The Prism Layer Mesher (PLM) and the Advancing Layer Mesher (ALM) are both used to create orthogonal prismatic cells in the near wall region so as to resolve the high gradients close to the wall. The purpose of this article is to highlight the small changes in the algorithms employed by the two meshers so as to choose the right mesher for your application. The two meshers are within the family of volume meshing tools of Simcenter STAR-CCM+.
A quick overview of the meshing philosophy employed in Simcenter STAR-CCM+, upon importing of a clean, water-tight volume. One can create a new mesh operation with Surface remesher and either Trimmer or Tetrahedral or Polyhedral mesher.
- Generate Surface mesh based on the specified user settings within the mesh operation
- Generate either irregular Hexahedral/Tetrahedral/Polyhedral elements based on the surface triangulation provided by the previous step
Now, upon selecting the Prism Layer Mesher the algorithm changes to:
- Generate Surface mesh based on the specified user settings within the mesh operation
- Generate a Prismatic sub-surface based on Total thickness specified within the mesh operation for all the boundaries/part-surfaces which need a Prism layer
- Generate either irregular Hexahedral/Tetrahedral/Polyhedral elements for the void from the sub-surface onwards
- Create the individual prismatic layers based on the number of layers prescribed in the mesh operation, starts from the surface upto to the previously created sub-surface
- Assemble the complete volume mesh
Finally, if the Advancing Layer Mesher is selected instead, the algorithm changes to:
- Generate Surface mesh based on the specified user settings within the mesh operation
- Generate a single prismatic layer based on the settings within the mesh operation
- Build the next prismatic layer, and so on until the maximum number of layers provided in the mesh operation is reached
- Generate either irregular Tetrahedral/Polyhedral elements for the remaining void between the last prismatic layer and enclosing surface
- Assemble the complete volume mesh
As you can see in the above algorithms the ALM can be used to create a rather thick, smooth and higher number of layers due to the intrisic design of the mesher, one application area could be External Aerodynamics where you need a rather thick prismatic distribution to capture the flow irregularities. An important limitation of the ALM is that it only works with the Tetrahedral family of meshers i.e. Polyhedral or Tetrahedral Elements, cannot be used with Trimmer presetly. On the other hand the PLM has no such limitations and is a more robust mesher. The sub-surface is generated firstly and then the number of layers are added, so if the sub-surface is thin the number of layers could be reduced so as to improve the overall quality of the resulting mesh. The PLM is suitable for Internal and External flow applications and specifically for complex and convoluted geometries, where the spacing is rather tight.