Mesh is the STEP required in order to define the mesh.
In this section the user is asked to define the mesh algorithm and the basic mesh feature.
Meshing algorithm: drop down list from which the user has to select the meshing algorithm (see pictures below).
Mesh smoothing: uniformity level of the volume mesh assigned as a percentage.
In this section it is possible to define mesh local refinement for each of the considered surfaces.
Boundary treatment: selection of the boundary using an accordion menu.
Mesh uniformity: percentage that defines how rapidly the basic elements dimension grows.
Maximum mesh size: it defines the local mesh refinement (i.e. the element size) on the selected surface.
In order to choose correctly the Maximum mesh size it is important to run a convergence analysis.
In this section it is possible to activate the boundary treatment (i.e. boundary layer) for wall resolution in CFD simulations. As showed in the following image, the boundary layer is a zone where the surface mesh is extruded in direction normal to the external surface. The user can here customize this type of extrusion by defining the number of cells to be extruded and the dimensions of the extrusion zone. This operation is fundamental when dealing with a CFD simulation since the quality of the results depends on the wall distance of the first fluid cell.
First wall cell height and y+ are mutually influenced. Remember to decrease the cell height if y+ is above 300 for k-epsilon or 1 for other turbulence models. Several y+ estimator are available online to give guidelines about the wall cell dimension.
After having completed this setup, the user can finalize the step by clicking on the Submit button. This will start the Mesh step application that will show up in the Case in progress section of the main Simulation page.
Once the mesh step is completed, using the graphic interface it is possible to view the obtained grid. Mesh quality is reported with a certain number of variables which highlights problematic cells. The most common variables are:
CONSELF automatically impose some fixed thresholds for all these problems. When this threshold is passed the cell is highlighted as low quality. The highlight mechanism is rather simple: all these variables are assigned a 0 value where no problem is present, 1 where the problem is present. In order to view the mesh zone where quality test fails it is necessary to filter and extract the problematic zone as described in this tutorial.
More information about mesh quality are available in our blog:
CONSELF is constantly producing more and more tutorials and guidelines to users so they can get benefits out of CFD/FEM simulations. In particular, referring to meshing, you can find a certain number of posts by visiting this page.