CFD Online Discussion Forums - Basic use of actuationDiskSource

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Basic use of actuationDiskSource

I am trying to model the effect of a helicopter in a flow with the actuator disk method. I don't have a lot of experience in this field, so my first approach is to use OpenFOAM's actuationDiskSource in a cylindrical cell set, but I don't manage to obtain the desired flow.

I created first a really basic mesh in PointWise, square domain with a cylindrical block in the center. This block is saved as cellset to use later in OpenFOAM. Free stream is in X axis, Z axis is perpendicular to the cylinder base. I want to simulate the downwash in the flow, so I expect to have in the cylynder a source of momentum added in -z direction, perpendicular to the freestream flow.

I follow the tutorial of turbineSiting, using the fvOptions file. However I can't manage to obtain the flow added by the actuator disc perpendicular to the freestream. Some times I have the flow in the x direction and other times it seems I don't even have actuator disc in the domain, no changes in the flow are present.

My understanding is that I should put diskDir (0 0 -1), to have the -z component flow. But I have no success with this approach, I have tried other components and the results are similar. Is this correct?

I also am not sure how to define the upstream point. Any point in x direction before the cylinder is valid? Or should I choose a close one and also above the cylinder in Z direction since I am looking for a vertical flow?

And finally, the area defined in the file has to match the area of the cell set? Or is just a constant for the calculation of thrust?

My fvOptions files is shown, hope you can see where my approach is failing:

Code:

/*--------------------------------*- C++ -*----------------------------------*\

| =========                 |                                                 |

| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |

|  \\    /   O peration     | Version:  4.0                                   |

|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |

|    \\/     M anipulation  |                                                 |

\*---------------------------------------------------------------------------*/

FoamFile

{

    version     2.0;

    format      ascii;

    class       dictionary;

    location    "constant";

    object      fvOptions;

}

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



disk1

{

    type            actuationDiskSource;

    active          on;



    actuationDiskSourceCoeffs

    {

        fields      (U);



        selectionMode   cellSet;

        cellSet         rotor-cells;

        diskDir         (0 0 -1);    // Orientation of the disk

        Cp              0.386;

        Ct              0.58;

        diskArea        6.283;

        upstreamPoint   (-2.5 0 0);

    }

}







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

Thanks!

I haven't manage to make any progress with my problem. Is it even possible to simulate a vertical downwash with ActuationDiskSource?

As I said, for a horizontal direction, diskDir (-1 0 0) in fvOptions, the source is detected and the increment in velocity can be seen in the region after the cylinder, in X direction. If I try vertical, diskDir (0 0 -1), nothing changes in the flow field, no momentum is added in any direction.

I have tried several positions for the upstream point, several ways to define the cellSet (with pointwise or using topoSet with the exact same steps as turbineSiting tutorial, with boxToCell or cylinderToCell and always checking with paraFoam if the cellSet is defined correctly), also OpenFOAM 4.0 and OpenFOAM 1.612 foss, several meshes and several coefficients for the disk.

I am starting to run out of options to check, does anyone have suggestions regarding this problem? Is there any similar alternative for the modelling of the downwash rotors?

Hi Alex,

Could you share your complete case files? If it is not possible, could you share your topoSet file?

Depending on your mesh resolution, topoSet is not finding the region where the disk should be, this happened to me some times...

Best Regards,
Luis

Hi,

Did you manage to solve the problem related to the upstream point? I can successfully simulate the flow for my geometry but I need to calculate the power output of the turbines I am simulating with the actuator disk. I suspect the solution has something to do with upstreamPoint but I have no idea how to use it. I am using the variable scaling method, as I want to include multiple turbines in the domain.

Kim