Fixed Flow rate and outlet Continuity Problem

mrshb4 · March 9, 2012, 14:18

Dear Foamers,

I'm modeling a centrifugal fan in a fix flow rate with OF, but I had a problem and haven't find any solution for it!!!!

As I know in fluent it is modeled by these BCs:

inlet: massFlowRate

outlet: outflow

in OF I've tested many things like:

inlet: U: fixedFlowRate
p: fixedFluxPressure/zeroGradient

outlet: U: zeroGradient/fluxCorrectedVelocity
p: zerGradient

and a pRefCell and pRefValue for pressure reference. I think these Bcs are equivalent as the Fluent Bcs. When I run the MRFSimpleFoam the error would be

Continuity error cannot be removed by adjusting the outflow.
Please check the velocity boundary conditions and/or run potentialFoam to initialise the outflow.
Total flux : 56.788705
Specified mass inflow : 0.55
Specified mass outflow : 0
Adjustable mass outflow : 0

What is the problem? Thanks for your help.!!!

calim_cfd · March 10, 2012, 14:32

when you use a fixedflowrate type for bcs.. you cannot constraint the outlet else you'll get this error...enforcing zerograd on U does it..try using inletout types with massflow types.. cuz then u can have backflow

or convert your massflow to velocity and use, if possible :
inlet

Code:

u=fixedvalue
p=zerograd

outlet

Code:

u=zerograd
p=fixedvalue

see if it works

March 9, 2012, 14:18	Fixed Flow rate and outlet Continuity Problem	#1
mrshb4 Member Mohammad.R.Shetab Join Date: Jul 2010 Posts: 49 Rep Power: 15	Dear Foamers, I'm modeling a centrifugal fan in a fix flow rate with OF, but I had a problem and haven't find any solution for it!!!! As I know in fluent it is modeled by these BCs: inlet: massFlowRate outlet: outflow in OF I've tested many things like: inlet: U: fixedFlowRate p: fixedFluxPressure/zeroGradient outlet: U: zeroGradient/fluxCorrectedVelocity p: zerGradient and a pRefCell and pRefValue for pressure reference. I think these Bcs are equivalent as the Fluent Bcs. When I run the MRFSimpleFoam the error would be Continuity error cannot be removed by adjusting the outflow. Please check the velocity boundary conditions and/or run potentialFoam to initialise the outflow. Total flux : 56.788705 Specified mass inflow : 0.55 Specified mass outflow : 0 Adjustable mass outflow : 0 What is the problem? Thanks for your help.!!!

March 10, 2012, 14:32		#2
calim_cfd Senior Member mauricio Join Date: Jun 2011 Posts: 172 Rep Power: 17	when you use a fixedflowrate type for bcs.. you cannot constraint the outlet else you'll get this error...enforcing zerograd on U does it..try using inletout types with massflow types.. cuz then u can have backflow or convert your massflow to velocity and use, if possible : inlet Code: u=fixedvalue p=zerograd outlet Code: u=zerograd p=fixedvalue see if it works __________________ Best Regards /calim "Elune will grant us the strength"

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