The fine resolution of the boundary layer is necessary to correctly predict the viscous and pressure forces which are later use to displace the sphere in the domain. The mesh around the sphere was generated with snappyHexMesh adding a few layers close to the wall. The figures show a slice through the mid plane of the mesh.

Figures to the right show the two meshes generated for the sphere (on the left) and for the background mesh (on the right). In this case the extension of the domain is obvious since the experimental setting is bounded by six walls. In this section the set up of the simulation is shown step by step and the choice of the parameters employed is tried to be justified whenever it is possible.Īs in every CFD simulation the first step is to decide the domain extension and how to generate an adequate mesh which guarantees a desired solution quality. The setup can be seen in the figure to the right. The same can be done here if other Re-numbers have to be simulated. The variation of the Re-number in the experiments was achieved by choosing fluids with different fluid viscosities μ_f. For this tutorial the lowest Re number was chosen. Different Re-numbers based on the free falling velocity were measured (Re: 1.4, 4.1, 11.6 and 32.2). The sphere had a diameter of 15mm and a density ρ_s of 1120 kg/m^3. The lower part of the sphere was hanging 120mm from the bottom wall. The experimental settings consists in a rectangular box with dimensions of 100x100x160mm (in x-,y- and z-coordinate direction). The uncertainty of a tool is connected to the risk not meeting a design criteria when this tool is employed in an industrial context.įor this purpose the experimental setting by was chosen to be simulated. This is a mandatory step to estimate the uncertainty of a given simulation method.

The second objective is to validate the overset methodology implemented into OpenFOAM with experiments.

The different mesh regions are usually not subject to topological changes which allows to maintain the original mesh quality. Inside each disconnected mesh region, the solution is calculated by means of the usual finite volume discretisation. In order to couple the disconnected mesh regions, the flow variables are interpolated between the meshes. It consists in a fixed background mesh and one or more disconnected mesh regions which are subject to large displacements. The overset methods (also know as chimera method) is very useful if large body motions have to be simulated.

The first objective is to show how to set up an overset simulation with OpenFOAM.

Sphere michael