UDF Outputs dont match exactly for volumetric heat generation.

nvarma · December 31, 2015, 11:19

I checked and crosschecked and backcalculated and everything.

I have a volumetric heat generation rate set as a function of coordinates. If I manually calculate the numbers (which I have set in the udf) I get say 10kW exact. But when it comes to udf, the total volume integral is only 9500W.

The contour plot makes sense. Heat balance is exact. But the 500W difference?

Anybody?

`e` · January 2, 2016, 18:38

Are you calculating heat generation at the nodes or cell centres? What is the UDF you are using to calculate the volume integral?

nvarma · May 23, 2016, 09:55

Based on cell centres.

I have come to the conclusive assumption that this is the discretization error from the mesh?

`e` · May 23, 2016, 18:41

The mesh would need to be quite coarse to be missing 5 % of the heat generation (try mesh refinement). What is the UDF you are using, are you sure it's calculating across the full volume?

December 31, 2015, 11:19	UDF Outputs dont match exactly for volumetric heat generation.	#1
nvarma Senior Member nm Join Date: Mar 2013 Posts: 100 Rep Power: 13	I checked and crosschecked and backcalculated and everything. I have a volumetric heat generation rate set as a function of coordinates. If I manually calculate the numbers (which I have set in the udf) I get say 10kW exact. But when it comes to udf, the total volume integral is only 9500W. The contour plot makes sense. Heat balance is exact. But the 500W difference? Anybody?

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January 2, 2016, 18:38		#2
`e` Senior Member Join Date: Mar 2015 Posts: 892 Rep Power: 18	Are you calculating heat generation at the nodes or cell centres? What is the UDF you are using to calculate the volume integral?

May 23, 2016, 09:55		#3
nvarma Senior Member nm Join Date: Mar 2013 Posts: 100 Rep Power: 13	Based on cell centres. I have come to the conclusive assumption that this is the discretization error from the mesh?

May 23, 2016, 18:41		#4
`e` Senior Member Join Date: Mar 2015 Posts: 892 Rep Power: 18	The mesh would need to be quite coarse to be missing 5 % of the heat generation (try mesh refinement). What is the UDF you are using, are you sure it's calculating across the full volume?