[daenerys]

Hi everybody,

I'm trying to mesh quite a simple geometry of a blade in a wind tunnel (see picture).
I want the area around the profile to be meshed with polyhedral cells, and the area away from the profile to be meshed with trimmed cells.

Initially, I've meshed the entire area with trimmed cells, but although the mesh was quite good, the flow was reversed for some reason...
When I changed the mesh to polyhedral, I got excellent results with excellent convergence behaviour, but I'd still like to use trimmed cells at the inlet/outlet regions.

I've built the channel as one part and assigned the different surfaces to regions.
I assume seperating the inlet/outlet regions into different regions could resolve my problem, but I can't seem to find a way to do it.

Help would be much appreciated!

[TimCFD]

Hi daenerys,

first of all, it is not possible to mesh one region with different volume cell types in STAR-CCM+.

What do you mean with the "flow was reversed for some reason" when using the Trimmer? Did you get reversed flows at the outlet? Use the Extruder model to avoid that.

In order to mesh the inlet & outlet area with the trimmed cell mesher and the blade with polys you need three regions. -> So your assumption is correct. Use Boolean operations to create three parts (under geometry) and assign them to regions (imprint the parts in order to create proper interfaces) and that´s it. But please keep in mind that the interfaces are not conformal meshed and you should definitely avoid interfaces when they are not absolutely necessary (interpolations take place).

I would do the following:
- use the Polyhedral mesher
- make the inlet & outlet shorter
- use the Extruder to mesh the inlet & outlet area

I hope that helps.

[daenerys]

Hi Tim,

Thanks for the reply. Your suggestion about the boolean operation helped.
Yes, I got reversed flow at the outlet when I used the trimmed cell mesher.

I'll try your suggestion regarding the extruder model as well. Where can I find it though? It's not under physical models.

[TimCFD]

The Extruder is a mesher (a 2.5D mesher). It can be selected under Mesh Continua models (it is currently not available for parts based meshing (with an Automated Mesh Operations)).

[daenerys]

Awesome, thanks.

I'm using the Badge for 2D Meshing and the Automated Mesh operations in order to mesh this geometry though.
Is there a way to use the extruder model in order to mesh a 2D geometry?
I suppose I'd have to use the region based meshing?

Sorry for the obvious questions, I've watched all the tutorials but I'm still trying to figure out how to implement all the different options this software has to offer.

[TimCFD]

If you have just a 2D mesh it is not really necessary to use the Extruder in my opinion. What you already have is not that bad. I mean we are talking about saving some cells in order to reduce the computational time for big simulations (not the case for most 2D runs).

You need region based meshing to use the Extruder and after the volume mesh generation there is an option "Convert Mesh to 2D" (something like that, it´s described in the UserGuide). But as I said, you don´t need that in my opinion.

[daenerys]

Yes, I think you're right, I'm just trying different things in order to inspect different convergence behaviours.
So far, I got the best behaviour and the most accurate results with the polyhedral cells...

Thanks very much for your help!