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May 2, 2012, 05:12 |
CFD-number-segregated solver
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#1 |
Senior Member
Join Date: Feb 2011
Posts: 140
Rep Power: 15 |
Dear all,
I want to simulate a transient case for an incompressible fluid (mixture: contrast agent bolus in blood) using a segregated solver and have some general questions concerning the CFL-number: I read in some threads that the CFL-number ist important for stability reasons at coupled solvers. But do I have to take care of the CFL-number at segregated solvers as well? And is it just a stability reason or may I also get wrong results if I choose a time step which is too large for my grid or a grid size which is too small (at using a segregated solver as well)? I just thought I might get wrong results since my contrast agent bolus would "jump over" some grid-elements then... Thank you for all your help and ideas, Lilly |
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May 2, 2012, 05:21 |
CFL-number
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#2 |
Senior Member
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Sorry, I meant CFL-number, of course!
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May 2, 2012, 09:50 |
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#3 | |
Senior Member
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
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Quote:
You only need to focus on CFL number for the explicit time-stepping. For implicit time-stepping (stability is guaranteed). The way implicit time-stepping scheme is handled in Fluent it is dummyproof (as there are iterations in-between) and you can do iterations as large as you like. For explicit time-stepping you will have both of the problems you mentioned: 1) stability and 2) the case of grid jumping so CFL number is very important. That said, maintaining the proper CFL number even for the implicit time-stepping helps drastically to improve its convergence at each time-step. |
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May 4, 2012, 10:54 |
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#4 |
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Thank you for your helpful explanation LuckyTran!
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