Learning Forum

[zoelle.wong]

Hello!

clarificatoin question: what is the difference between the volume-integral UDF and the heat transfer rate flux? I want to model an arc inside a domain. After separating two zones, I prescribe a UDS energy source term inside the arc. I know the arc should have X amount of energy in Watts. I normally calculate the heat transfer rate in the "arc" region to check the amount of energy.

My understanding is that the heat transfer rate is heat transfer between a surface to the fluid, but would this definition be the same if my "surface" is for a fluid region inside my mesh? I've attached examples of the flux reports that I'm questioning below. Thank you!

 

 

 

[Rob]

Check the definition of "volume average" in the User's Guide - I suspect you want sum. The other potential issue is that interior faces (surface rather than the interior that's every facet in a volume) don't have a normal assigned so you may find neighbouring cells have + or - values randomly. You may need align the facets to use the reports. 

[zoelle.wong]

I tried mesh/modify-zones/orient-face-zone to orient the interior facets and I got an error in the screenshot below. Is there another way to orient the interior faces?

The sum report type gave me a matching value for the total-heat-transfer-rate in flux reports - thank you!

 

 

[Rob]

Odd, zone 11 is the interior surface and not the cell zone? 

[zoelle.wong]

zone 11 is a cell zone- I separate the domain into two zones. Does this command only work for internal surfaces?

 

[Rob]

It's for the interior that bounds the cell zone; ie the face separating neighbouring fluid zones.  Trying it on the interior that is the cell zone will cause problems as the zone ID is the same on both sides of the facet. 

[zoelle.wong]

ohh ok - do you know of a command that would work if the zone has facets on both sides? Otherwise it seems the sum-volume integral is the best way to check 

[Rob]

That command works on the surface interiors, don't use it on the "volume" interiors. The distinction is important as the former typically have cells on both sides too. In your case as it's a volume you should use volume reports. 

For various reasons Fluent must store the volume-interior facets in a surface label; it's generally a very bad idea to interact with that label. 

[zoelle.wong]

ohh ok- thank you!