Blade forces

US researchers have developed a technique that uses sensors and software to constantly monitor forces exerted on wind-turbine blades.


The research by engineers at Purdue University and Sandia National Laboratories is part of an effort to develop a smarter wind-turbine structure.


‘The ultimate goal is to feed information from the sensors into an active control system that precisely adjusts components to optimise efficiency,’ said Purdue doctoral student Jonathan White, who is leading the research with Douglas Adams, a professor of mechanical engineering and director of Purdue’s Center for Systems Integrity.


The system could also improve wind-turbine reliability by providing critical real-time information to a control system to prevent catastrophic wind-turbine damage from high winds.


The engineers embedded sensors called uniaxial and triaxial accelerometers inside a wind-turbine blade as the blade was being built.


The blade is now being tested on a research wind-turbine at the US Department of Agriculture’s (USDA) Agriculture Research Service laboratory in Bushland, Texas.


Personnel from Sandia and the USDA operate the research wind-turbines at the Texas site.


The sensors are capable of measuring acceleration occurring in various directions, which is necessary to accurately characterise the blade’s bending and twisting and small vibrations near the tip that eventually cause fatigue and possible failure.


The sensors measure two types of acceleration.


One type, the dynamic acceleration, results from gusting winds, while the other, called static acceleration, results from gravity and the steady background winds.


It is essential to accurately measure both forms of acceleration to estimate forces exerted on the blades.


The sensor data reveal precisely how much a blade bends and twists from winds.


Research findings show that using a trio of sensors and ‘estimator model’ software developed by White accurately reveals how much force is being exerted on the blades.


‘The aim is to operate the generator and the turbine in the most efficient way, but this is difficult because wind speeds fluctuate.


‘You want to be able to control the generator or the pitch of the blades to optimise energy capture by reducing forces on the components in the wind turbine during excessively high winds and increase the loads during low winds.


‘In addition to improving efficiency, this should help improve reliability,’ Adams said.


The research is ongoing, and the engineers are now pursuing the application of their system to advanced, next-generation turbine blades that are more curved than conventional blades.


This more complex shape makes it more challenging to apply the technique.