[MechEng86]

Hi Everyone,

I’m new to CFD and trying to analyse a vertical axis wind turbine, whereby the blades can be pitched independently of rotor rotation, about the 25% blade chord position. I have setup the geometry similar to that in the attached JPEG, only one blade has been shown, but I am planning on analysing 2 and 4 blade configurations.

From reading the Fluent manual, as the blade region angular velocity is not going to be constant with rotor rotation, this has led me to believe that I need to write my own UDF. I have defined two possible options I think, and was wondering if anyone would be able to give me some advice on their applicability and the best way to set this problem up. I wasn’t sure which would be the most applicable. It will be easier for me to calculate displacement/rotation of the blade as opposed to velocities.

Firstly DEFINE_CG_MOTION. My understanding is that for this case the angular velocity of the rotating region is calculated, and the region in question then rotates about its COG postion. In this problem the COG position of the yellow blade region is at the 25% blade chord position which is the blade pitch axis. But as the rotor is rotating the COG position of the yellow region is moving, can this be specified in DEFINE_CG_MOTION?

Secondly DEFINE_GRID_MOTION, what I would like to be able to do ultimately is link the blade and rotor rotation, so say that for every 1 degree of rotor rotation I could then calculate the corresponding rotation of the blade region. I was planning on using rigid body motion for the rotor and blade regions, but my understanding is that the DEFINE_GRID_MOTION UDF is only for deforming meshes. My problem isn’t a true deforming mesh problem; I would like to be able to rotate the complete mesh within the yellow blade region as one body relative to the rotor region, at their interface, by specifying the appropriate equations. Is this possible with DEFINE_GRID_MOTION?

Also would I have to specify a separate UDF loop for each blade, so have 4 in the case of 4 blades?

Any advice would be much appreciated