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August 5, 2018, 08:40 |
CFL at CFX
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#1 |
New Member
Mentzos
Join Date: Dec 2010
Location: Athens
Posts: 22
Rep Power: 15 |
Hi
My question is that: as the implicit scheme is unconditionally stable for any size of time step and the transient scheme of CFX are implicit what the meaning CFL |
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August 5, 2018, 09:12 |
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#2 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
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Stability: see https://flow3d.com/resources/cfd-101...rical-methods/
CFL: https://en.wikipedia.org/wiki/Couran...Lewy_condition Google is your friend.
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August 5, 2018, 09:30 |
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#3 |
New Member
Mentzos
Join Date: Dec 2010
Location: Athens
Posts: 22
Rep Power: 15 |
Thanks for your reply.
But as i wrote from "W. Malalasekera and Versteeg" the implicit scheme (as of CFX) UNCONDITIONALLY STABLE....or better "not require the Courant number to be small but but neither very big... eg 100" |
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August 5, 2018, 20:05 |
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#4 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
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Rep Power: 144 |
That is correct. In terms of numerical stability of the time step scheme implicit schemes are unconditionally stable. Instead the maximum time step size is determined by how accurately the numerical scheme can follow the modelled transients. Note that if the scheme cannot follow the modelled transients accurately that this is can lead to numerical instability - but this is a different form of instability to that related directly to the time step size. This is discussed in more detail in the link I posted (and Malalasekera and Versteeg probably discuss it as well).
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