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Old   May 9, 2004, 16:57
Default about the discretization of unsteady term
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I have question for the unsteady methods.

one is three time level method, another is Adam-bashforth methos. Usually, the most of LES is using the adams-bashforth method for the convection terms and the Crank-Bicolson for the diffusion term.

I'm making code for LES using three-time level method(SIMPLE scheme is used)

What's the difference three time level and Adam-Bashforth ones?

Does have any problems if I use the three time level methd in SIMPLE for LES code?

If it is wrong, How to apply the adams-bashforth method to SIMPLE scheme?

Thank you for your concerned

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Old   May 10, 2004, 12:01
Default Re: about the discretization of unsteady term
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Crank Nicholson is a single step implicit scheme.

Adams Bashforth is a multi-step scheme, which reads as,

u_n+1 = u_n + 1/2*(3*u_n - u_n-1)

I don't know what is a three time level scheme. Most likely, it is a three step scheme (possibly BDF) or a three stage Runge Kutta, (which can be second order accurate at best).

You can find details of such schemes in any numerical book on ODEs. I recommend: E Hairer, SP Norsett and G Wanner, Solving ordinary differential equations, second edition (2 vols.). But it may be too advanced for beginers.

Hope this helps.
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