Continuity between Inlet and Outlet

hebe03364 · January 10, 2019, 09:11

Hello,

i just want to generally ask if there is a possibility to apply a boundary condition for the outlet that is able to maintain continuity concerning a given inlet boundary condition? What I mean is, that I specified a certain velocity for the inlet and I want a boundary condition that automatically computes the corresponding velocity for the outlet, so that the mass flow is constant.

Thanks in advance!

clapointe · January 10, 2019, 17:22

Yes there is. Check this one out : https://github.com/OpenFOAM/OpenFOAM...hVectorField.H.

Caelan

hebe03364 · January 23, 2019, 04:47

Thank you very much Caelan!

time- · February 26, 2019, 18:53

Thanks for the hint Caelan.
What about p field in this case? Should be set to zeroGrandient for all patches?
Any particular advise?

Bye

clapointe · February 28, 2019, 08:49

My first guess is that this might work bc the incompressible solvers always set a reference pressure (usually zero) somewhere in the domain. I would try it to make sure.

Caelan

hebe03364 · February 28, 2019, 09:45

I think so too, just use zeroGradient for the inlet and the outlet and it should work. I also did that.

Greets hebe03364

Eldrael · March 7, 2019, 21:20

Quote:

Originally Posted by hebe03364

I think so too, just use zeroGradient for the inlet and the outlet and it should work. I also did that.

Greets hebe03364

Hello hebe:

I am not sure whether zeroGradient is a "physical" boundary condition. If I understood correctly, you want some kind of cyclic boundary condition that keeps continuity in an integral sense. Then, the pressure gradient should be somehow given by the flow conditions rather than imposed.

I have not tried it, but fixedFluxPressure should calculate pressure gradient according to the velocity condition: https://github.com/OpenFOAM/OpenFOAM...hScalarField.H

If this does not work you might want to run

HTML Code:

simpleFoam -listScalarBCs

to see more BCs.

Bodo1993 · January 13, 2020, 10:12

Dear All,

Greetings. I was wondering if the matchedFlowRateOutletVelocity would avoid the problems of backflow at the outlet boundary.

Also, I use twoLiquidMixingFoam multiphase solver, what would be a compatible phase boundary condition?

Please let me know if I should provide more details for my simulation case.

Thanks.

January 10, 2019, 09:11	Continuity between Inlet and Outlet	#1
hebe03364 New Member Bernhard Join Date: Jun 2018 Posts: 15 Rep Power: 7	Hello, i just want to generally ask if there is a possibility to apply a boundary condition for the outlet that is able to maintain continuity concerning a given inlet boundary condition? What I mean is, that I specified a certain velocity for the inlet and I want a boundary condition that automatically computes the corresponding velocity for the outlet, so that the mass flow is constant. Thanks in advance!

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January 10, 2019, 17:22		#2
clapointe Senior Member Join Date: Aug 2015 Posts: 494 Rep Power: 14	Yes there is. Check this one out : https://github.com/OpenFOAM/OpenFOAM...hVectorField.H. Caelan

January 23, 2019, 04:47		#3
hebe03364 New Member Bernhard Join Date: Jun 2018 Posts: 15 Rep Power: 7	Thank you very much Caelan!

February 26, 2019, 18:53		#4
time- New Member Mattia Join Date: May 2018 Location: Novara - Italy Posts: 29 Rep Power: 7	Thanks for the hint Caelan. What about p field in this case? Should be set to zeroGrandient for all patches? Any particular advise? Bye

February 28, 2019, 08:49		#5
clapointe Senior Member Join Date: Aug 2015 Posts: 494 Rep Power: 14	My first guess is that this might work bc the incompressible solvers always set a reference pressure (usually zero) somewhere in the domain. I would try it to make sure. Caelan

February 28, 2019, 09:45		#6
hebe03364 New Member Bernhard Join Date: Jun 2018 Posts: 15 Rep Power: 7	I think so too, just use zeroGradient for the inlet and the outlet and it should work. I also did that. Greets hebe03364

January 13, 2020, 10:12		#8
Bodo1993 Senior Member Join Date: Jul 2019 Posts: 148 Rep Power: 6	Dear All, Greetings. I was wondering if the matchedFlowRateOutletVelocity would avoid the problems of backflow at the outlet boundary. Also, I use twoLiquidMixingFoam multiphase solver, what would be a compatible phase boundary condition? Please let me know if I should provide more details for my simulation case. Thanks.