# divergence of Poisson equation

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 January 6, 2007, 05:19 divergence of Poisson equation #1 dusky.he Guest   Posts: n/a Does anyone can tell me the possible reason of divergence when solving Poisson equation? I am using projection method to simulate the bubble growth. I guess the proble is the outlet boundary condtion. Anyone can tell me? Thanks in advance

 January 6, 2007, 07:28 Re: divergence of Poisson equation #2 rt Guest   Posts: n/a if u have velosity inlet and your fluid is incompressible, u must take care for your outlet bc, as u must impose it so the net flux be zero, so your guess is correct and in/out bc can be source of divergence. As a cure i recoomend to use pressure boundary condition as outlet boundary condition, dirichlet bc (note that solution of poisson eq. with completely newmann bc is problematic, sometimes can't unique solution theoritically)

 January 8, 2007, 13:06 Re: divergence of Poisson equation #3 rt Guest   Posts: n/a addingn to previous comment if u use variable density method, with increasing density ratio the condition number of poisson equation is increased (ill-poseness is increased), so u must increase power of your linear solver if it is iterative (number of essential interations is increased with increasing density ratio) u can change density ratio and study this. in my experience, simple SOR is not sufficient for density ration 1000, but ICCG (or ILU+GMRES) is good.

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