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source term linearization

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Old   October 10, 2001, 13:03
Default source term linearization
  #1
sivakumar
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hello,

i have source term of the form

Sphi = a-b*phi^2

as we can see it is non linear in terms of phi and this is affecting the convergence. fluent suggests that i use a linearized form as follows,

Sphi = a+(-b)*phi

can any one please help me with the linearization of this term to the fluent form. any help(references/techniques) would be greatly appreciated. Thanks in advance.
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Old   October 16, 2001, 17:04
Default Re: source term linearization
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Ugur
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You can try to use Taylor Expansion, and just consider the linear term.
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Old   October 23, 2001, 12:50
Default Re: source term linearization
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sivakumar
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hi ugur,

if i use the taylor sereis expansion how would i be able to use it in FLUENT? the expansion would be of the form,

f(Sphi) = Sphio+(dSphi/dphi)*(phi-phio); how will i be able to get the previous value of phi(i.e phio)? thanks for the help, siva.
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Old   October 23, 2001, 15:38
Default Re: source term linearization
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Ugur
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Actually, what has been said is, you don't have to linearize. What you can do is write your source term in the form that you have as source, and the first derivative of the source term wrt the variable dS[eqn].
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