The descritization of the continous fluid is the essential task in the field of computational fluid dynamics and numerical analysis. Due to the stiff learning curve of OpenFOAM, especially at the beginning, even simple geometry meshing procedures are hard to achieve. Therefore, the following training case provides information for the first steps with snappyHexMesh.
The Surface Feature Refinement (SFR)
SnappyHexMesh can refine defined feature edges during the refinement stage. However, many people in the community have a lot of problems with the feature edge refinement strategy. Therefore, Holzmann CFD provides the SFR case which meshes a pipe with three different surface feature refinement set-up's. The results, especially the wrong ones, might be familiar.
Meshing a Pipe
People all over the world who start in the field of numerical simulation commonly start with a simple fluid dynamic analysis in a pipe. However, for new OpenFOAM users, even the trivial pipe meshing can be challenging. Therefore, Holzmann CFD provides two cases in which a pipe bending under 45 degree and 90 degrees will be discretized. Additionally, the layer generation is applied while a coverage of 99.5 percent is reached.
Meshing a Helix
The in-house mesher of OpenFOAM® named snappyHexMesh is infamous in the community due to meshing problems in more advanced and complex geometries. This might be true if you are not using snappyHexMesh correctly. This training case shows the basic meshing settings for the helix geometry. Additionally, a way of the layer generation is shown which will end up with a coverage above 95 percent.
The Magnus Effect
The investigation into different phenomena can be done easily with numerical analysis. Some of the most famous phenomena are already simulated by Holzmann CFD such as the Magnus Effect, the Taylor-Rayleigh instability or the Kelvin-Helmholtz instability. People who love soccer should be aware of the Magnus effect, as it is a very common phenomenon in this kind of sport. However, it is also necessary for golf, tennis, table-tennis and so on.
Pseudo-2D Adaptive Mesh Refinement
Adaptive mesh refinements (AMR) is a common strategy for large numerical cases including phenomena that have to be reasonably resolved (mesh density). Using the AMR functionality, OpenFOAM® allows one to refine only the regions of interest. This training case models a pseudo-2D situation.
Thin Gap Meshing and Refinement
SnappyHexMesh allows using different strategies to refine different surfaces and regions. However, discretizing thin gaps in the domain can result in a challenging topic. Especial critical are meshing procedures in which only triangulated surface are available. As already mentioned, OpenFOAM allows different techniques to refine thin gaps. One of them is described in this tutorial.
Cell Zone Generation within SnappyHexMesh
Particular regions in a mesh could require unique properties such as the modeling of porosities or source terms. Therefore, cellZones has to be used in OpenFOAM®. SnappyHexMesh can be one way to define such zones during the meshing stage directly. Based on the snappyHexMeshDict set-up, different quality levels can be achieved. Especially the influence of the »featureEdge« feature is demonstrated in the training case.
2D Rotational Axis Symmetric Meshing
2D and 2D rotational axis symmetric numerical meshes are used whenever it is possible. This method is related to the savings in computational effort and simplification at all. However, there are several ways to create 2D rotational axis symmetric geometries in OpenFOAM®. For more complex designs, it is worth to analyze the following training case which uses the 3D meshing tool »snappyHexMesh« to mesh the geometry in 3D first, and afterward derive the 2D rotational axis symmetric model by using other OpenFOAM® tools such as extrudeMesh and so on.
A multiphase simulation using the solver interFoam to investigate into falling droplets. The training case was invented 2017 with a former colleague Christian Gomez Rodrigues to proof an interesting statement. Based on Holzmann CFD's lack of knowledge in the field of droplets, Weber number and so on, the case is more related to be a fun investigation rather than a scientific investigation. An outcome of the fast set-up is the beautiful fluid dynamics and the corresponding velocity field.