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Convergence in Flow between corotating disks

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Old   December 5, 2003, 12:06
Default Convergence in Flow between corotating disks
  #1
Felipe
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Hi everybody,

My model do not convergence, I am searching the cause of it but I have not found,

My model is a Sink Flow between corotating disks. I set the following: 2D Axisymmetric swirl, steady, Laminar,incompressible. Boundary conditions, inlet_velocity, outlet_pressure, walls with rotational speed.

the three components of velocity convergence but the Continuity do not convergence, the flux report presents a difference value of 0,0344 % but this value is not so representative if the solution do not convergence. Ive tried it, decreasing the under_relaxation factors, Ive checked the mesh and check the boundary conditions. Also I reduce the inlet velocity (to assure laminar) and convergence is not reached.

Please, help me. Id appreciatte your suggestions

Felipe Rey
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Old   December 5, 2003, 13:06
Default Re: Convergence in Flow between corotating disks
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ap
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What kind of discretization scheme are you using?

Try to obtain a converged solution with first order, then switch to second or higher order schemes.

Hi

ap
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Old   December 5, 2003, 14:42
Default Re: Convergence in Flow between corotating disks
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Felipe
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Hi ap

thanks for your help

pressure : PRESTO! P-V coupling: Simple Momentum, swirl velocity = Second order Upwind

Ive made changes on discretization to first order schemes and the continuity do not convergence.

Felipe
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Old   December 6, 2003, 08:59
Default Re: Convergence in Flow between corotating disks
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ap
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I don't know if it will work in your case, but sometimes increasing the under-relaxation factor of Pressure to 0.5-0.6 helps in continuty convergence.

Try something like:

Pressure -> 0.5 - 0.6

Momentunm -> 0.4

Hi

ap
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Old   December 8, 2003, 09:18
Default Re: Convergence in Flow between corotating disks
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Felipe
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Thank you for your suggestion, but in my case increasing the URF for pressure didnt help, continuity continue without convergence. Besides the residuals for continuity stabilize, and get a value of 0.15 and the criterion I am trying to reach is 0.001.

At first I used: pressure 0.3 density 1 body forces 1 momentum 0.7 swirl velocity 0.9

and I tried pressure 0.6 and 0.9 density 1 body forces 1 momentum 0.4 swirl velocity 0.9

My geometry is small in x coordinate (trying to get laminar flow) (0,508mm X 101.6 mm). Re=30 (Reynolds for pipes using Hydraulic diameter.

I hope you or someonelse have more suggestions. Thanks

Felipe
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Old   January 5, 2004, 07:32
Default Re: Convergence in Flow between corotating disks
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sijal ahmed
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it is not necessary that u get 0.001 for convergence. some times although solution has been reached but still the value do not go beyond some limit as in ur case.

second way may be using double precision

also refer to fluent manual for further help
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Old   January 6, 2004, 07:18
Default Re: Convergence in Flow between corotating disks
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Felipe
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Thank you for your suggestions sijal ahmed

My model is already convergenced, the residuals definition is different as in FIDAP and just changing the initial conditions to others not so closed to final solution, the convergence under 0.001 appears. So, it is true that is not necesary to reach this value of convergence since the values of the solution dont change anymore.

thanks again Felipe Rey
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Old   January 27, 2004, 11:20
Default Re: Convergence in Flow between corotating disks
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ace
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its better for you to read Fluent manual for convergence..... Hope it solves your problem
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