# Setting BCs for Riverine Flows using Interfoam

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June 2, 2013, 05:59
manning's roughness coefficient in OpenFoam
#21
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Quote:
 Originally Posted by trinath2rao 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;
}

 April 25, 2014, 10:47 #22 New Member   Join Date: Apr 2014 Posts: 20 Rep Power: 4 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

 November 5, 2014, 07:07 fixed depth water at outlet #23 New Member   ali naqi mohammadi Join Date: Dec 2012 Posts: 6 Rep Power: 5 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.

 November 5, 2014, 08:17 #24 Senior Member   Albrecht vBoetticher Join Date: Aug 2010 Location: Zürich, Swizerland Posts: 212 Rep Power: 9 Hi Benji, have you tried just outlet { type buoyantPressure; value uniform 0; } for p_rgh ?

November 10, 2014, 05:49
#25
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Antonio
Join Date: Jan 2013
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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 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

 January 11, 2016, 02:17 #26 Member   Fatemeh Join Date: Dec 2015 Location: Isfahan,Iran Posts: 36 Rep Power: 2 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.

 Tags interfoam, openfoam, river, vof

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