Analysis of throw distances of detached objects from horizontal-axis wind turbines 

Figures 4 to 6 show the results for different-size blade pieces from different-size turbines at different wind speeds and blade tip speeds. For normal tip speeds (figs 4 and 5), the potential blade throw distance for a 2.3-MW turbine was calculated to be ~500 m (1,640 ft) and for a 5-MW turbine ~900 m (2,953 ft). At “extreme” tip speeds (fig 6) the corresponding distances were 800 m (2,625 ft) and 1500 m (4,921 ft).

[ABSTRACT] This paper aims at predicting trajectories of the detached fragments from wind turbines, in order to better quantify consequences of wind turbine failures. The trajectories of thrown objects are attained using the solution to equations of motion and rotation, with the external loads and moments obtained using blade element approach. We have extended an earlier work by taking into account dynamic stall and wind variations due to shear, and investigated different scenarios of throw including throw of the entire or a part of blade, as well as throw of accumulated ice on the blade. Trajectories are simulated for modern wind turbines ranging in size from 2 to 20 MW using upscaling laws. Extensive parametric analyses are performed against initial release angle, tip speed ratio, detachment geometry, and blade pitch setting. It is found that, while at tip speeds of about 70 m/s [157 mph] (normal operating conditions), pieces of blade (with weights in the range of approximately 7-16 ton) would be thrown out less than 700 m for the entire range of wind turbines, and turbines operating at the extreme tip speed of 150 m/s [336 mph] may be subject to blade throw of up to 2 km from the turbine. For the ice throw cases, maximum distances of approximately 100 and 600 m are obtained for standstill and normal operating conditions of the wind turbine, respectively, with the ice pieces weighing from 0.4 to 6.5 kg. The simulations can be useful for revision of wind turbine setback standards, especially when combined with risk assessment studies.

Hamid Sarlak and Jens N. Sørensen
Section of Fluid Mechanics, Department of Wind Energy, Technical University of Denmark, Lyngby, Denmark

Wind Energy 2016; 19:151–166. DOI: 10.1002/we.1828

Download original document: “Analysis of throw distances of detached objects from horizontal-axis wind turbines”

See also: 

• “A method for defining wind turbine setback standards” by Jonathan Rogers, Nathan Slegers, and Mark Costello, Wind Energy 2012; 15:289–303. (463 m [1,519 ft] for a Vestas 2-MW turbine)

• “Analysis of blade fragment risk at a wind energy facility” by Scott Larwood and David Simms, Wind Energy (published online 6 April 2018). “The results showed that a setback to property lines of 2 times the overall turbine height would be acceptable. However, the setback to dwellings should probably be increased from 3 to 3.5 times the overall turbine height for an acceptable risk.”