CFD Online Discussion Forums - UDF to constrain one of the phase to stay in the domain

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Hi Rubblevg,

You said"The define_source UDF needs to be set for the phase that is to be removed and it needs to be applied to a small volume close to the wall that represents the mass sink/outlet" DO you main to create a zone near the outlet or the wall to applied the mass source UDF? or I need to set for the layer of cells next to the outlet? If this is the case can you please let me know how to create one?

Thanks for your support
Hussein

Hi Hussein,

Sorry for my late response!

From your first message I conclude you don't fully understand my explanation of the UDF. The mass sink is meant to work as a replacement for the outlet, because an ordinary outlet in Fluent cannot work on only one component. Therefore you will need to remove your current pressure outlet if you want to apply the mass sink. Of course, you may be able to modify the equations of the mass sink to work exactly as an ordinary pressure outlet would.

As an answer to your second message I will give the reply I already sent you privately. This way, anyone can use the information :)

You need to create a small volume close to the wall where the outlet is supposed to be. On this volume you can apply your mass sink, so that it effectively functions as an outlet. Of course you won't need your original outlet then anymore, so you can replace it with a wall.

You can make the small volume by creating an additional body when setting up your geometry. In Ansys DesignModeller, you can do this by using the extrude function with 'add frozen'. This way, you create an additional body. Give the main body and the small body close to the outlet both names with 'named selection' and merge them together by using 'form new part'. Then, Ansys will recognize both bodies as one part while being able to set different source terms per body.

Note that when creating these two bodies it is important to create an interface between them. There are several tutorials on the internet about creating interfaces with Ansys, so I won't explain it here.

I hope this helps!

Cheers,
Ruben

Quote:

Originally Posted by H.Almrayatee (Post 671357)

Thanks Rubblevg, for your reply.
The BC are velocity inlet and pressure outlet, I can't change to another outlet because outflow BC is incompatible with Eulerian, also can't use the degassing due to the gas surface above the liquid primary phase. so pressure outlet is the best to use. Unfortunately I'm still get mass decreasing, I notice drag law used is also effect the case, now I change to another law "Symmetric" now mass is stable for 2 second but after that is start to decrease.
Any other thoughts?

Now I am facing the same problem. The backflow fraction for gas only set to be 1.0, the simulation can be run. But this will decrease of water

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I`m having multiphase simulation of nanofluid passing through a horizontal pipe using Mixture-model. How to assign phase velocities in velocity inlet condition as I`m having mixture velocity data only. Is a UDF is required for phase velocity? Kindly help.