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Old   August 5, 2018, 07:40
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Mentzos
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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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Old   August 5, 2018, 08:12
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Stability: see https://flow3d.com/resources/cfd-101...rical-methods/

CFL: https://en.wikipedia.org/wiki/Couran...Lewy_condition

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Old   August 5, 2018, 08:30
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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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Old   August 5, 2018, 19:05
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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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