Learning Forum

[Alberto]

Hi community,

I've made a 3D transient simulation with the overset-mesh technique (with a background and component mesh). simulation results are fine, but i wuold like to look at the II invariant of the flow field, i mean to plot the Q-criterion inside a vortex region. I did it on CFD post but it looks weird, maybe the problem can be that i've saved the results in .cas, .dat and cdat format for the post - processing. Which format should i use to export correctly overset mesh results ? When i load them into CFD a warning message appears: "Note that: Fluent Overset meshes are not supported in CFD-Post. Results may be incorrect/invalid."

Furthermore, is there the possibility to do such type of plot ( Q-criterion in a vortex region) in Fluent instead of CFD- Post? I can't found the method to create such vortex region which is straightforward in CFD post.

 

Many thanks

[Rob]

CFD Post can't import overset results, hence the warning message. 

Q Criterion is available in Fluent, https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v242/en/flu_ug/flu_ug_fvdefs.html  (Open Help in Fluent & paste the link into the browser that opens). 

[Alberto]

Unfortunatly the link you provide did not open anything about Q-criterion, I've searched also in the fluent guide but it just says that the Q-criterion is available under velocity settings but i cant find any explanation on how to produce such plot.

 

[Rob]

Odd, it's the list of all the reporting variables in Fluent. Have you looked at the surface creation options in Fluent? 

[Alberto]

Yes but there's no options for creating a vortex core region, as in CFD post. I'm able to visualize the Q-criterion vortex region in CFD post, but its not smooth, how can i made the vortex smooth ? maybe if i'll plot on fluent it will be fine ?  Many thanks

[Rob]

We'd typically create an iso-surface of "something" and then plot another variable on that. 

[Rob]

And the maths behind the CFD Post approach is covered here,  https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v242/en/cfd_post/vort-core_details_v.html?q=vortex%20core  (open Help in Fluent then copy the link into the browser) if you want to code it into Fluent. 

[Alberto]

Many thanks, suppose I want to compute the Q-criterion by myself, which is the optimal format to save data ? Furthremore, i've looked at the iso surfaces in fluent but they are not what i would like to plot, i want to visualize the three dimensionl vorticity region, in CFD post i've tried with success but the resolution oft he vortices is non-smooth

[Rob]

How did you get the results into CFD Post? It's not designed to take overset meshes. 

In more general terms for other post processing tools I'd check what that could read and work from there. 

[Alberto]

with the extensions: .cas, .dat, .cdat.  

[Rob]

OK, I thought we'd already established that CFD Post didn't like overset results. 

 

[Alberto]

yes, when it open the files it says that results may be corrupted, but some features work

[Rob]

OK, so whatever you've got working is about as good as you're going to get. I suspect .cas and .dat will be safest as I'm not sure what .cdat will make of the overset results. cdat is a cut down format for CFD Post.