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-   -   inlet pressure is higher than outlet pressure for fan (http://www.cfd-online.com/Forums/openfoam-pre-processing/109308-inlet-pressure-higher-than-outlet-pressure-fan.html)

sivakumar November 14, 2012 13:22

inlet pressure is higher than outlet pressure for fan
 
2 Attachment(s)
Dear Foamers,
I am running simulation using MRFSimpleFoam solver, the simulation has been done. But now i am comparing the results with experimental result.

the simulation result shows that inlet pressure is higher than outlet pressure.
I am not able to figure out the mistake in my case.
I have attached the U and P file for your consideration, please have a look and help to get it solved.

Thanks for your time and help,
Sivakumar

maddalena November 16, 2012 11:15

Hello,
some observations:
1) before asking help, this is a must-read thread: http://www.cfd-online.com/Forums/ope...-get-help.html
2) your solver is incompressible, thus a uniform 0 value should be used. Relative pressure matters.
3) Is your U defined in agreement with the coordinate system? i.e. should the flow go in positive X direction?

mad

sivakumar November 16, 2012 12:36

3 Attachment(s)
Hi Maddalena,
Thanks for the link, I am using MRFSimpleFoam,
Its a passage of axial flow fan,
I have defined velocity in x direction (i am not sure about this condition , how good it is)
I hope the defined pressure is fine. other boundary conditions are good I think.

the convergence not going beyond 0.001.
I have attached the figure, please have a look.
I have tried different schemes still the residual plot is same.
I have attached P and U, please have a look.

if you dont mind please give me you email id I will send my case for your consideration.


Thank you for your help and time,
Sivakumar

dogan May 17, 2013 12:14

hi,
i have the same problem. I am running a centrifugal pump simulation with MRFSimpleFoam. i checked my BC's, but i couldn't find the problem. it supposed to be low pressure in the inlet (suction), and high pressure in the outlet, but the results are showing the opposite.


here is the U:


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

internalField uniform (0 0 1.485);

boundaryField
{
Wall_0
{
type fixedValue;
value uniform (0 0 0);
}

Dummy_4
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Inlet_7
{
type fixedValue;
value uniform (0 0 1.485);
}
Wall_8
{
type fixedValue;
value uniform (0 0 0);
}
Dummy_10
{
type cyclicGgi;
value $internalField;
}
Dummy_11
{
type cyclicGgi;
value $internalField;
}
Dummy_12
{
type cyclicGgi;
value $internalField;
}
Dummy_13
{
type cyclicGgi;
value $internalField;
}
Dummy_14
{
type cyclicGgi;
value $internalField;
}
Dummy_15
{
type cyclicGgi;
value $internalField;
}
Dummy_16
{
type cyclicGgi;
value $internalField;
}
Dummy_17
{
type cyclicGgi;
value $internalField;
}
Dummy_18
{
type cyclicGgi;
value $internalField;
}
Dummy_19
{
type cyclicGgi;
value $internalField;
}
Dummy_20
{
type cyclicGgi;
value $internalField;
}
Dummy_21
{
type cyclicGgi;
value $internalField;
}
Dummy_24
{
type cyclicGgi;
value $internalField;
}
Dummy_25
{
type cyclicGgi;
value $internalField;
}
Dummy_26
{
type cyclicGgi;
value $internalField;
}
Dummy_27
{
type cyclicGgi;
value $internalField;
}
Wall_30
{
type fixedValue;
value uniform (0 0 0);
}
Inlet_31
{
type fixedValue;
value uniform (0 0 1.485);
}
Wall_32
{
type fixedValue;
value uniform (0 0 0);
}
Dummy_38
{
type cyclicGgi;
value $internalField;
}
Wall_39
{
type fixedValue;
value uniform (0 0 0);
}
Wall_48
{
type fixedValue;
value uniform (0 0 0);
}
Outlet_61
{
type zeroGradient;

}
Dummy_GGI_1
{
type cyclicGgi;
value $internalField;
}
Dummy_GGI_2
{
type cyclicGgi;
value $internalField;
}
Interface_22_23
{
type cyclicGgi;
value $internalField;
}
Interface_28_29
{
type cyclicGgi;
value $internalField;
}
Interface_36_37
{
type cyclicGgi;
value $internalField;
}
Interface_40_41
{
type cyclicGgi;
value $internalField;
}
Dummy_2_6_9
{
type cyclicGgi;
value $internalField;
}
Dummy_33_34_35
{
type cyclicGgi;
value $internalField;
}



and the p:


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

internalField uniform 0;

boundaryField
{
Wall_0
{
type zeroGradient;

}

Dummy_4
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Dummy_10
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Dummy_11
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Dummy_12
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Dummy_13
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Dummy_14
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Dummy_15
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Dummy_16
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Dummy_17
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Dummy_18
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Dummy_19
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Dummy_20
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Dummy_21
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Dummy_24
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Dummy_25
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Dummy_26
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Dummy_27
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Wall_30
{
type zeroGradient;

