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-   -   Negative values of concentration while solving temperature (http://www.cfd-online.com/Forums/openfoam-solving/57979-negative-values-concentration-while-solving-temperature.html)

sachin February 9, 2009 01:42

Hi Vishal, I m not sure but j
 
Hi Vishal,
I m not sure but just a suggestion are your boundary conditions correct
or check your domain if it is too complex.... try to simplify... if that works fine....reduce the grid size (inc no. of grid pts)and reduce time step size
I think the equations would be making solution quite unstable
Though I m not sure...just some suggestions
Hope you find the error http://www.cfd-online.com/OpenFOAM_D...part/happy.gif
Regards
Sachin

sachin February 9, 2009 03:13

Hi Vishal, I guess these are
 
Hi Vishal,
I guess these are to stringent BC's may be they reach at some point where they dont satisfy them correctly
My suggestion - for outlet just extrapolate the values by zerogradient...chk result...if this doesnt work ... http://www.cfd-online.com/OpenFOAM_D...part/happy.gif...i hope it does
Dont modify the whole set at time....modify B.C's one by one ...try modify only for Phi then for C1 then for C2 ...see if u can get descent results no absurd values...if this also fails change one boundary everytime and run ...might find why it fails...I know this sounds wierd...http://www.cfd-online.com/OpenFOAM_D...part/happy.gif
Just one more question are you very sure of the eq you have discretised...i mean u have separated phi from conc ..ok but after they recombine do they give the equations back
Sachin

nandiganavishal February 9, 2009 03:39

Hi Sachin, Thanks for the r
 
Hi Sachin,

Thanks for the response.. I would try them.. and would get back to you...


The exact equations which I would like to solve are

div {(D1*grad(C1) + D1*Z1*C1*grad(Phi))} = 0 -(1)
div {(D2*grad(C2) + D2*Z2*C2*grad(Phi))} = 0 -(2)
laplacian (phi) = - alpha * Z1*C1 - alpha*Z2 * C2 - (3)

where C1 C2 and Phi are concentrations and potential respectively and D1,D2,Z1,Z2, alpha are constants

Regards

Vishal


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