Dr. Markus Schmid, CTO fos4X GmbH
With the updated IEC standard 61400-13 from the year 2015, the measurement of new wind turbines places greater demands on the detection of the blead loads. Load measurements on the rotor blade root, the measurement of the load distribution and the torsional frequency are required. IEC 61400-13 requires that the sampling rate is at least eight times the highest signal frequency.
We provide a standard configuration to fully meet these requirements. The advantages of fiber-optic strain sensors with regard to electrical strain gauges lie in the significantly shortened installation period and in the possibility of reliably measuring high strain amplitudes (> 0.3%).
Together with our partner imc Test & Measurement, we also offer a complete solution with the software imc Studio. A partial requirement for prototype measurements is, in addition, an overload shutdown and/or tower enable measurement, which can also be realized based on our data.
More than 250 sensors in one rotor have already been developed to investigate the neuralgic points of a new blade design.
With longer rotor blades, torsional vibrations and torsional-bending couplings play an important role in the development.
We use a number of fiber-optic temperature sensors distributed in the rotor blade to evaluate the blade heating.
Over 250 sensors in one rotor we have realized in a project in China to investigate neuralgic points of a new blade design. In the project a total of seven measuring instruments – six for quasi-static measurement and one for dynamic measurements – were used. 132 Mini-strain sensors were used to make a strain field for aeroelasticity studies on a newly developed rotor blade.
In addition to the distributed strain sensors, fiber-optic rotor blade sensors were used to measure shear stresses, vibration behavior and temperature in this challenging project.
With longer rotor blades, torsional vibrations and torsional bending couplings play an important role in the development. In this project, a total of eight torsion sensors were used on different blade radii together with a shear stress sensor as well as strain sensors.
In addition to the investigation of the relationship between the bending line and torsion, the study of the torsional vibrations at different radii also played a major role in this specific project in Texas, USA.
For the evaluation of blade heating systems we successfully use distributed, optical temperature measurements. Just as with the distributed strain measurement, it is also possible to measure temperatures at many points in the rotor blade and in this way to determine the precise distribution of the temperature during heating processes.
A specific project involved, among other things, to calibrate the FEM flow model in the blade so that further structural improvements could be made to improve the efficiency of the blade heating system on the computer.
Future, intelligent rotor blades will need pressure sensors – now they are used to measure the flow and to optimize noise emissions.
In a large-scale project to investigate the flow behavior, we used 150 pressure sensors at several radii on the outside of a rotor blade. In addition, the blade was equipped with various structural sensors. With the setup, the emergence of turbulence on the blade surface, barn development and the noise emission could be precisely investigated.