Abstract
A dynamic stall model for tower shadow effects is developed for downwind turbines. Although Munduate’s model shows good agreement with a 1.0 m wind tunnel test model, two problems exist: (1) it does not express load increase before the entrance of the tower wake, and (2) it uses the empirical tower wake model to determine the wind speed profile behind the tower. The present research solves these problems by combining Moriarty’s tower wake model and the entrance condition of the tower wake. Moriarty’s model does not require any empirical parameter other than tower drag coefficient and it expresses positive wind speed around the tower also. Positive wind speed change is also allowed as the tower wake entrance condition in addition to the negative change observed in the previous model. It demonstrates better agreement with a wind tunnel test and contributes to the accuracy of the fatigue load, as it expresses a slight increase in load around the entrance of the tower wake. Furthermore, the scale effects are also evaluated; lift deviation becomes smaller as the scale increases, i.e., lower rotor speed.
Highlights
Upwind turbines, which have rotors in front of the towers, have been predominant throughout the decades of commercial wind turbine history
Downwind turbines can be advantageous in floating offshore wind turbine (FOWT) applications, so the share of the downwind rotor is much higher in FOWTs [3,4,5]
The tower wake is represented by the average wind speed profile with the turbulence ignored, and the trailing vorticity does not affect the lift of the blade element
Summary
Upwind turbines, which have rotors in front of the towers, have been predominant throughout the decades of commercial wind turbine history. Downwind turbines, which have rotors behind the towers, are gathering attention due to their technical and economic advantages regarding modern/future wind turbines. Downwind rotors generally have negative rotor tilt to avoid collision of the blade and the tower. One of the advantages of downwind turbines is performance in complex terrains. The negatively tilted rotors of downwind turbines are favorable for upflow wind in complex terrain [1]. Downwind turbines can be advantageous in floating offshore wind turbine (FOWT) applications, so the share of the downwind rotor is much higher in FOWTs [3,4,5]
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