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Setting BCs for Riverine Flows using Interfoam

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Old   June 2, 2013, 05:59
Default manning's roughness coefficient in OpenFoam
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ali naqi mohammadi
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Quote:
Originally Posted by trinath2rao View Post
Dear Foamers,

I am working on dambreak flow in an open channel. can any one help me how to specify manning's roughness coefficient in OpenFoam.

I checked manual and code, no success.

Is there anyway to specify bottom friction in OpenFoam ?

Thank You in advance.

Regards,
Trinath Rao
hi ,in the OF you should obtain roughness effect by Ks and Cs. you may find them in nut. for example:
walls
{
type nutkRoughWallFunction;
value uniform 0;
Ks uniform .0014;
Cs uniform .5;
}
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Old   April 25, 2014, 10:47
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Hey all,
I'm working at a similar problem at the moment and hope anyone could help me. I have a free surface flow channel with a narrowing. Like before I want to give the inlet velocity (here 0.5 m/s), but I need to give a predefined outlet-pressure somehow (because I need to be able to calculate for a given water elevation at the outlet).

I thought I couldn't define a pressure for the whole outlet, so I chose to define it only at the bottom of the river bed (over the last m of the channel before the outlet). The idea was to be able to give a certain hydrostatic pressure at the ground, which should define the water level.
  • Inlet: alpha = fixedValue (1), U = fixedValue (0.5 0 0), p_rgh = fixedFluxPressure (0)
  • Outlet: alpha = inletOutlet (0), U = pressureInletOutletVelocity (0 0 0), p=fixedFluxValue (0)
  • Outlet (bottom): p = phaseHydrostaticPressure;
    phaseName alpha.water;
    rho 1000;
    pRefValue 3000;
    pRefPoint (0 0 0);
    value uniform 0;
I wasn't sure how to define that, has anyone ever tried this or would do it for me? Or are there other solutions? I also get problems with alpha reflecting at the outlet sometimes...

Casefiles (currently negative x-axis, to avoid the problem of reflecting -.-):


Thanks and have a nice WE,
Benji
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Old   November 5, 2014, 07:07
Default fixed depth water at outlet
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for implementation of fixed depth at outlet, first you should divide the mesh block into two blocks: one with height of the outlet depth and the other for air.
so we will have two outlet: waterOutlet and airOutlet.
zeroGradient boundary condition for waterOutlet .
atmosphere boundary condition for airOutlet.
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Old   November 5, 2014, 08:17
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Albrecht vBoetticher
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Hi Benji,

have you tried just
outlet
{
type buoyantPressure;
value uniform 0;
}
for p_rgh ?
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Old   November 10, 2014, 05:49
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Antonio
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Hi Benji,

Have you tried Kflora suggestion. I have used in some steady open flows succesfully. I would suggest to enlarge the end of the channel to reduce influence of using a uniform 1D velocity profile.

Her suggestion is to use a fixed velocity bc of water flow rate input/ water depth aim. Being it applied to all the outlet surface (water and air)



Quote:
Originally Posted by Benji View Post
Hey all,
I'm working at a similar problem at the moment and hope anyone could help me. I have a free surface flow channel with a narrowing. Like before I want to give the inlet velocity (here 0.5 m/s), but I need to give a predefined outlet-pressure somehow (because I need to be able to calculate for a given water elevation at the outlet).

I thought I couldn't define a pressure for the whole outlet, so I chose to define it only at the bottom of the river bed (over the last m of the channel before the outlet). The idea was to be able to give a certain hydrostatic pressure at the ground, which should define the water level.
  • Inlet: alpha = fixedValue (1), U = fixedValue (0.5 0 0), p_rgh = fixedFluxPressure (0)
  • Outlet: alpha = inletOutlet (0), U = pressureInletOutletVelocity (0 0 0), p=fixedFluxValue (0)
  • Outlet (bottom): p = phaseHydrostaticPressure;
    phaseName alpha.water;
    rho 1000;
    pRefValue 3000;
    pRefPoint (0 0 0);
    value uniform 0;
I wasn't sure how to define that, has anyone ever tried this or would do it for me? Or are there other solutions? I also get problems with alpha reflecting at the outlet sometimes...

Casefiles (currently negative x-axis, to avoid the problem of reflecting -.-):


Thanks and have a nice WE,
Benji
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Old   January 11, 2016, 02:17
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Hi every one!
I have a similar problem.
I have a 3D open channel which has a curved route. I want to enter a fully developed flow in the inlet and don't know how it will be at the outlet.
can any one tell me what are the right boundary conditions for inlet, outlet and free surface? thanks a lot.
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Old   February 11, 2017, 13:50
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Quote:
Originally Posted by fatemehfarshi62 View Post
Hi every one!
I have a similar problem.
I have a 3D open channel which has a curved route. I want to enter a fully developed flow in the inlet and don't know how it will be at the outlet.
can any one tell me what are the right boundary conditions for inlet, outlet and free surface? thanks a lot.
Hi,

I am facing similar issues, I am working of flow past plate . Did you mamnge to make this work for you ?
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Old   February 12, 2017, 00:42
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Quote:
Originally Posted by Bashar View Post
Hi,

I am facing similar issues, I am working of flow past plate . Did you mamnge to make this work for you ?

Hi! for velocity, enter flowRateInletVelocity for inlet and inletOutlet for outlet.
for Pressure, zeroGradient for inlet and fixedValue for outlet.
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Old   February 12, 2017, 00:50
Default Setting BCs for Riverine Flows using Interfoam
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Quote:
Originally Posted by fatemehfarshi62 View Post
Hi! for velocity, enter flowRateInletVelocity for inlet and inletOutlet for outlet.
for Pressure, zeroGradient for inlet and fixedValue for outlet.


Thanks a lot for the info.Will be ok for you to share the case file ?
But thanks anyway,I will try your BC.I am using single inlet patch,I saw some cases where they use two separate inlet patches,one for air and the other for water. Did you use single inlet?


Thanks

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Last edited by Bashar; February 14, 2017 at 14:35.
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Old   February 12, 2017, 01:23
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Quote:
Originally Posted by Bashar View Post
Thanks a lot for the info.Will be ok for you to share the case file ?
But thanks anyway,I will try your BC.I am using single inlet patch,I saw some cases where they use two separate inlet patches,one for air and the other for water. Did you use single inlet?



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No, I just have one inlet.
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Old   February 12, 2017, 01:29
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Quote:
Originally Posted by fatemehfarshi62 View Post
No, I just have one inlet.


Thanks , I will try it .


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Old   February 14, 2017, 16:18
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Quote:
Originally Posted by fatemehfarshi62 View Post
Hi! for velocity, enter flowRateInletVelocity for inlet and inletOutlet for outlet.
for Pressure, zeroGradient for inlet and fixedValue for outlet.
Sorry to bother you again . I have another question, if I used single inlet patch for the channel, is there away to specify the speed of the air? I am currently specifying only one speed which is the water speed.So, the water and the air will have same speed, but I want to know how I can give them different speed while using one inlet patch.

Bashar
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