span-wise drag/lift forces of cylinder

span-wise drag/lift forces of cylinder

SR Description:   Dear Sir/Madam,

I am trying to simulate a 3d finite immersed cylinder. I am interested the variation of drag/lift forces along the span-wise direction (the length direction) of the cylinder. The theory guide says that the force on the wall zones are calculated, thus I only get the mean drag/lift forces of the whole cylinder. Is there a way to separate the drag/lift forces along the length (z direction) direction?

ps: an experimental snap is attached.

Technical Details:

Regarding your query, I think one way to compute drag/lift is by creating custom field functions.

Create a Custom field function (CFF) for lift, with the formula

lift = pressure * Y-face area + Y-wall shear stress * face-area-magnitude.

Lift=

For drag force, I guess its simply skin_friction_coefficient*area normal to face.

Skin_friction_coefficient*x-face_area

The second approach is to write a UDF using DEFINE_ON_DEMAND macro. Loop over all the faces and get Drag and lift forces using their standard definitions.

Reply 2

The best way to do what you are requesting is to split the cylinder into strips and integrate the forces over each strip individually. This can be explicitly done at the geometry stage and meshed in strips or you can also create the strips using Iso-clip option to create a number of faces out of a single face and calculate the drag directly on those.

The last approach I mentioned by creation of clipped surfaces would require that you use a CFF to recalculate the forces (as Vivek suggested) as user defined surfaces are not by default available in the force reports panel.

The other option would be to separate the walls physically by using adaption registers to mark cells within certain ranges in the Z direction so you would have volumetric marks which would define these strips you require. The second step is then to use Mesh -> Separate -> Faces -> By Mark to separate the cylindrical wall into your strips. This would allow you to use the drag/lift reports (as would explicitly meshing the cylinder in strips).