Different results with different Boundary conditions

ravi1650 · June 3, 2009, 09:40

Hi,

I am simulating a single phase laminar flow in a pipe in 3d geometry.
When I put the inlet condition as pressure condition, I get an error of 15%(for Re=500), when compared with the analytical solution. The error increases with increase in Reynold's number .
But when I put the inlet condition as velocity inlet(corresponding to Re or pressure drop), I get an error of just <1% (accurate result).
Can you tell me what there is so much difference in results with slight change in the defination of boundary conditions.

ravi1650 · June 3, 2009, 10:25

Is it the reason that FLUENT uses different computational schemes for different inlet boundary conditions?
or
FLUENT is highly sensitive to the choice of B.C to be selected to arrive at accurate result?

Please explain, when can I use velocity inlet as inlet B.C and pressure inlet as inlet B.C ?

Is there anything else( other than the inlet Pressure value) to be defined in case of pressure inlet as inlet B.C ??

Please help!!!

June 3, 2009, 09:40	Different results with different Boundary conditions	#1
ravi1650 New Member Ravi Kapoor Join Date: May 2009 Posts: 6 Rep Power: 17	Hi, I am simulating a single phase laminar flow in a pipe in 3d geometry. When I put the inlet condition as pressure condition, I get an error of 15%(for Re=500), when compared with the analytical solution. The error increases with increase in Reynold's number . But when I put the inlet condition as velocity inlet(corresponding to Re or pressure drop), I get an error of just <1% (accurate result). Can you tell me what there is so much difference in results with slight change in the defination of boundary conditions.

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June 3, 2009, 10:25		#2
ravi1650 New Member Ravi Kapoor Join Date: May 2009 Posts: 6 Rep Power: 17	Is it the reason that FLUENT uses different computational schemes for different inlet boundary conditions? or FLUENT is highly sensitive to the choice of B.C to be selected to arrive at accurate result? Please explain, when can I use velocity inlet as inlet B.C and pressure inlet as inlet B.C ? Is there anything else( other than the inlet Pressure value) to be defined in case of pressure inlet as inlet B.C ?? Please help!!!