Using created surface to measure mass flow rate
 

Hello,

In Ansys CFX, I have a pipe system from which I have extracted the water volume. I have created surfaces in different sections of the water volume (using the surface from edges) so I can check the flow through the different pipes, but either I have an error telling me these surfaces cannot be imported in PRE, or either they do not appear if I set them as construction elements.

How can I use surfaces I created to calculate the mass flow rate through them.

Thanks!

I would do this in CFD-Post not in CFX-Pre.

Ok, but how can I import/see/work-with these surfaces I created? They don't appear anywhere.

You can easily analyze the water volume in CFD-Post by creating contours at different cross sections/planes. CFD-Post is built for these things. Hope it helps.

This I understand and know how to do, but I want to get quantitative values of the flow, not just nice plots. For example, the mass flow through certain pipes.

Unfortunately, due to the way the CAD model is, there is no cross-section surface I can directly select and ask Ansys to compute things from (hence why I created these surfaces).

But I don't know how to use these created surfaces to compute information. This information seems to be hard to find. Why?

Go under: =>Calculators tab click => function calculator
In cfx post ofcourse

make your expresion by clicking the boxes here you will be able to see your plane under location.
there is probably anithing you like to calculate

This baffled me too when I started to use CFX. In STAR-CCM+, you can just add surfaces in pre processing and create monitor points on those surfaces (massflow etc). In CFX, you can't do that. Don't ask me why. It's super annoying.
In CFX Post, you can add those surfaces but that is not really an option if you want to monitor/plot for example the massflow through a specific surface over time.

For a year or so now, you can add "user surfaces" for monitor purposes in PRE, but that feature hasn't really worked for me so far. Haven't tried with Ansys 18 yet though
further reading:
https://www.cfd-online.com/Forums/cf...nitor-cfx.html
https://www.cfd-online.com/Forums/cf...rfaceuser.html

Yea I know this, but the surface I created in the design modeler doesn't appear in cfx post.

Exactly! I still don't know how to do it.

One way I tried is to create a plane and impose a circular radius to its radius so that it only covers the pipe I want the measure on, but it is a real pain to do it for many different pipes!

there is a way,
you can split the domain into two pieces vith that plane, than you are able to make a interface and that can be your plane in cfx pre you can than make monitor point for this conection

true, but you then have to rely on Ansys "power" to not screw up the interface numerically.
Or is that trick "common practice" for CFX users?

It is probably not common, this is more of a workaround the problem

I don’t see any problems at the interface, the connection can easily be meshed node to node (1:1) and CFX won’t even know it is there.

Of course I don’t use this method but it should work.

So the problem is how to create many planes? Because as you already said you can do that with monitors.

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flowrate = massFlow()@surface_in_question

That is the expression I'd use. That should give you the flowrate.