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wake coarsening
Dear David
I am very interested in your proposed wake coarsening function and would like to focus my follow up research on this aspect to be able to apply it to wind farm research in the future. I don’t quite understand this quote given in your PhD thesis, can I ask a few questions on this passage?
After the vortex age has reached l1, the chordwise resolution of the wake lattice is reduced by the factor f1. This is carried out by merging f1 attached trailing vortices into a new single trailing vortex. During the combination of trailing vortices, the vorticity of all combined vortices is averaged between the contributing vortex filaments (weighted by the original vortex length). For the shed vorticity all vortices but the f th 1 shed vortices are removed from the lattice. To conserve the total shed vorticity in the wake, the vorticity of the removed shed vortices is divided up over the two neighboring shed vortex elements, weighted by distance.
The l1 represents the space, which can be defined and delineated in terms of revolutions or lifetime angles, while I have some questions about the factor f2.
1.Which parameter multiplies l2? The convection of the vortex nodes? Does it represent the distance?
2.When all the shed vortices and trailing vortices enter this space, what is the distribution of these vortices, assuming that at this point there are 18 shed vortices as well as 19 trailing vortices distributed under that age angle. How do they merge? Including their vortex node positions and circulation strength .Is it also necessary to consider their stretching and changes in the radius of the vortex core?
Thank you
Roby
Hello Roby,
there are 4 wake zones in QBlade: the near wake zone, and zones 1 to 3.
The length of each zone can either be specified in terms of “rotor revolutions” or “number of timesteps”.
In the near wake zone the wake is left untreated. For each successive zone the wake is coarsened by the integer factorsf1, f2 and f3 respectively.
A factor of 2 reduces the number of trailing wake elements by a factor of 2. For example, if the previous discretization of the wake was approximately a rotor azimuthal angle of 5°, after the first coarsening the discretization would approximately be 10°. After each wake zone ends the coarsening procedure is then applied on the already coarsened wake. For example, if both f1 and f2 are set to 2, by the start of zone 2, the discretization would have expanded to approximately 20° azimuthal angle, reflecting the cumulative effect of applying the coarsening procedure after the conclusion of each wake zone.
The coarsening process follows the procedure detailed in the text that you have already cited.
BR,
David
