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- - **UDS and Periodic BC
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UDS and Periodic BC
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 |

Re: UDS and Periodic BC
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 |

Re: UDS and Periodic BC
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 |

Re: UDS and Periodic BC
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 |

Re: UDS and Periodic BC
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 |

Re: UDS and Periodic BC
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 |

Re: UDS and Periodic BC
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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