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divergence of Poisson equation

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Old   January 6, 2007, 05:19
Default divergence of Poisson equation
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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
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Old   January 6, 2007, 07:28
Default Re: divergence of Poisson equation
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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)
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Old   January 8, 2007, 13:06
Default Re: divergence of Poisson equation
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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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