# Poisson BC's

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 May 17, 2001, 16:47 Poisson BC's #1 Peter Guest   Posts: n/a Hi to all, while trying to implement the pressure equation (Poisson) and enforce continuity in order to solve the incompressible Euler equations a choice on the boundary conditions type must be done. Either Dirichlet or Neumann, what it is for sure is that BC's for the pressure must be prescribed in all the borders of the domain of study. But this is not the same for the fluid-dynamic problem, one must prescribe conditions at the inlet with care (and not to overspecify the problem) without knowing what it is happening downstream. My question is: How can one specify BC's to solve Poisson equation at all borders without knowing the solution of the fluid-dynamic problem??? Any help will be good Peter

 May 17, 2001, 18:20 Re: Poisson BC's #2 Seb Guest   Posts: n/a The BC's for pressure depend on the ones you use for the normal velocity. When the normal velocity is imposed (at a wall or at the inlet), a Neumann BC prevails for the pressure. When the velocity (or mass flow) is free, a dirichlet BC is imposed to the pressure (usualy it is at an outlet). Now, depending on the projection method you use (SIMPLE, SIMPEC, SIMPLER, Chorin projection-1, Chorin's projections-2....), the NEUMAN BC for the pressure (or correction of pressure) as to be such that the velocity at the end of the time step will be divergence free. For more info on pressure BC's, you should look for some of the books written by Grasho and Sani.