[Nick D]

Hi FOAMers!

Actuator disks add instead of reducing momentum. This is solved by changing the disk 180 degrees,but then 'diskDir' is not right and same as the "windDirection" vector, but opposite.

The library works just fine for specific directions but for others not. To be more specific, for some directions, the "diskDir" vector found in "system/fvOptions", needs an opposite sign from the "windDirection" vector found in "0/include/ABLconditions"

From 280 to 140 degrees, I get the cases working with the vector configurations, being the same between the two files, as given by the files below:

-file: "0/include/ABLconditions"
\*---------------------------------------------------------------------------*/

Uref 15.0;
Href 500.0;
windDirection (0.866025403784 0.5 0);
zDirection (0 0 1);

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

-file: "system/fvOptions"

disk1
{
type actuationDiskSource;
active on;
selectionMode cellSet;
cellSet actuationDisk1;
actuationDiskSourceCoeffs
{
fieldNames (U);
diskDir (0.866025403784 0.5 0);
Cp 0.53;
Ct 0.4;
diskArea 3019.0705401;
upstreamPoint (-612.255455478 573.888162569 326.6);
}
}

Disks_right_Diskdir| wrong results.jpg


For this direction case, the "diskDir" vector needs opposite signs when compared to the "windDirection" vector found in "0/include/ABLconditions". I do not know why this is happening

-file: "0/include/ABLconditions"
\*---------------------------------------------------------------------------*/

Uref 15.0;
Href 500.0;
windDirection (0.866025403784 0.5 0);
zDirection (0 0 1);

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

-file: "system/fvOptions"

disk1
{
type actuationDiskSource;
active on;
selectionMode cellSet;
cellSet actuationDisk1;
actuationDiskSourceCoeffs
{
fieldNames (U);
diskDir (-0.866025403784 -0.5 0);
Cp 0.53;
Ct 0.4;
diskArea 3019.0705401;
upstreamPoint (-612.255455478 573.888162569 326.6);
}
}

Disks_wrong_Diskdir| right results.jpg


As mentioned earlier, this issue appears only for specific orientations of the disks. It needs to become clear, that the "windDirection" vector produces the field right. The "diskDir" vector orientation is the one that depending on the wind direction, needs to be corrected by simply changing the signs.

To sum up, when this problem appears, by changing the "diskDir" vector to opposite signs (turning the disk orientation by 180 degrees), then the problem is solved, but this directional vector value is wrong.

I would deeply appreciate anyone's help on the issue!

Best regards,

Nick

[Nick D]

I checked all upstream points for each disk. I also tried to modify the "p1" and "p2" values defined in "topoSetDict" file, by simply considering the p2 as p1 and the p1 as p2. Did not make any difference so far. I am not expert to judge but my impression is that "diskDir" is the issue, since changing the signs only of the vector, works like a charm, although "diskDir" is wrong. Still trying to figure out....

[wyldckat]

For future reference, this is being addressed here: http://www.openfoam.org/mantisbt/view.php?id=1681

[gonzaCSC]

Hello guys,

this DiskDir issue comes from the ActuatorDisk code. Let me explain with two examples:

1)
wind direction taken from upstreamPoint is (1 0 0)
diskDir (1 0 0)

This will work fine, just like the tutorial.


2)
wind direction taken from upstreamPoint is (-1 0 0)
diskDir (-1 0 0)

It will not work. When the direction of the wind is negative, the direction of the diskDir couldnt be the same. You should change the sign:

diskDir(1 0 0)

Hope it will help you.