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qrie July 1, 2013 08:57

Solution changing with dt.

I have a code in cylindrical coordinates that uses central differences. My problem is this: when I change the time step size, keeping everything else the same(grid included), I get vastly differing solutions.

Been breaking my head over this - any ideas??

Thanks in advance!

cfdnewbie July 1, 2013 11:21

Are you talking about a steasy state problem or an unsteady one?

qrie July 2, 2013 01:01

Its a steady state problem.

cfdnewbie July 2, 2013 03:18

Are you using an implicit or explicit solver for this?

qrie July 2, 2013 04:25

Advection terms are explicitly calculated. Viscous terms in the radial direction alone are implicitly calculated.

FMDenaro July 2, 2013 05:09

I think that the discussion of your problem must be better focused:
- what variable you see that strongly change with dt?
- what about the cell Re number? are you sure to fulfill the stability constraint?
- have you experienced the same behavior for refined h steps?

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