Calculating Pressure Drop - BCs

spoon · February 25, 2013, 17:27

Hi,

I am trying to simulate flow over an obstruction in a pipe in order to calculate pressure drop across the pipe. I know the flopw rate through the pipe and I also know that nominally the inlet pressure is 100 Pa.

I am not sure how to go about setting up my boundary conditions for this calculation.

At the moment my toughts are:
Pressure:
Inlet - Fixed Value
Outlet - zeroGradient (??)
Walls - zeroGradient

Velocity:
Inlet - fixed value
outlet - inletOutlet with inletValue (0 0 0), not sure what Value option should be here
walls - fixedValue Uniform (0 0 0)

Does this seem correct? I have not done CFD in quite a while now so can't really remember.

I am also wondering the best way to calculate the actual total pressure drop.... Any suggestions here?

Thanks

NickolasPl · February 25, 2013, 19:47

Hello,

Well if you specifiy the pressure and the velocity at the same boundary it is like you re overdefining your problem. As you have a purely pressure driven flow I suggest to specify zero pressure at the exit and flow rate/velocity at the inlet boundary along with no slip at the walls. Since you know the pressure drop as you say, the software then should calculate the flowrate so that to preserve the mass balance.

Regards,

Nickolas

February 25, 2013, 17:27	Calculating Pressure Drop - BCs	#1
spoon New Member Join Date: Mar 2012 Posts: 2 Rep Power: 0	Hi, I am trying to simulate flow over an obstruction in a pipe in order to calculate pressure drop across the pipe. I know the flopw rate through the pipe and I also know that nominally the inlet pressure is 100 Pa. I am not sure how to go about setting up my boundary conditions for this calculation. At the moment my toughts are: Pressure: Inlet - Fixed Value Outlet - zeroGradient (??) Walls - zeroGradient Velocity: Inlet - fixed value outlet - inletOutlet with inletValue (0 0 0), not sure what Value option should be here walls - fixedValue Uniform (0 0 0) Does this seem correct? I have not done CFD in quite a while now so can't really remember. I am also wondering the best way to calculate the actual total pressure drop.... Any suggestions here? Thanks

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February 25, 2013, 19:47		#2
NickolasPl Member Nickolas P Join Date: Oct 2010 Location: Greece Posts: 30 Rep Power: 16	Hello, Well if you specifiy the pressure and the velocity at the same boundary it is like you re overdefining your problem. As you have a purely pressure driven flow I suggest to specify zero pressure at the exit and flow rate/velocity at the inlet boundary along with no slip at the walls. Since you know the pressure drop as you say, the software then should calculate the flowrate so that to preserve the mass balance. Regards, Nickolas