Difference between revisions of "HowTo Adding a new transport equation"

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</cpp>
 
</cpp>
  
In this example, the source term is treted explicitly. To manage it implicitly, OpenFOAM provides the <tt>Sp</tt> and the <tt>SuSp</tt> functions.
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In this example, the source term is treated explicitly. To manage it implicitly, OpenFOAM provides the <tt>Sp</tt> and the <tt>SuSp</tt> functions.
Suppose to write it as <math>S_k = \Kappa \psi </math>. The code lines to solve the same equation with an implicit treatment of the source term are:
+
Suppose we can write it as <math>S_k = \Kappa \psi </math>. The code lines to solve the same equation with an implicit treatment of the source term are:
  
 
<cpp>
 
<cpp>
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   - fvm::laplacian(gamma, psi)
 
   - fvm::laplacian(gamma, psi)
 
   ==
 
   ==
     Su(kappa, psi)
+
     fvm::Sp(kappa, psi)
 
);
 
);
 
</cpp>
 
</cpp>
  
 
<tt>SuSp(kappa, psi)</tt> can be used to discretise the source term implicitly or explicitly according to the sign of <tt>kappa</tt>.
 
<tt>SuSp(kappa, psi)</tt> can be used to discretise the source term implicitly or explicitly according to the sign of <tt>kappa</tt>.
 +
 +
[[Category:Tutorials]]

Latest revision as of 11:13, 21 October 2013

Suppose you want to solve and additional scalar transport equation for the scalar \psi by adding it to an existing solver. The equation has the form

\frac{\partial}{\partial t} \left(\rho \psi \right) + \nabla \cdot \phi \psi - \nabla \cdot \Gamma \nabla \psi = S_{\psi}

where \rho and \Gamma are defined as dimensionedScalar and are retrieved from a dictionary using the lookup member function. S_{\phi} is the source term.

To implement the equation, just add the line:

dimensionedScalarField psi;

to the createFields.H file of the solver,

Then, solve the equation by adding the following lines in the point of the solver where you want the equation to be solved.

 
solve
(
    fvm::ddt(rho, psi)
  + fvm::div(phi, psi)
  - fvm::laplacian(gamma, psi)
  ==
    S_psi
);

In this example, the source term is treated explicitly. To manage it implicitly, OpenFOAM provides the Sp and the SuSp functions. Suppose we can write it as S_k = \Kappa \psi . The code lines to solve the same equation with an implicit treatment of the source term are:

 
solve
(
    fvm::ddt(rho, psi)
  + fvm::div(phi, psi)
  - fvm::laplacian(gamma, psi)
  ==
    fvm::Sp(kappa, psi)
);

SuSp(kappa, psi) can be used to discretise the source term implicitly or explicitly according to the sign of kappa.