Failures of wind turbines
Author: Kleeman, Dick
I would like to comment on the growing number of failures of wind turbines and point out the reason why this is happening, and how you may be able to use this further information in stopping this proliferation wherever it arises.
I believe there is a fundamental problem with all large wind turbines which cannot be solved by those designing and building them. It is not possible to build large blades like those occurring now, that can withstand the forces they will be subjected to without continuing to increase the size and strength of the materials but this then becomes diametrically opposed by the centrifugal forces the increase causes.
It is well known that flywheels will disintegrate if the speed exceeds certain limitations owing to their mass. Apart from that consideration the gust factor in high winds over time will be a primary consideration in the blade failing and the rest of the structure. It is mandatory for light aircraft propellers to be overhauled and tested after 2000 hours because of the fatigue problem and they are far stronger for their size than any wind turbine blade.
As a retired Australian airline pilot I can say from first hand experience that the majority of people do not have an appreciation of the dangers and forces that are associated with well developed thunderstorms and this is now evident as regards the engineers designing wind turbines. To think that you can design an eighty to one hundred and twenty metre diameter set of blades, attached to a fixed tower and not get structural failure in severe weather is to not understand the problem.
The coefficient of lift reaches a maximum at 16 degrees with the airflow over an aerofoil and at that critical angle of attack, stall buffet and turbulence occur. Because with the passage of a storm the wind does not blow at a constant speed or from a uniform direction, the gust can hit the blades from different directions and speeds at the same time. This will cause stall flutter which is an aerodynamic load and twisting moments on the blade that can exceed any design limit that can be built for a given size.
When a thunderstorm passes, the wind veers through 180 degrees and under an active cell the downbursts can exceed 200 miles per hour as well as being accompanied by lightning and hail. I strongly challenge any mechanical engineer, even though I am not one, that they can guarantee a braking system that will feather the blade and lock the shaft in most cases when hit with these sorts of forces.
To give an example of the forces associated with downbursts, there are numerous histories of accidents where large passenger jets have tried to take off and land under thunderstorm cells and to suggest that a wind turbine structure can withstand this exposure over time is absurd. It is my opinion that the increasing number of blade failures will be traced to exposure to high wind gust exposure without even taking into account lightning and hail effects. At any given time around the globe there are about 50,000 active storms, some of which can even develop into tornadoes.
Hurricanes and ice storms have not been mentioned here but the same forces apply.
Tags: Wind power, Wind energy
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