[alw7]

Good morning!

How do you determine your base size, target surface size, and maximum cell size?

Thank you!

[me3840]

The base size should almost always be the size of the largest surface edge length you want in your mesh.

Leave the target surface size in default values at 100%, and make surface controls for anything you want finer.

Determining if your mesh is fine enough is subject to experience and mesh refinement studies.

[LuckyTran]

It's helpful to understand the relationship between base cell size, target cell size, and maximum cell size in the Star-CCM interface because of how prevalent relative cell sizing should be.

The delta/10 rule is a good and almost universal rule-of-thumb. That is, any feature you want resolved should have 10 cells across it's dimension. You should go into meshing with some delta/# in mind. If you don't, you should experiment to get this experience.

[AndreP]

My "rule of thumb" to START meshing (before refinements that I find necessary) are:

Body/Flat plates no bigger than 100% of base size for Target.

Round surfaces I normally assign the minimum cell size of Half the radius of that surface!

As I said, this is a starting point. After this I analyse the mesh (mesh indicators and I look at the mesh to search for good resolution), and refine more areas that I need!

[LuckyTran]

The base cell size almost be set to just about any number because it's just a reference value. If you use absolute values in target surface size and minimum cell sizes then the base size is almost irrelevant because it's never needed. If you use relative sizes (which is the default) then the absolute sizes are calculated automatically using the % you give and the base size.

There is one exception, the minimum prism layer threshold is a % of the base size and there is a smallest possible value that Star will let you enter this percentage. In my opinion this is a bug in Star.

Originally Posted by AndreP

Round surfaces I normally assign the minimum cell size of Half the radius of that surface!

Note that there is a meshing option in Star-CCM labeled # pts / circle which helps to enforce this condition. Star always chooses the tighter constraint. It takes the smaller of the target cell size and the calculated cell size using the # pts / circle. But it will not generate cells smaller than the minimum cell size.