Converge and diverge

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 February 23, 2002, 07:36 Converge and diverge #1 Jack Guest   Posts: n/a Hello, everyone, I am using low-reynolds k-e model to simulate the flows in ducts with periodic condition. The reynolds stress is model by EASM. However, I have difficult to make the program converge. The iterations always oscilate within a certain range. However, the results with the lowest converge critia are very close to the correct solution. Could anybady give me any idea how to improve it? Thank you very much Jack

 February 23, 2002, 10:14 Re: Converge and diverge #2 wang Guest   Posts: n/a As I understand, you use time-dependent solution. What kind of time discretization do you use? or Have you try to ever decrease the time step?

 February 24, 2002, 08:02 Re: Converge and diverge #3 Jack Guest   Posts: n/a it is a steady state calculation.

 February 24, 2002, 09:21 Re: Converge and diverge #4 wang Guest   Posts: n/a Hallo Jack, my first question is, how can you simulate the periodic condition with steady solution? If your computation is a steady one, and it doesn't converge, it may mean that 1). The solution is an unsteady one, hence you can not get steady solution. There is numerical diffusion that prevents the solution be not diverged. Try a time-dependent solution. 2). Grid quality. It may be that you have some coarse resoltuion at locations where there is strong gradient. Try to check your grid. hope this help.

 February 24, 2002, 23:43 Re: Converge and diverge #5 john Guest   Posts: n/a I second to Wang's suggestion on checking your grid. Personally, I had used low Re model in StarCD, and sometimes it never get to the standard convergence criteria. Because I used very fine mesh, and maybe also bad mesh quality, I could pick up turbulence without using turbulence model, to some extent. So, never had a steady state solution.

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