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Why sovle e p U but not T p U in sonicFoam?

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Old   July 16, 2010, 09:43
Default Why sovle e p U but not T p U in sonicFoam?
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yu
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Hi, I am just curious why variable solved in sonicFoam are e p U. Then, calcualte T using function

inline scalar T (scalar f, scalar T0, scalar (specieThermo::*F)(const scalar) const, scalar (specieThermo::*dFdT)(const scalar) const ) const

of class specieThermo.

What is the benifit comparing to solve T p U.


Thanks, yu.
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Old   July 19, 2010, 08:11
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Stefan Herbert
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Hi Yu,

I think it is easier to include temperature-dependent thermodynamic properties (especially the heat capacity) when solving for e instead of T.

Regards,
Stefan
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Old   July 19, 2010, 08:28
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yu
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Stefan,

Thank you for your reply.

I agree. It will make a implict couple between heat capacity and temperature.

Is that possible that solving e will give more smoother result than solving T? So, solving e will be more numerically stable>

Thanks

Yu

Quote:
Originally Posted by herbert View Post
Hi Yu,

I think it is easier to include temperature-dependent thermodynamic properties (especially the heat capacity) when solving for e instead of T.

Regards,
Stefan
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Old   July 19, 2010, 16:25
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I guess that there are several difficulties to solve T instead of e.

1, solving e is to solve Cv*T, but involves only one variable, which makes code easier.

2, in openfoam, solving Cv*T is not straight forward. I tried different ways to put Cv in the equation, this one works,

{
solve
(
Cv*fvm::ddt(rho, T)
+ Cv*fvm::div(phi, T)
- Cv*fvm::laplacian(turbulence->alphaEff(), T)
==
- p*fvc::div(phi/fvc::interpolate(rho))
);
}

However, it separate Cv and T, and make the scheme less accurate.
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