[deniggo]

Hi,
I'm working on open channel flow using interFoam. A case with fixedValue-BC for U at the inlet and p_rgh fixedValue-BC at outlet is working properly (zeroGradient BC at outlet for U and inlet for p_rgh).

But is it possible to implement a pressure drop by specifying inlet AND outlet pressure fixedValue-BC (channel slope), without a fixedValue-BC for U? Thus, U should be developed corresponding to the pressure gradient.

I tried zeroGradient and pressureInletOutletVelocity for U-inlet and outlet, but the runs failed. Which BC for U would be appropriate for thise case?

Thanks for your help,

Nico

[santiagomarquezd]

What about totalPressure for p_rgh and zeroGradient for U and alpha1 at inlet?

Regards.

[deniggo]

Hi, thanks for your answer,
I tried also totalPressure for inlet and outlet of p_rgh with no success. totalPressure is also set for the top of the channel = atmosphere.
For alpha1, I forgot to mention, I use groovyBC at inlet for time varying waterlevel.
Maybe that's the problem?

Regards.

[bmandt]

Hi,

I have the same problem trying to calc a flooding inside a ship, only with pressure given at the inlet side.

In a personal discussion at another forum, I received this answer (the discussion was in german, I try to translate it):

"
Hydrostatic pressure boundary condition calculated as
pRefValue + rho*g.(x - pRefPoint)
where rho is provided and assumed uniform.
"
for the inlet pressure: "uniformDensityHydrostaticPressure"
the velocity at the inlet: "pressureInletUniformVelocity"
water at the inlet: alpha/gamma = fixedValue; value uniform 1;
at the outlet "zeroGradient"for using Piso


unfortunately the author mentioned piso, not interfoam, but it may be, and I hope this, this information helps you. I was not able to set up an interfoam case with this information, the reason may be, that I am a very beginner at openfoam and cfd...


I hope you will give feedback.


Best regards


Benjamin

[bongbongxanh]

i suggest convert the pressure drop at the boundary condition into a pressure source, i.e. a constant gradient of pressure in the desired flow direction and add it to momentum equation in the solver. the velocity at the boundary can be set at zeroGradient or inletOutlet, the velocity itselft will then be driven by the pressure source and develop over the length of the channel.
Hope this idea can help.

[nimasam]

look into channelFoam, you can download channelInterFoam here, but i cant promise its totally true

http://www.4shared.com/file/75DpcP1g...InterFoam.html

[Andrea_85]

Hi Nico,
Have you found a solution? Have you tried channelFoam? I need to specify a pressure gradient between the inlet and the outlet of my domain and i would like that the flow was driven by this gradient.

Best

andrea

[nimasam]

use a fan boundary condition between outlet and inlet so the pressure gradient* channel length will be the value of pressure jump

[Andrea_85]

Hi nima and thanks for reply.
I never used fan BC, can you be a bit more specific about how to use them for my case? or can you direct me to some reference or tutorial?

thanks again

andrea

[deniggo]

Hi nimasam,
thanks for your help.
I tried to use fan BC. But I use groovyBC for defining the water level at the inlet. Therefore, cyclic fan BC does not work, because "inout" (cyclic patch of inlet & outlet) can not be defined by groovyBC?!

Nico

[nimasam]

use the funkySetFields to initiate the level of the water at time zero!

[deniggo]

ok! defining water level at time 0 by using setFields works. water level stays constant through the simulation.
thank you very much!

[Andrea_85]

Hi again,
I understand how to define a "inout" cyclic patch between inlet and outlet. Now my question is which is the correct boundary condition for alpha1 in "inout"?
i have

0/U
inout
{
type cyclic;
value uniform (0 0 0);
}

0/p_rgh
inout
{
type fan;
patchType cyclic;
f List<scalar> 1(1000);
value uniform 0;
}

0/alpha1
inout ??

Can i use the inletOutlet patch? I would like to have fixedValue at the inlet (uniform 1) and something like zeroGradient or inletOutlet at the outlet.

best

andrea

[nimasam]

no you can't , when you use the class cyclic, you can only use cyclic boundary condition or its sub derived class like fan
but the main question is that how ur alpha treats? is it cyclic or not? if it is not cyclic why you are going to use cyclic BC for ur simulation?

[Andrea_85]

Hi nima,
honestly i'm trying different types of boundary condition to see what is the best choice to reproduce an experiment. In the experiment the flow is driven by a pressure difference between inlet and outlet and I'm loking for something similar in my simulation (at least i would like to not specify the pressure at outlet, because i'm interesting in what happens at the breakthrough and i think fixed pressure BC affects the results). Probably you are right and my alpha1 is not cyclic because i want only phase1 which enters at the inlet and not a mix of the two (which is what flows out at the outlet). the problem remains!
if you have other ideas, of course are welcome.

best

andrea