Volume average of a scalar?
Can anybody help me with this please? I have a flow field with one volume and I want to calculate the volume averaged scalar concentration in a sub-volume.
It is easy to do for the whole volume (report->volume integrals) but how do you create a sub-volume not part of the mesh file? You can only create points, lines and surfaces in the Fluent GUI, any tricks for creating a volume?
I have released the scalar from a sub-volume using a UDF but I'm having difficulty calculating the scalar concentration in other sub-volumes. I do have other models with the volumes decomposed already but its not very efficient if you need to know a volume average somewhere else.
Any help is much appreciated.
There is not a simple solution to your problem.
However I do this:
- Define a User defined memory (UDM, under fluent-> define->user-defined-> Memory).
- Define as a user Field function the variable you want to average
- Patch UDM to zero for the whom volume
- Define your sub-volume in the Fluent-> Adapt-> Iso-Value or Region or Volume
- Patch the User Field function to the UDM for Registers to Patch -> (Name of volume)
Now your UDM stores the variable inside the defined volume and Zeros in the other places.
Now a Sum in the whole volume will give you the SUM in the sub-volume.
With a few calculations you can get average values.
I hope this helped.
The other way is to do it via UDF
If your subvolume is a hex, sphere, or cylinder, you can use the adaption tool to create registers to mark the cells of your subvolume.
This is done under the Adapt->Region menu. Combine registers of spheres and cylinders to get complex shapes --- if necessary.
Once you define your registers, do NOT adapt them. Instead, go to the Grid->Separate->Cells menu.
Use the adaption register to separate the volume using the adaption register. This will split off the cells and create the sub-volume.
You can simply go to your Report->Volume integrals menu now and integrate your quantity on the newly created sub volume.
You can merge the volumes back together if necessary.
Bill Wangard, Ph.D.
I didn't know that!
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