Adding source term involving derivative in y direction

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 February 22, 2013, 13:51 Adding source term involving derivative in y direction #1 New Member   Sohail Join Date: Mar 2012 Posts: 11 Rep Power: 7 Hi everyone, I want to add a new transport equation to simpleFoam. The source term looks like Sw = nu/pow(y,2) * dw/dy where y is the y-coordinate of the cell and dw/dy is the derivative in the y-direction. fvScalarMatrix UwEqn ( fvm::div(phi, w) - fvm::laplacian(nu, w) - Sw ); My confusion is to get the derivative in a one direction not to calculate the whole gradient. Can anybody give me an idea how to achieve this. regards, Sohail

 February 22, 2013, 15:10 #2 Senior Member   Mahdi Hosseinali Join Date: Apr 2009 Location: NB, Canada Posts: 271 Rep Power: 11 If i'm correct you may get the gradient only in the explicit way which would be: vectorField gradU=fvc::grad(w) then you can extract the desired component by: scalarField dwdy=gradU.component(vector::Y) I may not be correct in spelling or own the best way, but this should work

 February 24, 2013, 09:31 #3 New Member   Sohail Join Date: Mar 2012 Posts: 11 Rep Power: 7 Dear Hosseinali, Thankyou for giving time to answer. I also thought the same and it works fine. But now I have another problem. I have a term Sw = (Uy * w)/y where Uy is the y component of velocity and y coordinate. Can this term be put in UwEqn as, fvm::Sp(Uy/y, w) where Uy=U.component(vector::Y) Best regards, Sohail

 February 25, 2013, 05:20 #4 Senior Member   Mahdi Hosseinali Join Date: Apr 2009 Location: NB, Canada Posts: 271 Rep Power: 11 Just from the top of my head, when you are using the SIMPLE every equation is being solved separately, also in source term of your equation for UwEqn there is no Uw (Uy is being considered known from previous step) so I think there would be no difference if you use fvm or mention it explicitly

February 25, 2013, 10:30
#5
New Member

Sohail
Join Date: Mar 2012
Posts: 11
Rep Power: 7
Dear Hosseinali,

I tried to put the term

Sw = (Uy * w)/y

with fvm::Sp and explicitely. but in both cases the value of Sw tends to infinity
after 500 iterations approximately.

I am using OpenFOAM-1.6-ext. I am simulating a 2D axisymmetric case.
Where this new transport equation calculates the swirl-component
of velocity.

Please have a look at the file.
If you want the whole case file, I can also send you that...

regards,

Sohail
Attached Files
 wEqn.H (637 Bytes, 14 views)

Last edited by iqbalsk8; February 25, 2013 at 11:48.

 March 2, 2013, 11:39 #6 Senior Member   Mahdi Hosseinali Join Date: Apr 2009 Location: NB, Canada Posts: 271 Rep Power: 11 I'm not sure how this affects your stability, All I'm saying is that with the solver you chose this term would have same effect explicitly or implicitly on the solution.

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