Abstract
Within this study the influence of the interface description for partitioned Fluid–Structure Interaction (FSI) simulations is systematically evaluated. In particular, a Non-Uniform Rational B-Spline (NURBS)-based isogeometric mortar method is elaborated which enables the transfer of fields defined on low-order and isogeometric representations of the interface along which the FSI constraints are defined. Moreover, the concept of the Exact Coupling Layer (ECL) using the proposed isogeometric mortar-based mapping method is presented. It allows for smoothing fields that are transferred between two standard low-order surface discretizations applying the exact interface description in terms of NURBS. This is especially important for highly turbulent flows, where the artificial roughness of the low-order faceted FSI interfaces results in spurious flow fields leading to inaccurate FSI solutions. The approach proposed is subsequently compared to the standard mortar-based mapping method for transferring fields between two low-order surface representations (finite volume method for the fluid and finite element method for the structure) and validated on a simple lid-driven cavity FSI benchmark. Then, the physically motivated 3D example of the turbulent flow around a membranous hemisphere (Wood et al., 2016) is considered. Its behavior is predicted by combining the large-eddy simulation technique with the isogeometric analysis to demonstrate the usefulness of the isogeometric mortar-based mapping method for real-world FSI applications. Additionally, the test case of a bluff body significantly deformed in an eigenmode shape of the aforementioned hemisphere is used. For this purpose, both “standard” low-order finite element discretizations and a smooth IGA-based description of the structural surface are considered. This deformation is transferred to the fluid FSI interface and the influence of the interface description on the fluid flow is analyzed. Finally, the computational costs related to the presented methodology are evaluated. The results suggest that the proposed methodology can effectively improve the overall FSI behavior with minimal effort by considering the exact geometry description based on the Computer-Aided Design (CAD) model of the FSI interface.
Highlights
Fluid–Structure Interaction (FSI) simulations play an important role in modern engineering for the accurate prediction of phenomena which govern the mutual interaction between a fluid flow and a flexible structure
To allow the coupling between structures discretized using Isogeometric analysis (IGA) and fluid flows discretized with the finite volume scheme, an isogeometric mortar-based mapping method is elaborated and evaluated in the present study
It enables FSI simulations with isogeometrically discretized structures and a smooth representation of the FSI interface
Summary
Fluid–Structure Interaction (FSI) simulations play an important role in modern engineering for the accurate prediction of phenomena which govern the mutual interaction between a fluid flow and a flexible structure. The iterative Gauss–Seidel partitioned approach (Sicklinger, 2014; Sicklinger et al, 2014) is used for the FSI simulation, which is known as serial staggered procedure with an iterative correction loop (Felippa and Park, 1980) It allows for a highly modular framework within which various fluid or structural solvers can be employed, whereas the fulfillment of the interface constraints is obtained in an iterative manner. Schemes have to be developed which allow the transformation of interface fields, for instance structural displacements and fluid tractions, across the common interface with minimal error These methods comprise the nearest neighbor method, the nearest element interpolation, the barycentric interpolation and the mortar method amongst others (see Park et al (2002), de Boer et al (2007, 2008) and Wang (2016) for more details). Kinks on the surface due to a coarse finite element resolution on the structural side may lead to artificial shifts in separation and reattachment points which substantially influence the flow development and which in turn can cause the evolution of inaccurate deformation patterns due to the coupling
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