How should I implement this scalar transport equation

sharonyue · April 14, 2014, 09:38

Hi guys,

I wanna solve this equation:
$\frac{{\partial j}}{{\partial t}} + \nabla \cdot \left( {jU} \right) = {C_1} \cdot f\left( \varepsilon \right) \cdot j - {C_2} \cdot \varphi \left( \varepsilon \right) \cdot {j^{\frac{{11}}{9}}}$

I code it like this:

Code:

    fvScalarMatrix nEqn
    (
	    fvm::ddt(j)   
       +   fvm::div(phi1,j)
           ==
	   C1*j* epsilon
	  -fvm::Sp(C2*pow(j, 2.0/9.0)* epsilon, j)
    );

But it's result is wired. Thanks in advance.

bieshuxuhe · April 14, 2014, 21:32

hello!

maybe you could give more information , for example:
C1>0 or C1<0, epsilon?

sharonyue · April 14, 2014, 21:37

Quote:

Originally Posted by bieshuxuhe

hello!

maybe you could give more information , for example:
C1>0 or C1<0, epsilon?

C1, C2, epsilon is all positive~ can I deal with this with some sophisticated approach?

bieshuxuhe · April 14, 2014, 22:53

I suppose that :
1 "j+jSmall" is "j"
2 there is no limit of the value of "j"

then , modify the source term " -C2*pow((j+jSmall),11.0/9.0)* epsilon " to :

Code:

- 11.0/9.0*C2*fvm::Sp(epsilon,j) 
+ 2.0/9.0*C2*epsilon*pow(j,11.0/9.0)

maybe this will be fine!
of cource maybe there is some other reason for wired result, not only the discretization of source term.

April 14, 2014, 09:38	How should I implement this scalar transport equation	#1
sharonyue Senior Member Dongyue Li Join Date: Jun 2012 Location: Beijing, China Posts: 838 Rep Power: 17	Hi guys, I wanna solve this equation: $\frac{{\partial j}}{{\partial t}} + \nabla \cdot \left( {jU} \right) = {C_1} \cdot f\left( \varepsilon \right) \cdot j - {C_2} \cdot \varphi \left( \varepsilon \right) \cdot {j^{\frac{{11}}{9}}}$ I code it like this: Code: fvScalarMatrix nEqn ( fvm::ddt(j) + fvm::div(phi1,j) == C1j epsilon -fvm::Sp(C2pow(j, 2.0/9.0) epsilon, j) ); But it's result is wired. Thanks in advance. Last edited by sharonyue; April 14, 2014 at 21:55.

April 14, 2014, 22:53		#4
bieshuxuhe Member xuhe-openfoam Join Date: Aug 2013 Location: DaLian，china Posts: 82 Rep Power: 12	I suppose that : 1 "j+jSmall" is "j" 2 there is no limit of the value of "j" then , modify the source term " -C2pow((j+jSmall),11.0/9.0) epsilon " to : Code: - 11.0/9.0C2fvm::Sp(epsilon,j) + 2.0/9.0C2epsilon*pow(j,11.0/9.0) maybe this will be fine! of cource maybe there is some other reason for wired result, not only the discretization of source term.

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April 14, 2014, 21:32		#2
bieshuxuhe Member xuhe-openfoam Join Date: Aug 2013 Location: DaLian，china Posts: 82 Rep Power: 12	hello! maybe you could give more information , for example: C1>0 or C1<0, epsilon?