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-   -   How to solve Poisson equation in CFX 4? (http://www.cfd-online.com/Forums/cfx/20114-how-solve-poisson-equation-cfx-4-a.html)

windhair January 19, 2004 18:45

How to solve Poisson equation in CFX 4?
 
Hi, all I want to solve a semi-Poisson equation for a user scalar, it is in the form: D^2(PHI)/DX^2 + D^2(PHI)/DY^2 = f(PHI). Because the right term is a function of scalar PHI, it may cause some converge problem as I think, how to make this works in CFX 4.4 by command file or by user subroutine? aks for help. Thanks

Jeff January 19, 2004 22:49

Re: How to solve Poisson equation in CFX 4?
 
This is just a diffusion equation with a linear source. Turn off convection (NO CONVECTION under the diffusion scheme) and set your source coeffient in the SP term which will be multiplied by PHI by the solver.

This has been done to solve for electric fields.

Jeff

windhair January 20, 2004 04:29

Re: How to solve Poisson equation in CFX 4?
 
OK, thanks, it work for SUM[AM(PHI_P-PHI_M)] = S_U + S_P *PHI_P, but if the right side is not simply S_P * PHI_P but a function of PHI, for example EXP(PHI), is there any differency?

Jeff January 27, 2004 22:09

Re: How to solve Poisson equation in CFX 4?
 
Depending on the form of the expression, separate any terms out that are multiplied by just PHI, and put those into S_P. Evaluate everything else (including functions of PHI) and assign it to S_U. The more you can put into S_P the better (see documentation on linearization of sources).

Jeff


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