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-   -   C_VOF(c,pt) value increases every time step (http://www.cfd-online.com/Forums/fluent-udf/114664-c_vof-c-pt-value-increases-every-time-step.html)

IndrajitW March 15, 2013 05:45

C_VOF(c,pt) value increases every time step
 
Hi everyone,
I am simulating a two phase flow case in which a waterfront advances and I am using an UDF to track the interface. While I detect the advancing front and display the x-value of the centroid and also the VOF value in the cell by:
C_CENTROID(xc,c,t) and C_VOF(c,pt) resply,where ,pt= THREAD_SUB_THREAD(t,1), is the phase thread and t is the mixture thread. I have found that though the centroid does not change in two time steps the VOF value in the cell increases.
Does the VOF value get added instead of being calculated afresh every time step???
Please help.
Regards,
Indrajit

vasava March 18, 2013 03:41

Shouldn't 'pt' in C_VOF(c,pt) have an index e.g. pt(1) for the phase in question?

pt[i], an element in the array, is a pointer to the corresponding phase-level thread for the ith phase, where i is the phase_domain_index. Source: UDF Manual.

IndrajitW March 18, 2013 05:27

C_VOF increases
 
Quote:

Originally Posted by vasava (Post 414608)
Shouldn't 'pt' in C_VOF(c,pt) have an index e.g. pt(1) for the phase in question?

pt[i], an element in the array, is a pointer to the corresponding phase-level thread for the ith phase, where i is the phase_domain_index. Source: UDF Manual.

Hi,
Vasava,
Thank you for your attention. However my THREAD_SUB_THREAD(t,1) specifies the required index and hence pt is not array of threads in this case but just thread pointer to the phase thread.So I guess that should not be a problem. Any thing else that can affect the VOF value to increase???
Regards,
Indrajit

vasava March 18, 2013 06:16

I can't think of anything right now. Does this happen in between the simulation or from the beginning.

IndrajitW March 18, 2013 09:08

Quote:

Originally Posted by vasava (Post 414635)
I can't think of anything right now. Does this happen in between the simulation or from the beginning.

Hi again,
When I start the simulation it shows some value and then every iteration the value keeps on increasing!!! I have not checked how long the value keeps on increasing but increase in the value at the same place with the interface not moving seems odd!!

vasava March 19, 2013 03:33

Did you use 'patch' after initialization?

If not then I suspect that this behavior is the effect of the initial condition or the initial state of the flow. You can run your simulation for bit longer and observe C_VOF. If it does not stabilizes to a reasonable range then there may be something wrong with the setup as well.

IndrajitW March 19, 2013 04:40

Quote:

Originally Posted by vasava (Post 414882)
Did you use 'patch' after initialization?

If not then I suspect that this behavior is the effect of the initial condition or the initial state of the flow. You can run your simulation for bit longer and observe C_VOF. If it does not stabilizes to a reasonable range then there may be something wrong with the setup as well.

Hi,
Yes I had used patch after initialization. Perhaps this behavior is an effect of the initial flow. I will see if I can observe stable values along some later time steps.
Regards,
Indrajit


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