结构物砰击入水过程的CFD-DEM-IBM数值仿真

Numerical simulation of the water slamming process by the CFD-DEM-IBM approach

摘要:

为实现入水过程的精细数值仿真,解决入水问题数值模拟所面临的关键技术问题,围绕结构入水过程中固体移动边界的合理描述、自由液面的准确捕捉及流固耦合作用的精细刻画等核心难题,融合计算流体动力学-离散单元法（CFD-DEM）、浸入边界法（IBM）及改进的守恒式Level Set（ICLS）方法,提出了一种CFD-DEM-IBM方法。采用固定的笛卡尔网格离散计算域,分别通过CFD与DEM描述流体与结构运动,引入IBM追踪固体移动边界并获取准确的流固耦合作用力,采用ICLS方法在保证守恒性的同时隐式捕捉自由液面,并通过分区算法,在一个时间步内进行数次交错迭代以反映流固两相间的强耦合效应,建立了高解析度的CFD-DEM-IBM数值模型。通过圆柱常速入水、楔形体对称及非对称入水和多体入水现象仿真分析研究,结果表明,CFD-DEM-IBM方法能够考虑多块体间的相互作用,在准确反映流固耦合效应的同时能够获得高解析度的流场,在多体入水问题处理方面优势显著。

Abstract:

To overcome the significant challenges to accurate numerical simulations of water entry problems, like the treatment of the moving boundaries, the description of highly distorting free water surface and the reflection of strong coupling effect between fluid and solids, a CFD-DEM-IBM approach, which incorporates the computational fluid dynamics-discrete element method (CFD-DEM), the immersed boundary method (IBM) and the improved conservation level set (ICLS) method, is proposed for the precise prediction of water entry phenomenon. Fixed Cartesian grids are used to discretize the computational domain, with CFD and DEM used to describe the motion of fluid and the motion of solid bodies, respectively. IBM is introduced to track the solid boundaries and obtain accurate fluid-solid interaction forces. The free water surface is captured using the ICLS method which can ensure both the validity of interface properties and the conservation of mass. A partitioning algorithm is employed to perform multiple alternating iterations within a time step to reflect the strong coupling effect between fluid and solid, establishing a high-resolution CFD-DEM-IBM numerical model. Water entry of a cylinder with prescribed motion, symmetric and asymmetric water entry of a wedge and water entry of multiple bodies are then performed. The results show that the detailed resolution of the fluid phase along with the strong coupling effect can be reasonably reflected by the CFD-DEM-IBM approach, and it is remarkable in addressing water entry problems even when multiple rigid bodies are involved.