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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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ali naqi mohammadi
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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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