[Pamela93]

Hello everyone,

I am trying to simulate a 3D model of a gauge station of 30 m length in a River for my master thesis in OpenFOAM. I already have created a model and I have used the solver interFoam, so now I am checking the results. For the inlet path, the graph Flow over time represents a constant Flow equal to 20.6 m3/s, which is the selected inlet value. However, checking the outlet results, the graph Flow over time shows that the flow is increasing over time and after 35 seconds of running the simulation, the flow is 80 [m3/s].
I would like to know if there is a boundary condition that allows a continuous flow flowing out of the volume to represent the real condition of a river. Furthermore, I am attaching the U file with my boundary conditions if someone would like to check it.

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  3.0.x                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volVectorField;
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 1 -1 0 0 0 0];

internalField   uniform (1 0 0);

boundaryField
{
    inlet
    {
	
        type variableHeightFlowRateInletVelocity;
		flowRate 20.6; //(m3/s)
		alpha alpha.water;
		value uniform (0 0 0);
		
		//type            variableHeightFlowRate;
        //lowerBound      0.0;
        //upperBound      0.9;
        //value           uniform 0;
   
        //type            flowRateInletVelocity;
        //volumetricFlowRate constant (10 0 0);
    }

    Flume
    {
        type            fixedValue;
        value           uniform (0 0 0);
    }

    atmosphere
    {
        type            pressureInletOutletVelocity;
        value           uniform (0 0 0);
    }

    outlet
    {
        type            zeroGradient;//inletOutlet
        //inletValue      uniform (0 0 0);
       //value           $internalField;
    }
    
}


// ************************************************************************* //

Any help and feedback are highly appreciated.