中文摘要：

为避免复杂贴体网格的生成，该文采用一种隐式直接力浸入边界法模拟复杂边界流动问题。借助求解不可压缩N-S方程组的分步投影方法的思想，来求解基于浸入边界法的耦合系统方程。其中固体边界离散点的作用力密度通过强制满足固体边界的无滑移条件导出，进而通过占光滑函数对固体壁面附近速度场进行二次修正。在空间离散上，对流项采用QUICK迎风格式，扩散项采用中心差分格式，采用二阶显式Adams-Bashforth法离散时间项。以雷诺数为25、40和300的圆柱绕流为基准数值算例，通过与实验结果和其他文献数值结果的对比，验证数值计算方法的可靠性。

英文摘要：

To avoid the traditional body-fitted numerical methods and extend the application of immersed boundary method to complex flow, a new numerical method for simulating complex flow based on the implicit direct force immersed boundary method is presented. A mathematical model described the interaction between an immersed rigid body and fluid is established and whose governing equation is solved using the projection step method similar to the fractional step method for solving the incompressible Navier-Stokes equation. The moment source is not pre-calculated, but determined implicitly in such a way that velocity at the immersed boundary interpolated from the corrected velocity field accurately satisfies the no-slip boundary condition. Also, the second velocity near the solid wall updated is implemented using a ~ smooth function. The QUICK upwind scheme and the second central scheme are applied to solve convection and diffusion terms respectively. The second explicit Adams-Bashforth method is used to the time discretization. The present immersed boundary method（IBM） is validated by the basic numerical example of flowing over one cylinder at Reynolds number 25,40 and 300.