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September 6, 2010, 06:47 |
local time step
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#1 |
New Member
sungho yoon
Join Date: Mar 2009
Posts: 20
Rep Power: 17 |
Hello.
I'm doing a calculation which simulates a steam turbine diffuser. I generally use a local time step which I gradually increase from 1 to 50. This is generally okay for most of my cases. However, for some outlet boundary conditions, the calculation does not converge and the flow separates significantly. When I have these cases, I can often (not always!) make the solution converged by increasing the local time step to a very large number (say 200) I wonder what this means. Does it mean that my actual time step (delta t) is increased significantly and misses small time scale fluctuations? Kind Regards, |
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September 6, 2010, 07:37 |
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#2 | |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,729
Rep Power: 143 |
You should not use local time stepping for the final run to convergence. Always use physical timesteps on the final run to convergence.
Quote:
Your experience agrees with the comments on the FAQ about convergence in steady state simulations: http://www.cfd-online.com/Wiki/Ansys...gence_criteria |
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