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Old   July 19, 2004, 15:44
Default Second order convergance.
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Hello All,

I am trying to get a 3-D case to converge of a laminar flow around a vertical cylinder protruding from a ground plane. From other cases that I have seen the only way to get the horseshoe vortex to appear in the corner of the ground plane and the cylinder you need to have second order accuracy. When I run the case with first order accuracy the residuals become very small (10^-6) and the cl and cd converge to a constant value. If I then switch to second order accuracy the residuals will not get lower than 3*10^14 and the cl and cd oscillate and never converge. Is there something else that I need to do to get reliable second order results. I thought that if I let the first order solution to converge then switch to second order that it should help with convergance. Any help would be appreciated.

Thank you in advance...Rob
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Old   July 20, 2004, 02:59
Default Re: Second order convergance.
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Hi Rob,

It does not sound as if you are running a transient simulation? This would be important to capture vortices and other dynamic features. Make sure you choose a time-step small enough to resolve the transients in the flow as well.

good luck...
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Old   July 20, 2004, 10:49
Default Re: Second order convergance.
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That is right, I was running a steady state solution. I have yet to venture on to the unsteady time-dependant solutions. Will changing to the unsteady solution make the difference you think? Thank you for your response Mystic.
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