Problem with BC: Setting a pressure for Inlet

McCharles · July 1, 2016, 05:42

Hello Foamers,

I succesfully calculated a case with rhoSimplecFoam with the following BC:

INLET patch :
- for U : flowRateInletVelocity (massFlowRate)
- for p : zeroGradient
- for T : fixedValue

OUTLET patch :
- for U : pressureInletOutletVelocity
- for p : fixedValue
- for T : zeroGradient

The results are looking good but as OpenFoam calculates the pressure at the Inlet, there is a small difference with my experimental results at this location.

Now I want to try it the other way around by setting the pressure at the Inlet and defining a mass Flow at the Outlet. Unfortunately, with this setup, the calculation blows up after 1 iteration. These were the settings:

INLET Patch:
- for U : pressureInletVelocity
- for p : fixedValue
- for T : zeroGradient

Outlet Patch :
- for U : flowRateInletVelocity
- for p : outletInlet (There is a recirculation in this Area of the Domain)
- for T : inletOutlet

I would be very thankful if someone could give me a hint on how to fix my problem. What is wrong with my BC? I'm wondering if it is actually possible to set up a case by defining an Inlet pressure.

Cheers,

Charles

TobM · July 1, 2016, 07:54

Two thoughts:
Is it important for you to define the mass flow rate at the outlet? Try it at the inlet.
In most cases, you use a totalPressure BC at the inlet. Would this be an option?

McCharles · July 1, 2016, 08:49

Quote:

Originally Posted by TobM

Two thoughts:
Is it important for you to define the mass flow rate at the outlet? Try it at the inlet.
In most cases, you use a totalPressure BC at the inlet. Would this be an option?

Hi TobM and thanks for your suggestion,

Concerning the Mass Flow, I have to define it somewhere and if I set the pressure at the Inlet, I can't also define the massFlow there as OpenFoam always needs a certain degree of freedom. That's why I defined the mass flow at the outlet.

Using totalPressure is a good ideal, I will try it out.

TobM · July 1, 2016, 09:37

MassFlowRate, totalpressure and totalTemperature at inlet are common BCs. Of course, when you do that, you have to define for the outlet zeroGradient, zeroGradient or fixedValue (for p) and zeroGradient for T, for example.
But it always depends on your physics.

July 1, 2016, 05:42	Problem with BC: Setting a pressure for Inlet	#1
McCharles Member Charles K. Join Date: Feb 2016 Location: Germany Posts: 37 Rep Power: 10	Hello Foamers, I succesfully calculated a case with rhoSimplecFoam with the following BC: INLET patch : - for U : flowRateInletVelocity (massFlowRate) - for p : zeroGradient - for T : fixedValue OUTLET patch : - for U : pressureInletOutletVelocity - for p : fixedValue - for T : zeroGradient The results are looking good but as OpenFoam calculates the pressure at the Inlet, there is a small difference with my experimental results at this location. Now I want to try it the other way around by setting the pressure at the Inlet and defining a mass Flow at the Outlet. Unfortunately, with this setup, the calculation blows up after 1 iteration. These were the settings: INLET Patch: - for U : pressureInletVelocity - for p : fixedValue - for T : zeroGradient Outlet Patch : - for U : flowRateInletVelocity - for p : outletInlet (There is a recirculation in this Area of the Domain) - for T : inletOutlet I would be very thankful if someone could give me a hint on how to fix my problem. What is wrong with my BC? I'm wondering if it is actually possible to set up a case by defining an Inlet pressure. Cheers, Charles

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July 1, 2016, 07:54		#2
TobM Member Join Date: Sep 2014 Location: Germany Posts: 88 Rep Power: 12	Two thoughts: Is it important for you to define the mass flow rate at the outlet? Try it at the inlet. In most cases, you use a totalPressure BC at the inlet. Would this be an option?

July 1, 2016, 09:37		#4
TobM Member Join Date: Sep 2014 Location: Germany Posts: 88 Rep Power: 12	MassFlowRate, totalpressure and totalTemperature at inlet are common BCs. Of course, when you do that, you have to define for the outlet zeroGradient, zeroGradient or fixedValue (for p) and zeroGradient for T, for example. But it always depends on your physics.