial velocities，the overlapping grid method is used to discretize the computing domain with moving parts，and the VOF multiphase flow model is adopted to solve the fluid volume fraction equation. The finite volume method（FVM）is utilized for spatial and temporal discretization of the governing equations. The turbulence model，Realizable k-ε，is employed for solving the turbulence equations. The numerical results indicate that the free-surface effect and wake entrainment/shedding significantly influence vehicle water exit. As the initial navigational velocity increases，the hydrodynamic forces acting on the vehicle intensify， resulting in a nonlinear decrease in vehicle velocity.