Design and implementation of Immersed Boundary Method with discrete forcing approach for boundary conditions

Jasak, Hrvoje and Rigler, Damir and Tuković, Željko (2014) Design and implementation of Immersed Boundary Method with discrete forcing approach for boundary conditions. = Design and implementation of Immersed Boundary Method with discrete forcing approach for boundary conditions. In: 11th. World Congress on Computational Mechanics - WCCM XI 5th. European Congress on Computational Mechanics - ECCM V 6th European Congress on Computational Fluid Dynamics - ECFD VI, 20-25.07.2014., Barcelona; Spain.

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This article describes design, implementation and validation of Immersed Boundary Method (IB) for finite volume based Computational Fluid Dynamics (CFD). In CFD, objects are usually described using body conformal meshes, where boundary conditions are imposed on the boundary faces of a mesh and provide the information necessary to properly describe object geometry and flow parameters. Generation of such meshes still requires some effort, even for simple geometries. If an object changes its position (or form) during time, mesh motion, or even topological changes of the mesh are required. Both require computational effort and can result in an unusable mesh. These obstacles can be avoided with an alternative approach: Immersed Boundary Method (IBM). IB method does not use a body-conformal mesh. Instead, background volume mesh is used for the flow domain together with a separate IB surface mesh for the object outline. Generation of the IB surface mesh is not related to the generation of the volume mesh making it significantly easier. As the object is not described using boundary faces, it is necessary to use a IB surface mesh for boundary condition imposition. The IB surface mesh is then immersed into the domain volume and the calculation matrix is modified to account for the object geometry. This enables very fast solutions for different geometries on the same background mesh. Furthermore, moving the IB surface mesh through the background mesh is significantly easier than any mesh-manipulation method. For this work IB method has been implemented into OpenFOAM using a discrete forcing approach, where discretized equations are only affected in the cells touching the IB (direct imposition of Boundary Conditions). Direct imposition of BC preserves sharpness of the object surface. Wall functions are used to allow high Reynolds number flows. Dirichlet and Neumann BC are implemented using quadratic interpolation, where unknown coefficients are determined using least square method on extended stencil 1. Implementation into OpenFOAM enables use of polyhedral background meshes and automatic mesh refinement. The IB method implementation is validated with four test cases that cover transient and steady-state, laminar and turbulent, single phase and free surface two-phase flow. Both integral values (such as force on the object) and certain fields (such as pressure, or free surface) are compared with experimental results from literature and show satisfactory agreement.

Item Type: Conference or Workshop Item (Lecture)
Keywords (Croatian): Boundary conditions; Computational mechanics; Dynamics; Fluid dynamics; Geometry; Least squares approximations; Mesh generation; Reynolds number; Turbulent flow; Two phase flow; Wall function; Automatic mesh refinements; Design and implementations; High Reynolds number flows; Immersed boundary; Immersed boundary methods; Method implementations; Quadratic interpolation; Validation; Computational fluid dynamics
Divisions: 500 Department of Energy, Power Engineering and Environment > 530 Chair of Turbomachinery
Indexed in Web of Science: No
Indexed in Current Contents: No
Citations SCOPUS: 0 (30.08.2017.)
Date Deposited: 01 Jun 2015 08:27
Last Modified: 30 Aug 2017 10:32

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