# Using compressible BCs for incompressible problems

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 April 9, 2006, 01:07 Using compressible BCs for incompressible problems #1 cfd Guest   Posts: n/a Hello ppl, I'm trying to formulate the flow past a block in an open domain. I've a fractional step scheme on hand and I'm using the finite volume method. I've used it to test Ghia's lid driven cavity and results are very similar. I believe I just need to modify the boundary conditions (BCs) for my new problem. I was reading Blazark's CFD book and these are the BCs given for subsonic inflow and outflow (mine is an incompressible problem) For inflow a belongs to outside of domain, b is on the boundary, d is inside domain. a .... b .... d p(b)=0.5*{p(a)+p(d)-rho(0)*c(0)*[nx*(u(a)-u(d))+ny*(v(a)-v(d))]} rho(b)=rho(a)+(rho(b)-rho(a))/c(0)^2 u(b)=u(a)nx*(p(a)-p(b))/(rho(0)*c(0)) v(b)=v(a)nx*(p(a)-p(b))/(rho(0)*c(0)) rho(0) & c(0) represents reference state For outflow a belongs to outside of domain, b is on the boundary, d is inside domain. d .... b .... a p(b)=p(a) rho(b)=rho(d)+(rho(b)-rho(d))/c(0)^2 u(b)=u(d)nx*(p(d)-p(b))/(rho(0)*c(0)) v(b)=v(d)nx*(p(d)-p(b))/(rho(0)*c(0)) p(a)=prescribed static pressure So, is this BCs applicable since this is an incompressible problem? Also in most problems, ppl usually specify inlet velocity (e.g. u=1,v=0). Is there a need to specify pressure at inlet as well?

 April 16, 2006, 02:41 Re: Using compressible BCs for incompressible prob #2 Harish Guest   Posts: n/a When you specify velocity you do not usually specify pressure.Have a look at peric and ferziger for more details. -H

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