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Laminar flow over airfoils

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Old   June 16, 2007, 14:55
Default Laminar flow over airfoils
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Murthy
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Hi people!!! can anyone please tell me if non-convergence of solution can be taken as an indication of change in flow regime?? like from laminar to turbulent ; steady to unsteady etc..
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Old   June 16, 2007, 14:59
Default Re: Laminar flow over airfoils *NM*
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Murthy
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Old   June 16, 2007, 17:32
Default Re: Laminar flow over airfoils
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Phil
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Non-convergence can be caused by a huge number of things. Even experts need to monitor convergence and sometimes go back and improve the grid.

However if you try to solve an unsteady problem with the steady solver you will experience this problem.

You could try using the unsteady solver to see if the solution changes.

I'm unsure about the turbulent transition although solving in laminar is simply computing all the individual turbulent scales directly ie not modeling them (DNS), but needs huge grids up to 8million cells to properly resolve the turbulent regions. I know this is incredibly difficult to converge.

Using a turbulence model for laminar flow shouldn't hinder convergence but is a waste of time.

Also when something downstream affects something upstream later in the solution, it causes the code's guesses to unconverge for a while as they re-calculate the new solution.

YOU SHOULD LOOK UP WIKIPEDIA.COM, ANY CFD BOOK, OR THE FLUENT/CFX DOCUMENTATION.

hope this helps Phil.
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Old   June 19, 2007, 11:43
Default Re: Laminar flow over airfoils
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Murthy
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Thanks Phil... you said "Using a turbulence model for laminar flow shouldn't hinder convergence but is a waste of time." so do u suggest that turbulence models are capable of solving laminar problems? and do u think i should try with a refined grid, the same problem?
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