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Old   April 2, 2010, 05:24
Default convergence issues
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Francis
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hi

im actually working on a simple flow case ( im a beginner), a cylender obstacle. im trying to hav von karman streets but first i would like to converge my calculation in steady. i had difficulties to hav it converged...i tried to change under relaxation factors, AMG post sweeps...nothing changed

please help me
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Old   April 2, 2010, 06:25
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zhwan
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Try set Reynolds Number lower. Generally, if the Re < 47, you will get a converged solution.
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Old   April 2, 2010, 07:32
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Hamid Zoka
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Dear Francis;
is the flow turbulent or laminar?
please note that if you are to solve a flow field without using any turbulent model, you should be sure that your flow is totally laminar.
if you use ordinary form of navier-stokes equations for a turbulent flow your solution will not converge.
firstly check your code with laminar regime.
then, if you like to switch to turbulent flow, you should know how to apply turbulent models to navier-stokes equations.

regards
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Old   April 2, 2010, 08:21
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Re is 70 000. n i use kw sst turbulence model
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Old   April 2, 2010, 08:23
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thx for answering again
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Old   April 2, 2010, 08:53
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hi,
As i know,many people want to get converged solution for analyzing the flow stability.
The flow is unsteady at a high Re. For a 2D cylinder, the transition Re is about 47, Re~180 for 3D.

u can use a unsteady solver such as explicit time -marching scheme for the problem.
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Old   April 2, 2010, 10:07
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Francis
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the tke is not converging.... zhwan im doing a specific calculation i hav to converge befor moving to unsteady

please help me!
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Old   April 4, 2010, 09:21
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hugocis, which method you currently use, Newton's iteration(GMRES) ? you can try to change the solver such as RPM ( Recursive Projection Method) .This method can be applied to both steady-state or unsteady caculations.

The following is a thesis about RPM
------------
[PhD Thesis]Aspects of the RPM applied to flow solver. Author: Jokim Moller.
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Old   April 6, 2010, 03:35
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ok but i dont even know wat u talkin about im usin gauss seidel , AMG solver if that help....
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Old   April 6, 2010, 03:43
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now i have turbulen viscosity limited in 570 cells in ...
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