CFD Online Discussion Forums - Re: value of Drag force, lift force, and pressure unexpected

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- - Re: value of Drag force, lift force, and pressure unexpected (https://www.cfd-online.com/Forums/openfoam/244876-re-value-drag-force-lift-force-pressure-unexpected.html)

mehulsasvadiya1996@gmail.

September 1, 2022 11:23

Re: value of Drag force, lift force, and pressure unexpected

Hello to all

I got some different values of cl and cd snd pressure as well. My case is a 2D airfoil; the flow comes from a downward Y direction to the upward Y. U=10.5 m/s and moving wall boundary condition. this is my pimple simulation file

HTML Code:

ExecutionTime = 39151.23 s  ClockTime = 40502 s



forceCoeffs forces execute:

    Coefficients

        Cd       : -132.7221        (pressure: -133.06389        viscous: 0.34178725)

        Cs       : 1.6577795e-16        (pressure: 1.6569721e-16        viscous: 8.0738118e-20)

        Cl       : 303.84677        (pressure: 303.33214        viscous: 0.51462964)

        CmRoll       : 1.202228        (pressure: 1.2001917        viscous: 0.0020362308)

        CmPitch       : 22.873064        (pressure: 22.553154        viscous: 0.31990978)

        CmYaw       : 0.52514043        (pressure: 0.52649277        viscous: -0.0013523468)

        Cd(f)    : -65.158823

        Cd(r)    : -67.563278

        Cs(f)    : 0.52514043

        Cs(r)    : -0.52514043

        Cl(f)    : 174.79645

        Cl(r)    : 129.05032

streamLine streamLine1 write:

    seeded 0 particles

    Tracks:0

    Total samples:0

continuityError continuityError1 write:

    local = 2.0707245e-11

    global = 2.4884514e-14

    cumulative = -3.2172443e-12



    functionObjects::vorticity vorticity writing field: vorticityField

yPlus yPlus write:

    writing field yPlus

    patch airfoil y+ : min = 0.23817668, max = 154.31507, average = 52.044156

fieldAverage fieldAverage1 write:

    Calculating averages



    Writing average fields



End

Please check it and tell me where I am wrong?

night-hawk

September 2, 2022 00:37

The simple answer is your simulation is diverging. If that is not the case then you have used wrong boundary or initial conditions.

mehulsasvadiya1996@gmail.

September 3, 2022 05:21

Quote:

Originally Posted by night-hawk (Post 835137)

The simple answer is your simulation is diverging. If that is not the case then you have used wrong boundary or initial conditions.

Thanks for reply.

How can I know that my initial boundary or boundary condition is wrong?
please check my boundary file

HTML Code:

6

(

    left

    {

        type            cyclicAMI;

        inGroups        1(cyclicAMI);

        nFaces          715;

        startFace       138650;

        matchTolerance  0.0001;

        transform       unknown;

        neighbourPatch  right;

        AMIMethod       faceAreaWeightAMI;

        restartUncoveredSourceFace 1;

    }

    right

    {

        type            cyclicAMI;

        inGroups        1(cyclicAMI);

        nFaces          715;

        startFace       139365;

        matchTolerance  0.0001;

        transform       unknown;

        neighbourPatch  left;

        AMIMethod       faceAreaWeightAMI;

        restartUncoveredSourceFace 1;

    }

    inlet

    {

        type            patch;

        nFaces          80;

        startFace       140080;

    }

    outlet

    {

        type            patch;

        nFaces          80;

        startFace       140160;

    }

    airfoil

    {

        type            wall;

        inGroups        1(wall);

        nFaces          310;

        startFace       140240;

    }

    leftRight

    {

        type            empty;

        inGroups        1(empty);

        nFaces          139600;

        startFace       140550;

    }

)

Thanks

night-hawk

September 3, 2022 08:52

Can you show your model in diagram? I have just noticed that y+ value is very high (assuming you are using a low- Reynolds Turbulence Model).

mehulsasvadiya1996@gmail.

