Hi there,
does anyone know in detail which forces the yaw torque (Mz Tower Top) depend on? It’s certainly clear that the rotor diameter is a crucial factor and the wind class of the turbine and so on. But I am more interested in the origin of a swinging motion which can lead to damages of the yaw drive on the long run.
Thanks a lot in advanced.
Felix
What kind of turbine are you talking about? How many blades? If two, does it teeter? If it teeters, does it have delta-3?
sorry for leaving out those informations: I am talking about a three bladed turbine!
Felix,
It’s actually quite complicated. Yaw errors and wind shear can cause a once-per-revolution (1P) oscillation in yaw moments when it’s operating. Imbalances in the pitch, mass, or aerodynamics can have an effect.
Are you referring to real-life experiences, or what you see in simulations? If it’s test data, you might want to try to model the turbine to reproduce the behavior in simulations.
These are just general suggestions. If you would be very explicit about the problem, we might be able to help you more.
Marshall
Hey Marshall,
well, my task is to rethink the dimensioning and construction of the yaw system for a 900kW and a 2.5 MW Turbine. Therefore I would like to understand the details of the loads on the system as good as possible. It seems to be commen to work with LDDs to calculate the lifetime of the drives and the bearings, but those LDDs neglect the chronology of the load cases.
I would like to know what’s really going on up there and what are the major factors influencing the yaw momentum. I think I am more interested in the aerodynamic forces which lead to yaw loads because the mass imbalances in the rotor are a realtivly simple part of the yaw behavior (right?).
In the report of A.C. Hansen (1992) about yaw dynamics I found some explainations, but Hansen only considered turbines with two blades and teetering. I do not know to what extend these results are suitable for a three bladed turbine too…?
so long,
Felix
Felix,
I’m no expert in gears, so others may be better suited to answer. However, my guess is that a yaw drive is fundamentally different than the gears in a gear box where the shaft turns most of the time. A yaw drive is generally stopped and must just resist the yaw moment. For this reason, I suspect the Load Duration Distribution method of analysis is not appropriate. I would be inclined to do a rainflow analysis for the yaw drive. You should run an entire loads suite (see IEC Standard 61400-x, where “x” is 1:large turbines, 2-small turbines, 3-offshore turbines) and do a fatigue analysis of the tower-top forces and moments. Our MCrunch and MLife (coming soon) postprocessors can do the fatigue analysis you would need. The analysis follows the method specified in IEC 61400-1, Ed. 3, Annex G.
Marshall
Hey,
I finally found something which that explains roughly the behaviour and characteristic of the yaw momentum:
"…The pert of the rotor that is closer to the wind becomes subject to a larger bending torque than ther rest of the rotor. This means that the rotor has a propenstiy to automatically yaw against the wind and this applies to either upwind or downwind machine designs. The rotor baldes under yaw error would be bending back and forth in a flap-wise fashion for each turn of the rotor. Running a wind turbine with a yaw error subjects it to a large fatigue load that could lead to its eventual fatigue failure… "
in
netfiles.uiuc.edu/mragheb/www/N … rbines.pdf
Thanks again for helping me thinking about anyway!
Regards
Felix