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UDS and Periodic BC

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Old   July 19, 2002, 02:12
Default UDS and Periodic BC
  #1
iker
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Hello.. everybody....

I have a diffusio convection problem, and I'm trying to solve it with UDS. In fact, I'd like to set PEriodic Boundary conditions for the Scalar transport..

I wonder if someone has already tried it before,,and any suggestions to manage it are welcome.

thans from Switzerland...

iker

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Old   July 23, 2002, 08:58
Default Re: UDS and Periodic BC
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iker
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hello.. hello..I've changed the mail adresse..

once again .. Does anybody try to set Periodic BC for a User DEfined Scalar variable... in fact I'm working with a Diffusion/Convection stationary problem with a corrugated geometry...

thanks.. I need someone's suggestions..

iker

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Old   July 23, 2002, 19:58
Default Re: UDS and Periodic BC
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Matt
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Are you asking how to set a periodic boundary condition? Link the faces/edges in Gambit and then select both faces/edges in the boundary conditions panel and select "periodic."

Is this what you are looking for?

Matt
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Old   July 24, 2002, 02:34
Default Re: UDS and Periodic BC
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iker
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Bonjour, Hi Matt..

thanks a lot for the response...

My questions is not concerning how to do the mesh. I've already done it.. it's more concerning a solver problem (I'm working with fluent 5.6)

In fact, my geometry is a corrugated channel(like a period of a cosinus signal). This channel lies inside a straight tube. So I have a Navier Stokes with transport diffusion problem. I'm working with UDS for solving the tranport/Diffusion.

As boundary conditions I'd like to set Periodic COnditions trough the streamlines (like a cosinus signal with periodic geoemtry).

I run the case (laminar and stationary case) but afer a hundred of iterations the residual error starts oscilating... without geting the convergence...

So I do not know if I have to run a Turbulent case, or if I made a mistake somewhere, or if it's possible to set Periodic Boundary conditions working with UDS...

thanks once again Matt,

from lausanne..

iker
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Old   July 25, 2002, 12:28
Default Re: UDS and Periodic BC
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Matt
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iker, The oscillating residuals is not uncommon. There are a number of issues surrounding why they do that. I went to the FLUENT Users Group Meeting and they informed me that there are often problems in the continuity equation that causes the oscillations. This problem happens if you have a large gradient in a value. (ie, if you have an inlet condition on your pipe and the you set a no slip condition on a wall.) My suggestion is to monitor other things in your model. I often monitor the mass-weighted average of the outflow velocity, or the average temperature on the outflow. These should level off even though your residuals don't.

Matt
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Old   July 31, 2002, 06:56
Default Re: UDS and Periodic BC
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iker
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Hello Matt,

I'm not sure I've understood what you proposed me..when you talk about displaying or monitoring other variables you're proposing to monitor them during solving processus???

Anyway, even if I achieve to display them, continuity residual curve will continue to oscillate??

could you give some more details concerning your proposition please?? t

thanks once again..

iker . .from geneva-lausanne
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Old   August 1, 2002, 00:11
Default Re: UDS and Periodic BC
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Matt
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Yes, the continuity variable will oscillate even though you are monitoring other variables. You see, residuals are only one way to monitor convergence. If you go to Solve --> Monitors --> Surface/stastistic/force/etc, you can define other things to monitor as a function of iteration number. (ie-wall shear stress or a mass-weighted average exit velocity). Usually when you define one of these monitors, you will see that they will converge to a solution. If this is converged, the rest of the model is likely converged even though your residuals oscillate. I know what you are experiencing. It has happened to me on a few occasions. However, I felt that my solution was correct by simply monitoring other parameters.

Matt-from Provo, UT--USA BYU Graduate Student
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