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pipe with orifice, pressure drop declines when pipe gets longer (BC problem?) |
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January 21, 2016, 05:55 |
pipe with orifice, pressure drop declines when pipe gets longer (BC problem?)
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Christof Schmidt
Join Date: Nov 2015
Posts: 6
Rep Power: 11 |
Hi everybody,
I hope anybody can help me out with my case. Iīve got a pipe with an orifice in it. Inlet is on the left and outlet on the right side. I have a turbulence air flow solving with simple foam and want to calculate the pressure drop between Inlet and Outlet. Inlet: internalField uniform (0 0 0); boundaryField { inlet_solid { type fixedValue; value uniform (4.63 0 0); } outlet_solid { type zeroGradient; } walls_solid { type fixedValue; value uniform (0 0 0); } Outlet: internalField uniform 0; boundaryField { inlet_solid { type zeroGradient; } outlet_solid { type fixedValue; value uniform 0; } walls_solid { type zeroGradient; } two cases (attached pictures): 1. short pipe 2. the second pipe is longer after the orifice The problem is that I get a fewer pressure drop for the longer pipe. short pipe: dp=63.5 Pa long pipe: dp=53.5 Pa short pipe: I assume that the problem is the boundary condition p=0 at the outlet. Perhaps that condition conflicts with the "chaotic" flow profile at the outlet. long pipe: in that case the flow at the outlet "calmed down". (so I think value of pressure drop more plausible for that case) How can I change the boundary conditions to get a more accurate value for the pressure drop for the short pipe (if thatīs the reason)? I thought about to work with the type calculated for the pressure at the outlet |
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