[Jeggi]

Hi All,

I am trying to simulate the transient tidal flow in a strait using a single-phase model and boundary conditions that vary in time and space. The boundary conditions are received from an ocean model. The setup has already been done in Fluent (see https://www.youtube.com/watch?v=UanYru7E0gI&t=13s), but because our research license has expired, we would like to attempt to run the simulation in OpenFOAM.

The strait is 1.2 km wide and about 8 km long. It is tidally driven, meaning that there is both inflow and outflow at both ends. The Fluent setup used a velocity inlet with a specified profile at each end and an outflow boundary condition placed in the middle of the domain (at “Leynar” in the animation) to ensure mass balance. The outflow boundary condition is required because the ocean model can give a few percent difference in volumetric flow rate due to tidal rise.

The strait inlet/outlets are called profile1 and profile.

I would expect that using a timeVaryingMappedFixedValue for U and a zeroGradient for p would be equivalent to Fluent velocity inlet condition. The outflow is modeled as zeroGradient for U and fixedPressure of 0 for p.

The simulation does run, but there are clear issues of unphysical velocities near the profile that serves as the outlet boundary condition. See https://www.youtube.com/watch?v=hhJ-m-a27VI and the attached image.

When I plot the boundary patches of my inlets and outlets, the velocity profiles seem to be correctly implemented (see profile1_u.png). However, when I plot the pressure on the boundary with the velocity condition that is currently functioning as an outlet, I observe clear indications of issues (see profile1_p.png). In contrast, if I plot the pressure patch of the boundary that is currently functioning as an inlet, the pressure field appears correct.

Does anyone have suggestions on how to mitigate this issue? I've tried using different types of meshes (with and without snapping), lowering the time step and changing schemes, without any success.
The case can be downloaded at https://rao.fo/files/case02_newk_cfdonline.zip .

p

dimensions      [0 2 -2 0 0 0 0]; 

internalField   uniform 0;

boundaryField
{
	"(profile1|profile4)"
	{
        type            zeroGradient;
	}
	
	"(profile1_lid|profile4_lid)"
	{
        type            zeroGradient;
	}		
    overflow
    {
        type            fixedValue;
        value           uniform 0;
    }  
    "(frontAndBack|lowerWall|upperWall)"
    {
        type            zeroGradient;
    }
    bath
    {
        type            zeroGradient;
    }
}

U

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

//internalField   uniform (0.0 0 0);

internalField   uniform (0.0 0.0 0.0);

boundaryField
{
    profile1
    {
	type            timeVaryingMappedFixedValue;
        offset          (0 0 0);
        setAverage      off;
	mapMethod 	planar; //nearest; //planar is default
    }
    profile4
    {
	type            timeVaryingMappedFixedValue;
        offset          (0 0 0);
        setAverage      off;
	mapMethod 	planar; 
		
    }   
    overflow
    {
	type zeroGradient;
    }
    "(frontAndBack|lowerWall|upperWall)"
    {
        type            slip ;
    }
    bath
    {
        type            slip;
    }
}

k

dimensions      [0 2 -2 0 0 0 0];

internalField   uniform 7.526400000000001e-06;

boundaryField
{
	"(profile1|profile4|profile1_lid|profile4_lid)"
	{
		type            turbulentIntensityKineticEnergyInlet;
		intensity       0.05; // Adjust based on turbulence intensity (e.g., 5%)
		value           $internalField;
	}
    overflow
    {
        type            inletOutlet;
        inletValue      $internalField;
        value           $internalField;
    }
    "(frontAndBack|lowerWall)"
    {
        type            zeroGradient;
    }
    "(bath|upperWall)"
    {
        type	kqRWallFunction; 
         value	uniform $internalField; 
    }
}

nut

dimensions      [0 2 -1 0 0 0 0];
// turbulent viscosity
internalField   uniform 0.0039970162311404244;//5.59e-5;

boundaryField
{
	"(overflow|frontAndBack|lowerWall)"
    {
		type            zeroGradient; 
    }

	"(profile1|profile4)"
    {

		type            calculated;
		value           uniform 0;
    }
	"(profile1_lid|profile4_lid)"
	{
		type            inletOutlet;
		inletValue      $internalField;
		value           $internalField; // Placeholder
	}
    "(bath|upperWall)"
    {
        type            nutUWallFunction;
        value           $internalField;
    }
}

omega

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

internalField   uniform 0.005;//0.0194;//calculated //0.00011846205005452487;

boundaryField
{  
    "(profile1|profile4)"
    {
        type            turbulentMixingLengthDissipationRateInlet;
        mixingLength    0.098; //d_discharge*0.07
        value           $internalField; 
    }
    overflow
    {
        type            zeroGradient;
    }
    "(frontAndBack|lowerWall)"
    {
        type            zeroGradient;
    }
    "(bath|upperWall)"
    {
        type            omegaWallFunction;
        value           uniform 0.1;
    }	
}