Grid convergence study StarCCM+
 

Hi,


I am currently performing a grid convergency study using StarCCM+. The investigated airfoil is the NACA 63-415 with a chord length of approximately 0.6m. I decided to use an unstructured grid with prism layers. I am still a beginner and I would like to ask you some questions:


- I have to refine my grid in the direction normal to the wall (say y-direction). With how many prism layers do you suggest to start? In which way does the number of prism layers influence the accuracy of my results?



- I also have to refine the grid in chordwise direction (say x-direction) in order to capture the transition process. In this case, which parameters should I change?


- I don't fully understand the meaning of the base size. Can anyone explain it?


- How to I display the transition point?


I know these are a lot of different questions, but I would be really grateful if someone would answer them.

You can use a volume refinement and enable the anisotropic refinement option, that way you can specify different cell sizes in the x, y and z directions.
I suppose the question about the layers will be answered through the mesh sensitivity study. There are a few things to consider such as wall functions, y+, transition from the layers to the volume mesh...

Base size is what the words says, the (base) size of the cell. If you were to create a trimmer mesh for example with cells 100% of the base size, you would have all cells with the same size. With trimmer mesh each mesh refinement splits 1 cell into 4 cells. So you do the math.

What transition point are you talking about? Are you looking into laminar-turbulent transition?

Yes. I mean laminar-turbulent transition. I would like to display the exact position where the transition (laminar to turbulent) takes place.



I still do not understad the meaning of the base size. If the airfoil chord is 0.6m and I choose a base size of 0.006m, does it mean that the mesh will have 100 cells in chordwise direction?

I think the base size is only a reference value for your mesh generating. You should focus on the size of aim size and minor size.