Using Scale in ANSYS

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  • Last Post 03 February 2020
morganj32 posted this 21 January 2020

I am trying to conduct some analysis in Fluent on a geometry with a cube enclosure of sides 1.26km long. When I open this in ANSYS meshing the program crashes regardless of the computer I use (before any meshing is done) and scaling the geometry down solves the problem. I suspect it is a problem with ANSYS Meshing as colleagues have made similar sized meshes in ICEM before.

I need to conduct my analysis on the full scale model but would like to still use ANSYS Meshing. I notice in Fluent there is the scale function so my question is, can I scale the geometry down by 10%, mesh the smaller geometry then in Fluent scale things up by a factor of 10?

I tried running basic simulations on two different size models using this technique and got different solutions however I am not sure if that is for another reason because I am still relatively new to ANSYS.

Thanks in advance.

 

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rwoolhou posted this 21 January 2020

Scaling works fine in Fluent, we often scale by 1000 or 0.001 too given the confusion of mm and m during model builds. Workbench Meshing shouldn't fail for larger domains, double check it's seeing 1600m in metres and not 1600m in mm: the latter could mess with the numerical precision. 

Note, we tend to scale in Fluent rather than in CAD to avoid CAD tolerance issues. 

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morganj32 posted this 21 January 2020

Thanks for your reply. 

I just had another try opening the full scale geometry in design modeler and it is too slow to work with (takes around 10 mins just to open) so I will use scale if possible. 

Your last sentence has me slightly confused, I was talking about scaling in both CAD and Fluent - scale down in CAD, import to design modeler, mesh in ANSYS Meshing then scale back up in Fluent before setting up the simulations, is this what you thought I meant?

rwoolhou posted this 22 January 2020

That approach should be fine. I tend to avoid scaling in CAD as it's less accurate than in the solver simply due to the way CAD data is stored/created. 

Your other option is to do the meshing in Fluent Meshing using the watertight geometry workflow: generally easier than Workbench.  

morganj32 posted this 29 January 2020

Sorry for the late reply, i had to do other things but thank you for your help so far. 

The part of your reply I do not understand is how you do the scaling in the solver instead of CAD. I am scaling in both: CAD to scale down 10% then the solve (Fluent) after meshing to scale up 10%. How could I scale it down in the solver before meshing it?

rwoolhou posted this 31 January 2020

If you're in the solver there's a scale button. I tend to read anything (CAD scale) into Fluent Meshing and then sort the scale out afterwards. This means I can read in models in inches, feet, metres and occasionally km, mesh with a suitable cell size and then scale later. I always avoid any scaling in CAD if I can. 

 

morganj32 posted this 02 February 2020

Sorry I still do not understand, it sounds like you are talking about something different to what I am doing. 

To be clear, when you say solver do you mean Fluent? I cannot read the unscaled geometry into Meshing - that is what causes the problem for me. 

rwoolhou posted this 03 February 2020

OK. Can you read the unscaled geometry in Fluent Meshing?  

 

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