Workshop at PoliMI

Monday October 12, 2015 10:06

From October 5 to 7, 2015, representatives of ECN, GE, NTUA, and PoliMi gathered in Milan in order to investigate root causes for disagreements in predictions for system stability as previously observed in work packages 1 and 4. Participants analyzed simplified instances of the AVATAR blade/rotor system before and during the workout in order to drill down on differences in methods and modelling, relevant to blade edgewise vibration in stand-still, and rotor instabilities in normal operation.

Agreement in the four lowest frequency bending mode natural frequencies is acceptable, but twist components based on Euler-Bernoulli beams were only half as large as those derived using higher order beam models - this is remarkable as twist was identified in D4.1 as having significant influence on damping of the first edgewise mode. Damping of this mode in the 20° to 100° angle of attack regime, predicted using quasi-steady aerodynamics, ranged from -1% to -3%. Including dynamic stall models amplified disagreement in post-stall regimes, re-emphasizing the lack of “ground truth” validation data in this area (possibly from New Mexico). Rotating blade and simplified wind turbine stand-still & normal operation simulation results were collected, but cross-comparison was incomplete due to time constraints. 

Participants will apply gathered knowledge to refine assessment of the impact of blade twist, quasi-steady polars, dynamic stall model, and stability prediction after the workshop.