}

Inlet_31
{
type zeroGradient;

}

Wall_32
{
type zeroGradient;

}

Dummy_38
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Wall_39
{
type zeroGradient;

}

Wall_48
{
type zeroGradient;

}

Outlet_61
{
type fixedValue;
value $internalField;
}

Dummy_GGI_1
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Dummy_GGI_2
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Interface_22_23
{
type cyclicGgi;
value $internalField;
}

Interface_28_29
{
type cyclicGgi;
value $internalField;
}

Interface_36_37
{
type cyclicGgi;
value $internalField;
}

Interface_40_41
{
type cyclicGgi;
value $internalField;
}

Dummy_2_6_9
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Dummy_33_34_35
{
type cyclicGgi;
//inletValue $internalField;
value $internalField;
}

Inlet_7
{
type zeroGradient;

}

Wall_8
{
type zeroGradient;
//value $internalField
}



van you see what the problem is?

nash December 9, 2013 06:55

1 Attachment(s)
Hi everyone,

i experience the same thing when i try to simulate the centrifugal fan.
here is my BC for p and U

U;

Code:

[internalField  uniform (0 0 0);

boundaryField
{

  "rotor.*"
    {
      type            fixedValue;
      value          uniform (0 0 0);
    }
  "gehaeuse.*"
    {
      type            fixedValue;
      value        uniform (0 0 0) ;
    }

  ebene
    {
      type            fixedValue;
      value          uniform (0 0 0);
    }
  outlet
    {
      type            inletOutlet;
      inletValue      uniform (0 0 0);
      value          uniform (0 0 0);
    }
     
  inlet
    {
      type            flowRateInletVelocity;
      volumetricFlowRate $flowRate;
      value          uniform $inletFlow;
    }

  rohr
    {
      type            fixedValue;
      value          uniform (0 0 0);
    }
"interface.*"
    {
      type            cyclicAMI;
      value          $internalField;
    }

}

p;
Code:

boundaryField
{

  "rotor.*"
    {
      type            zeroGradient;
   
    }
 "gehaeuse.*"
    {
      type            zeroGradient;
     
    }

  ebene
    {
      type            zeroGradient;
   
    }
  inlet
    {
      type zeroGradient;
      value    uniform 0;
    }
  outlet
    {
      type fixedMean;
    meanValue 0;
    value uniform 0;
 }
  rohr
    {
      type            zeroGradient;
     
    }
 "interface.*"
    {
      type            cyclicAMI;
      value          $internalField;
    }

}

the flow direction is okay from inlet to outlet and the rotation in the mrf is right as well.
the only thing that seems not right is the pressure in inlet is higher than that of outlet.

anyone can help me?

thank you.

regards,
nash

sivakumar December 9, 2013 09:30

Hi There,
Check your stagger angle, how is your torque, is it fine?
if you get less pressure raise and more torque, then there could be a problem with root stagger angle.

Thanks,
Sivakumar

nash December 9, 2013 09:35

Quote:

Originally Posted by sivakumar (Post 465488)
Hi There,
Check your stagger angle, how is your torque, is it fine?
if you get less pressure raise and more torque, then there could be a problem with root stagger angle.

Thanks,
Sivakumar

im using OF 2.2.0

how can i check the stagger angle as well as torque?

thank you for your help sivakumar

regards,
nash


-btw did you managed to solve the problem of having the higher pressure inlet than that of outlet?

sivakumar December 9, 2013 09:50

root stagger angle, you need to check your design properties.
to check the torque, copy and paste the function in your controlDict file

functions
(
forces
{
type forces;
functionObjectLibs ("libforces.so");
outputControl timeStep;
outputInterval 10;
patches (fan);
// pname p;
// Uname U;
rhoName rhoInf;
log true;
rhoInf 1.20; // density of the fluid
CofR (0 0 0);
}

run the simulation again, then check the torque.

Thanks,
Sivakumar

nash December 9, 2013 10:09

after running the simulation i got this for the forces output

Code:

forces output:
    forces(pressure,viscous)((-0.00468209 -0.00186217 -0.00295491),(0.00320589 -0.00866709 -0.00189832))
    moment(pressure,viscous)((4.12521e-06 -1.51542e-05 -0.000171072),(4.11675e-05 2.99142e-05 0.000155277))

how can i analyse them?

about the stagger angle, i think it is ok since it was constructed from the real fan.

sivakumar December 9, 2013 10:26

Check with your experimental torque, I think your torque is zero.
so you need to check your angle.

nash December 9, 2013 10:42

i will check it then.

but in your case, what is the problem that you were facing and how you overcome it?

thanks,
nash

nash December 9, 2013 13:56

i dont have the data
-nash-

nash December 11, 2013 09:57

i check my boundary conditions and compare them with the test case from the single channel pump with the mrf.
i cant see any much difference between them. however the pressure i get at inlet is lower than that of at outlet. i have check my mrf dict (fvOption) everything is fine.
so anyone can help me how to solve this ?

