基于直角网格法的单个和阵列布置下柔性水翼绕流数值模拟

研究柔性水翼在不可压缩流体中的水动力特性,对于船舵和减摇鳍等海洋结构物的设计和性能优化具有重要意义.本文将自主开发的径向基函数虚拟网格法求解器扩展到模拟绕单个或多个柔性水翼的不可压缩流动问题.数值模型基于虚拟网格有限差分法考虑浸入边界对流场的影响,引入紧支径向基函数(compact supported radial basis function,CSRBF)以物面Lagrangian质点追踪复杂的柔性动边界.基于该方法,首先模拟了均匀流中主动拍动的柔性水翼,升阻力系数良好的网格收敛性结果验证了本文方法的精度和可靠性.并研究了柔性水翼在不同振荡频率下的水动力特性,阐述了柔性水翼的推力生成机制.然后模拟了绕阵列布置柔性水翼的流动现象,研究了不同间距和不同振荡频率下水翼表面的升阻力系数变化规律和尾涡特性,观察到紧密布置的柔性水翼在高频振荡下推力系数存在显著的放大效应,同时推力为零时的临界频率提前.

Numerical simulation of flows around single and multiple flexible hydrofoils in array arrangement by a Cartesian grid method

Studies on hydrodynamic characteristics of viscous incompressible flows around flexible hydrofoils are of practical importance for the design and performance optimization of marine structures such as ship rudders and stabilizing fins.The aim of this paper is to extend a radial basis function based ghost cell method to simulate flows around single or multiple flexible moving hydrofoils in array arrangement.The numerical model is based on a ghost cell finite difference method for considering the influence of the immersed boundaries on the flow.Also,a compact supported radial basis function(CSRBF)is introduced to track the complex flexible boundary with some controlling points of the body surface.Based on the present method,the uniform flow around a flexible hydrofoil swimming like a fish is simulated.Good grid convergence of drag and lift coefficients demonstrates the accuracy and reliability of the present method.Also,the hydrodynamics patterns of the flexible hydrofoil under different oscillation frequencies are studied.Further,the thrust generation mechanism of the hydrofoil is explained.Afterwards,flows around the undulating hydrofoils in array arrangement are simulated.The force coefficients and wake patterns under different distances and oscillation frequencies are investigated.It is observed that the thrust coefficients of the hydrofoils under narrow arrangement and high oscillation frequencies have significant amplification effects.In addition,the critical frequency at zero thrust reduces.