[kmallick]

I have been struggling with a 3D model for vertical wind turbine (VAWT). I thought it was high time I seek help from you all.

To the best of my knowledge, I have successfully meshed a section of a twisted savonius wind turbine blade of diameter D, placed inside a rotating cylindrical domain (rotor) that sits inside a 19D x 14D x14D cuboid domain (stator). Please see pictures below. The rotor and stator are connected by cyclic AMI. I created the stl surfaces and domains in Salome, meshed the rotor and stator separately and merged them using mergeMesh.







My model consists of a twisted surface for the wind turbine blades. Below is the section of refinementSurfaces in my sHM that helped create the baffles. Snappyhexmesh seems to have meshed the rotor correctly, snapped to the surfaces and created two separate surfaces as part of the baffle definition: blades and blades_slave.

    refinementSurfaces
    {
        rotor
        {
            // Surface-wise min and max refinement level
            level (0 0);

                 faceZone AMI1;
                 faceType boundary;           
                 patchInfo { type patch; } 

        }

        blades
        {
                 level (4 4);
                 faceZone blades;
                 faceType baffle;
         }

     }

I have accordingly defined boundary conditions separately on blades and blades_slave. Like so for U:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  dev                                   |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       polyBoundaryMesh;
    location    "constant/polyMesh";
    object      boundary;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

9
(
    AMI1
    {
        type            cyclicAMI;
        inGroups        1(cyclicAMI);
        nFaces          22800;
        startFace       4917772;
        transform       noOrdering;
        neighbourPatch  AMI2;
    }
    blades
    {
        type            wall;
        inGroups        1(wall);
        nFaces          130601;
        startFace       4940572;
    }
    blades_slave
    {
        type            wall;
        inGroups        1(wall);
        nFaces          130601;
        startFace       5071173;
    }
    bot
    {
        type            patch;
        nFaces          2640;
        startFace       5201774;
    }
    inlet
    {
        type            patch;
        nFaces          1936;
        startFace       5204414;
    }
    outlet
    {
        type            patch;
        nFaces          1936;
        startFace       5206350;
    }
    sides
    {
        type            patch;
        nFaces          5280;
        startFace       5208286;
    }
    top
    {
        type            patch;
        nFaces          2640;
        startFace       5213566;
    }
    AMI2
    {
        type            cyclicAMI;
        inGroups        1(cyclicAMI);
        nFaces          17628;
        startFace       5216206;
        transform       noOrdering;
        neighbourPatch  AMI1;
    }
)

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

I have checked in paraview and the normal glyphs of blades are are distinct from blades_slave.

I plan to run my simulation for different rotational speeds using pimpleDyMFoam. I have also requested a force calculation in Controldict like this:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  dev                                   |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/

forces
{
    type          forces;

    libs          ("libforces.so");

     writeControl  timeStep;
     timeInterval  1;

    log           yes;

    patches       (blades blades_slave);
    rho           rhoInf;     // Indicates incompressible
    log           true;
    rhoInf        1;          // Redundant for incompressible

    CofR          (0 0 0);    // Rotation around centre line of propeller

}


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

The problem I am having is with the computed Torque around the VAWT axis of rotation which is (0. 0. 0.) with normal of (0 0 1.). When I perform a simpleFoam run I get a positive torque.





However when I run pimpleDyMFoam, my computed torque (Mz) comes out negative even after several (3-4) 360 rotations of the turbine for positive omega around the z axis.



I am wondering if I have set up something wrong in defining the turbine blades as baffles. Any advice or suggestion would be highly appreciated.

I am using Openfoam-dev and a k-omega SST turbulence model.

[kmallick]

Can someone please advice on why I am getting negative moment (Mz) in my 3D model of a vertical axis wind turbine being rotated positively around the z axis?