# Mesh

The Mesh

The principle is quite simple : the two regions defined before are meshed separately : the software will automatically deactivate the cell of the background mesh which are not useful. Indeed, the Navier Stokes equations won't be solved in the background cells which are close to the blades geometry (in the area close to the blade geometry, the equations will only be solved in the moving mesh).

First, create two mesh continuum : do twice the procedure right click on Continua $\rightarrow$ New $\rightarrow$ Mesh Continuum. Rename one as "moving_mesh" and the other as "background mesh".

On the region domain : region $\rightarrow$ right click on domain $\rightarrow$ Edit $\rightarrow$ Mesh continuum $\rightarrow$ "background mesh". Same procedure for the "moving_region" domain $\rightarrow$ Mesh continuum $\rightarrow$ "moving_mesh".

For both meshes, it is now necessary to select the models to use : righ click on models $\rightarrow$ Polyhedral Mesher and Surface Remesher for the background mesh and Polyhedral Mesher, Surface Remesher, Prism Layer mesher and Surface wrapper for the moving_mesh.

The values used here for the moving mesh are :

For the background mesh :

It is important that the cell close to the geometry in the background mesh have the same order of magnitude in term of size. To achieve that, let us create a Volume shape : Tools $\rightarrow$ right click on Volume shapes $\rightarrow$ New Shape $\rightarrow$ Block. This block must be at lease the size of the moving region.

Now it is possible to add a volumetric control :

right click on Volumetric Controls $\rightarrow$ New $\rightarrow$ Select the shape just created and use Polyhedral Mesher and Surface Remesher with a relative size of 2 (which gives 1m, the base size of the moving mesh).

From this point, one can create the mesh by clicking successively on .

Make the Mesh Moving

To make the mesh moving, Tools $\rightarrow$ right click on Motions $\rightarrow$ New $\rightarrow$ Rotation. Click on rotation $\rightarrow$

Now that the rotation is created, it is necessary to let the software now that we want to assign this Motion the moving_region :

here,

Right click $\rightarrow$ Motion $\rightarrow$ Rotation

Visualize the mesh

To get a 3D view of the mesh (like the first image of this page), a "Threshold" derived part is used. It makes it possible for the user to display cell which meet a specific criteria.

Right click on Derived part $\rightarrow$ New part $\rightarrow$ Threshold $\rightarrow$

Right click on Scene $\rightarrow$ New Scene $\rightarrow$ Mesh in the onglet Plot/scene ():

Finally :

Finally, it is possible to set up the simulation.