A novel overset grid assembly strategy based on immersed boundary method for fluid-structure interaction

Abstract

The overset grid method and the immersed boundary (IB) method, which have significant advantages in dealing with moving boundaries involving large amplitude motion, are widely used for fluid-structure interaction (FSI) problems in engineering applications. However, these methods still have some limitations. In the overset grid method, the hole-cutting operator and iterative procedure, which are complex and time-consuming, are necessary for flow field information exchange between the sub-domains and the background domain. In the IB method, non-physical pressure oscillations, which can result in numerical instability, often exist in simulating FSI problems with moving boundaries. In order to integrate the advantages of these two methods and overcome their limitations, a novel overset grid assembly strategy based on the IB method is proposed. In the present method, two additional body force terms, obtained by the diffuse-interface IB method, are considered in the momentum equations for solving the flow field in the background domain. The first body force term implicitly imposes a no-slip boundary condition of the body surface in the background domain. The second body force term is used to further correct the background flow field, and to ensure the continuity of the flow field between the background domain and the sub-domains. In this way, the explicit flow field information interpolation process from the sub-domains to the background domain is not necessary. Therefore, the complicated hole-cutting operator can be avoided. In addition, a third-order polynomial time extrapolation technique is adopted to estimate the pressure at the sub-domain boundaries. The velocity at the sub-domain boundaries can be determined with the estimated pressure. Therefore, the velocity and pressure boundary conditions at the sub-domain boundaries can be ensured without an iterative process between the sub-domains and the background domain. It significantly enhances the computational efficiency since the iterative process is avoided. Several benchmark cases are carried out to verify and validate the novel overset grid assembly strategy. In all cases, the results are in good agreement with the published experimental or numerical results. Furthermore, the results demonstrate that the present method can effectively suppress non-physical pressure oscillations, which often exist in the IB method when considering moving boundaries.