channelPumpCase
Code:

FoamFile
{
    version 2.0;
    format binary;

    root "/wrk6/mauvinen/wrkOpenFOAM/caseStorage";
    case "tubePumpWF";
    instance "0";
    local "";

    class volVectorField;
    object U;
}

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

dimensions      [0 1 -1 0 0 0 0];

internalField  uniform (0 0 0);

boundaryField
{
    impellerWall
    {
        type            fixedValue;
        value          uniform (0 0 0);
    }
    inletDuct
    {
        type            fixedValue;
        value          uniform (0 0 0);
    }
    inlet
    {
        type            fixedValue;
        value          uniform (0 0 3.407);
    }
    impellerRim
    {
        type            fixedValue;
        value          uniform (0 0 0);
    }
    voluteWall
    {
        type            fixedValue;
        value          uniform (0 0 0);
    }
    outletDuct
    {
        type            fixedValue;
        value          uniform (0 0 0);
    }
    outlet
    {
        type            zeroGradient;
    }

  insideGGI
  {
        type        ggi;
  }
  outsideGGI
  {
        type        ggi;
  }
}

Code:

FoamFile
{
    version 2.0;
    format binary;

    root "/wrk6/mauvinen/wrkOpenFOAM/caseStorage";
    case "tubePumpWF";
    instance "0";
    local "";

    class volScalarField;
    object p;
}

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

dimensions      [0 2 -2 0 0 0 0];

internalField  uniform 500;

boundaryField
{
    impellerWall
    {
        type            zeroGradient;
    }
    inletDuct
    {
        type            zeroGradient;
    }
    inlet
    {
        type            zeroGradient;
    }
    impellerRim
    {
        type            zeroGradient;
    }
    voluteWall
    {
        type            zeroGradient;
    }
    outletDuct
    {
        type            zeroGradient;
    }
    outlet
    {
        type            fixedValue;
        value          uniform 500;
    }

  insideGGI
  {
        type        ggi;
  }
  outsideGGI
  {
        type        ggi;
  }

}

MyCase

Code:

FoamFile
{
    version    2.0;
    format      ascii;
    class      volScalarField;
    location    "0";
    object      p;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 2 -2 0 0 0 0];
#include "include/initialConditions_q10_p132_5"
internalField  uniform 0 ;

boundaryField
{

  "rotor.*"
    {
      type            zeroGradient;
   
    }
 "gehaeuse.*"
    {
      type            zeroGradient;
     
    }

  ebene
    {
      type            zeroGradient;
   
    }
  inlet
    {
      type zeroGradient;
      value    uniform 0;
    }
  outlet
    {
      type fixedMean;
    meanValue 0;
    value uniform 0;
 }
  rohr
    {
      type            zeroGradient;
     
    }
 "interface.*"
    {
      type            cyclicAMI;
      value          $internalField;
    }

}

Code:

FoamFile
{
    version    2.0;
    format      ascii;
    class      volVectorField;
    location    "0";
    object      U;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 1 -1 0 0 0 0];

#include "include/initialConditions_q10_p132_5"


internalField  uniform (0 0 0);

boundaryField
{

  "rotor.*"
    {
      type            fixedValue;
      value          uniform (0 0 0);
    }
  "gehaeuse.*"
    {
      type            fixedValue;
      value        uniform (0 0 0) ;
    }

  ebene
    {
      type            fixedValue;
      value          uniform (0 0 0);
    }
  outlet
    {
      type            inletOutlet;
      inletValue      uniform (0 0 0);
      value          uniform (0 0 0);
    }
     
  inlet
    {
      type            flowRateInletVelocity;
      volumetricFlowRate $flowRate;
      value          uniform $inletFlow;
    }

  rohr
    {
      type            fixedValue;
      value          uniform (0 0 0);
    }
"interface.*"
    {
      type            cyclicAMI;
      value          $internalField;
    }

}


nash December 12, 2013 17:22

hi everyone its me again..
i know no one is replying to my question, but i will keep posting :)

so far i have done a simulation of radial fan with elongated cylinder lenght about 10 times of of the inlet diameter. The outlet is a semi hemisphere. But then i got pressure inlet higher than that of at outlet. So this is totally wrong. Fan should increase the pressure outlet.

So my next step is to change the inlet as semi hemsphere and for the outlet i just extend the end of the housing in about 10 times of the outlet (housing) diameter.
i will inform you guys about the result tomorrow. 2 variations of BC i will implement are assigning pressure difference between inlet and outlet, and assigning flowrate (maybe at outlet)

if anyone has suggestion, please feel free to post here. I hope i can get a good result and share this with others and helping each other.

thank you
regards,
nash

nash December 16, 2013 10:58

just a litte mistake from the mrf Definition in fvOption

in nonRotatingPatches

i just actually need to add AMI patches. Any rotating walls should not be added in nonRotatingPatches.

my inlet pressure is now lower than that of outlet.

hope this would help other fan simulator :)


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