# Grid convergence study StarCCM+

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 June 21, 2021, 07:54 Grid convergence study StarCCM+ #1 New Member   Join Date: Jun 2021 Posts: 8 Rep Power: 2 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.

 June 22, 2021, 03:53 #2 Senior Member   Lefteris Join Date: Oct 2011 Location: UK Posts: 249 Rep Power: 13 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? __________________ Lefteris

 June 25, 2021, 11:42 #3 New Member   Join Date: Jun 2021 Posts: 8 Rep Power: 2 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? Last edited by mtheory; June 25, 2021 at 11:42. Reason: Grammar errore

July 13, 2021, 23:14
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Rinia
Join Date: Jan 2018
Posts: 38
Rep Power: 6
Quote:
 Originally Posted by mtheory 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.

 Tags airfoil 2d, base size, grid convergence study, prism layer, starccm