[kanes]

Hello,

I am trying to use multiphaseEulerFoam with my case. It looks like this:


What I want:
At t = 0, this area is full of air;
Water flows into this area from the top and then flows out of this area from the bottom.

However it does not work.
Water just stopped at the top (at t = 25s), shown in the picture :


I am using the following initial conditions:
alpha.water:

dimensions      [0 0 0 0 0 0 0];

internalField   uniform 0;

boundaryField
{
    outlet
    {
      type            zeroGradient;
    }
    inlet
    {
         type             fixedValue;
         value            uniform 0.5;
    }
    walls
    {
        type            zeroGradient;
    } 
}

alpha.air:

dimensions      [0 0 0 0 0 0 0];
internalField   uniform 1;
boundaryField
{
    outlet
    {
      type            zeroGradient;
    }
    inlet
    {
        type              fixedValue;
        value             uniform 0.5;
    }
    walls
    {
        type            zeroGradient;
    }
}

U.water:

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

internalField   uniform (0 0 0);

boundaryField
{
    outlet 
    {  
         type               pressureInletOutletVelocity;
           phi                  phi.water;
          value              uniform (0 0 0);
     }
    inlet
    {
          type               flowRateInletVelocity;
           massFlowRate        constant 0.027778;
           value             uniform (0 0 0);
     }
    walls
    {
        type               noSlip;
    }
}

U.air:

dimensions      [0 1 -1 0 0 0 0];
internalField   uniform (0 0 0);
boundaryField
{
   outlet 
    {
           type               pressureInletOutletVelocity;
            phi                  phi.air;
           value               $internalField;
    }
    inlet
    {
          type                 fixedValue;
          value              uniform (0 0 0);            
    }
    walls
    {
       type               noSlip;
    }
}

p_rgh:

dimensions          [1 -1 -2 0 0 0 0];
internalField       uniform 0;
boundaryField
{
    outlet 
    {
            type             fixedValue;
           value               $internalField;
    }
    inlet 
    {
        type            fixedFluxPressure;
        value           $internalField;
    }
    walls
    {
        type            fixedFluxPressure;
        value             $internalField;
    }
}

Can someone indicate me where I am wrong?

regards,
Cheng

[saddy]

try two things,
first try to give velocity for water instead of mass flow rate,
second plz check
whether your inlet is a patch or a wall, bcz if its a wall water cannot enter
hope that helps

[kanes]

Originally Posted by saddy

try two things,
first try to give velocity for water instead of mass flow rate,
second plz check
whether your inlet is a patch or a wall, bcz if its a wall water cannot enter
hope that helps

Hey Sandy,

thank you very much!
I set the inlet as 'patch', then it works.

But now new problem is, the Phase-sum volume fraction always increased.
I also use the velocity for water (inlet)

do you have any suggestions for this?

thanks

[saddy]

i m glad i could help
now what is your error?? can u copy paste it here?
and what about mass flow rate have u tried with ur old boundary conditions??

[Swift]

Do you mean the phase sum increased above 1?
What did you set the outlet to. Is it also patch?


Sent from my EVA-L19 using CFD Online Forum mobile app

[kanes]

Originally Posted by saddy

i m glad i could help
now what is your error?? can u copy paste it here?
and what about mass flow rate have u tried with ur old boundary conditions??

Hi Sandy,

thanks.

sorry for late reply.

yes, I've tried also the mass flow rate, but after some iterations the ' Phase- sum volme fraction' incresed abouve 1.
like this:

Phase-sum volume fraction, min, max = 1 0.999983 1.18336

do you have any suggestions for the boundary conditions?

thanks

[kanes]

Originally Posted by Swift

Do you mean the phase sum increased above 1?
What did you set the outlet to. Is it also patch?


Sent from my EVA-L19 using CFD Online Forum mobile app

hey Thomas,

yes, above 1.
I have set the outlet as patch.

do you have any suggestion?

thanks

[kanes]

Originally Posted by saddy

i m glad i could help
now what is your error?? can u copy paste it here?
and what about mass flow rate have u tried with ur old boundary conditions??

Hey Sandy,
I have also tried to define the Inlet (patch) for water and air separately, as follows:


Then I also changed the alpha file like this:
alpha.air:

dimensions [0 0 0 0 0 0 0];

internalField uniform 1;

boundaryField
{
walls
{
type zeroGradient;
}

bottom
{
type zeroGradient;
}

top_water
{
type fixedValue;
value uniform 0;

}
top_air
{

type zeroGradient;
}
}

alpha.water

dimensions [0 0 0 0 0 0 0];

internalField uniform 0;

boundaryField
{
walls
{
type zeroGradient;
}

bottom
{
type zeroGradient;
}
top_water
{
type fixedValue;
value uniform 1;
}
top_air
{

type zeroGradient;
}

}

However after some time the 'Phase-sum volume fraction' still increased above 1.
I didnt figure out.

[saddy]

Originally Posted by kanes

Hey Sandy,
I have also tried to define the Inlet (patch) for water and air separately, as follows:


Then I also changed the alpha file like this:
alpha.air:


alpha.water


However after some time the 'Phase-sum volume fraction' still increased above 1.
I didnt figure out.

your alpha seems fine. i guess now problem is somewhere in p/u files
don't fix outlet pressure with internal field. use zero gradient b.c instead

[kanes]

Thanks.

the p_rgh and U.* file as follows:
p_rgh

boundaryField
{
bottom //outlet
{

type fixedValue;
value uniform 0;


}
top_air
{
type fixedFluxPressure;
value $internalField;


}
top_water
{
type fixedFluxPressure;
value $internalField;


}
walls
{
type zeroGradient;
}
}

U.air

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

internalField uniform (0 0 0);

boundaryField
{

bottom
{

type pressureInletOutletVelocity;
phi phi.air;
value $internalField;
}
walls
{
type fixedValue;
value uniform (0 0 0);
}

top_air
{
type fixedValue;
value uniform (0 0 0);

}
top_water
{

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

U.water

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

internalField uniform (0 0 0);

boundaryField
{
bottom
{

type pressureInletOutletVelocity;
phi phi.water;
value $internalField;

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

top_air
{

type pressureInletOutletVelocity;
phi phi.water;
value $internalField;

}
top_water
{
type flowRateInletVelocity;
massFlowRate constant 0.1;
value uniform (0 0 0);
// type fixedValue;
// value uniform (0 0 -0.03368);

}
}

Water should flows out from the bottom.
If I use 'zeroGradient' for the outlet pressure, then there is the problem with Continuity.

[saddy]

hey look. i can't specifically give u all b.c. what i can give u is physical setup for b.c.
your phases are flowing counter-currently right??
so 1. you have to give separate inlets and outlets..ok
2. face 1 : inlet for air, oulet for water face 2: outlet for air inlet for water
now imagine if your surrounding four patches are "walls" and both 2 faces are allowing mass to accumulate. and rate of mass inlet is greater than rate of mass leaving. where will this mass go then??
so it will push back the lighter phase more, i.e. air from inlet, some of the water will also be pushed back because we are using incompressible flow, so this is referred to as backflow, openfoam allows tis condition to be modelled using "inletoutlet" and "outletinlet" boundary condition where backflow is specified using "value"
so try using inletoutlet bc. for alpha ,and see if error comes
basically we have try to adjust b.c. u can't just setup bc in one go. it takes time
keep trying you will eventually get it
good luck

[kanes]

Hey Sandy,

thanks a lot!