Bladed versions affected: all Bladed versions supporting dynamic stall calculations.
Date of last article update: 27 February 2024
BEM-based aero-elastic models have significant uncertainties when the sectional airfoil sections are exposed to high angles of attack. This is especially true when the unsteady effects are strong, e.g., exposed to a continuous change of the angle of attack due to turbulence. These conditions typically occur in design load case (DLC) of the turbine in standstill, either as parked or as idling in DLC 6.1, DLC 6.2 and DLC 6.3 or in case the turbine shuts down in DLC 1.4. Aerodynamic behavior at high angles of attack is more complex and good experiments and measurement campaigns are difficult to perform. Consequently, there is a wider range in loading predicted by the different models. The following aerodynamic aspects are to be considered when using Bladed for such cases:
1. The IAG dynamic stall model is recommended for simulations under stand-still conditions (parked or idling). The model captures the hysteresis of the aerodynamic forces with good accuracy compared to measured pitching airfoil data at high angles of attack, better than other dynamic stall models in Bladed. Studies show that blade vibrations are smaller when using the IAG dynamic stall model under stand-still conditions at yaw angles of about 30-60 degrees, where instability usually occurs. Please refer to the following articles for more information:
- Technical modeling challenges for large idling wind turbines
This model is only available from Bladed 4.14 onward (version starting from 4.14.0.3 is suggested). For older versions of Bladed, the recomended practice Nr. 4 below is suggested.
2. Only the first order stall model is adopted in Bladed, thus higher harmonic effects like airfoil vortex shedding or 3D affects are not modeled.
3. Double check if the number of blade structural parts is sufficient to model flexible blades. Sensitivity studies might be required.
4. If unrealistic vibration still occurs, it is a general practice to increase the structural damping of the first edgewise mode. Note that a sensitivity study might be required to properly scale up the value of the edgewise damping.