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

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 July 16, 2010, 09:43 Why sovle e p U but not T p U in sonicFoam? #1 New Member   yu Join Date: Nov 2009 Posts: 26 Rep Power: 8 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.

 July 19, 2010, 08:11 #2 Senior Member   Stefan Herbert Join Date: Dec 2009 Location: Darmstadt, Germany Posts: 129 Rep Power: 9 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

July 19, 2010, 08:28
#3
New Member

yu
Join Date: Nov 2009
Posts: 26
Rep Power: 8
Stefan,

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 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

 July 19, 2010, 16:25 #4 New Member   yu Join Date: Nov 2009 Posts: 26 Rep Power: 8 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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