September 3, 2022 09:34

Quote:

Originally Posted by night-hawk (Post 835202)

Can you show your model in diagram? I have just noticed that y+ value is very high (assuming you are using a low- Reynolds Turbulence Model).

Thanks for reply.

Which diagram do u want to see?

night-hawk

September 3, 2022 11:33

The model you are using for simulation.

mehulsasvadiya1996@gmail.

September 3, 2022 11:35

Quote:

Originally Posted by night-hawk (Post 835209)

The model you are using for simulation.

Thanks

Can you send me your Email-ID? I will send you the whole file and you can check it.

mehulsasvadiya1996@gmail.

September 3, 2022 11:42

1 Attachment(s)

Quote:

Originally Posted by mehulsasvadiya1996@gmail. (Post 835210)

Thanks

Can you send me your Email-ID? I will send you the whole file and you can check it.

I have attached file here please check it

night-hawk

September 3, 2022 12:12

I am not sure what you trying to achieve, your Inlet has normal in x direction but it has velocity value in y direction. Are you trying to rotate airfoil to change angles of attack?

mehulsasvadiya1996@gmail.

September 3, 2022 12:14

Quote:

Originally Posted by night-hawk (Post 835212)

I am not sure what you trying to achieve, your Inlet has normal in x direction but it has velocity value in y direction. Are you trying to rotate airfoil to change angles of attack?

Thanks!!!

My inlet is IN Y-direction upward and outlet is top od Y-direction and have moving wall left and right as mentioned in blockMesh. I am not trying to change AOA.

Thanks

night-hawk

September 3, 2022 12:19

Are you using dynamic mesh in your simulation?

mehulsasvadiya1996@gmail.

September 3, 2022 12:21

Quote:

Originally Posted by night-hawk (Post 835214)

Are you using dynamic mesh in your simulation?

No, I am using cyclicAMI.

mehulsasvadiya1996@gmail.

September 4, 2022 15:35

Quote:

Originally Posted by night-hawk (Post 835214)

Are you using dynamic mesh in your simulation?

Hello Sir,

Have you checked my files? Where am I wrong?

night-hawk

September 5, 2022 02:59

One thing I noticed is nut value is 0 in initial condition. I would choose it 0.1 times of nu. Since you are not using dynamic Mesh there is no point in using AMI Interpolation. It just add additional computation cost. Last thing I will suggest is reducing max Co in controlDict to 5 from 20.

mehulsasvadiya1996@gmail.

September 5, 2022 03:16

Quote:

Originally Posted by night-hawk (Post 835278)

Thanks for reply!!!!

I have periodic boundary the left and right walls. Do u think I should use MRF Property? I still do not understand why I can not use AMI interpolation? Thanks

night-hawk

September 5, 2022 03:22

You can use periodic boundary condition for that. AMI and MRF are mainly used when mesh motion is involved.

mehulsasvadiya1996@gmail.

September 5, 2022 03:25

Quote:

Originally Posted by night-hawk (Post 835284)

You can use periodic boundary condition for that. AMI and MRF are mainly used when mesh motion is involved.

Thanks

That is why I used CyclicAMI as a periodic boundary condition.

night-hawk

September 5, 2022 03:32

I am talking about this https://www.openfoam.com/documentati...ed-cyclic.html

Here you can get more Info https://www.cfd-online.com/Forums/op...cyclicami.html

mehulsasvadiya1996@gmail.

September 5, 2022 04:01

Quote:

Originally Posted by night-hawk (Post 835287)

I am talking about this https://www.openfoam.com/documentati...ed-cyclic.html

Here you can get more Info https://www.cfd-online.com/Forums/op...cyclicami.html

Thanks

After reading this I have not found any wrong with my Boundary conditions. Have you seen anything wrong?

night-hawk

September 5, 2022 04:24

I don't understand why are using cyclic boundary condition? Your simulation involves measuring Cd and Cl on a airfoil. Anyways you probably need to edit nut initial condition and run the simulation. And also add log file of your simulation if you encounter any error it helps a lot.

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