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Periodical boundary condition conflicts with inlet boundary condition
Posted Jul 31, 2015, 3:48 a.m. EDT Computational Fluid Dynamics (CFD), Modeling Tools & Definitions, Parameters, Variables, & Functions Version 5.0 1 Reply
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I am doing a simulation of a tube. To reduce the calculation scale, I would like to simulate only a little portion of this tube by using periodical boundary condition. By this boundary condition, I want to link the inlet and the outlet of this small pipe.
But the problem is that I can't apply the inlet boundary condition . That's because the inlet boundary condition will be overridden by periodical boundary condition.
In order to solve the problem, I set the initial velocity as the same as the designed inlet velocity. However, since the wall is not a slip wall, the flow will come to a steady state when all the energy of flow is dissipated and the velocity becomes almost zero.
Is there anyone who can help me to solve this puzzle? Thank you!!!
But the problem is that I can't apply the inlet boundary condition . That's because the inlet boundary condition will be overridden by periodical boundary condition.
In order to solve the problem, I set the initial velocity as the same as the designed inlet velocity. However, since the wall is not a slip wall, the flow will come to a steady state when all the energy of flow is dissipated and the velocity becomes almost zero.
Is there anyone who can help me to solve this puzzle? Thank you!!!
1 Reply Last Post Aug 4, 2015, 3:16 a.m. EDT
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Posted:
9 years ago
Hi
Normally in fluid flow you define a velocity and fix a gauge pressure somewhere and you are done, if you have a periodic condition you impose an input and output velocity, remains only the pressure drop as free parameter, so you must define this pressure drop to drive any motion of your fluid. Remains that you need to fix the pressure somewhere via a "point pressure".
These conditions are defined in the fluid SPF periodic boundary condition (do not forget to define the "destination" or outflow region) and to fix a pressure point
Now the convergence might be somewhat tedious, if you leave the full cross section flow free there are many free DoF while one know (at least in laminar flow) that the flow shape is rather parabolic, but you will not get a constant pressure in and out. One can also play a little with the pressure constraints at the inlet/outlets.
I notice that convergence is tricky, but it should work better if one ramp up slowly the flow with a parametric sweep (not done hereafter) my "toymodel" is a v5.1.0.180 version
--
Good luck
Ivar
Normally in fluid flow you define a velocity and fix a gauge pressure somewhere and you are done, if you have a periodic condition you impose an input and output velocity, remains only the pressure drop as free parameter, so you must define this pressure drop to drive any motion of your fluid. Remains that you need to fix the pressure somewhere via a "point pressure".
These conditions are defined in the fluid SPF periodic boundary condition (do not forget to define the "destination" or outflow region) and to fix a pressure point
Now the convergence might be somewhat tedious, if you leave the full cross section flow free there are many free DoF while one know (at least in laminar flow) that the flow shape is rather parabolic, but you will not get a constant pressure in and out. One can also play a little with the pressure constraints at the inlet/outlets.
I notice that convergence is tricky, but it should work better if one ramp up slowly the flow with a parametric sweep (not done hereafter) my "toymodel" is a v5.1.0.180 version
--
Good luck
Ivar
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