Community Research and Development Information Service - CORDIS

Abstract

"For variable speed wind turbines it is possible to perform both a power control and a safety function using centrifugally controlled tips. Present mechanisms (screw-cylinder/spring type) are expensive and maintenance critical. A possible solution to these problems can be achieved with a so-called TenTorTube (Tension-Torsion Tube): a tube with inherent coupling between tension and torsion.

The objective of the project is to obtain reliable predictions on performance and stability and information on costs and applicability of the configuration by developing and testing a full-scale TenTorTube tip mechanism.

The initial proposed design of the TenTorTube was a long slender tube made of aramid fibre reinforced epoxy with an inherent coupling between tension and torsion. During the first phase of the project it became clear that the fatigue properties of aramid/epoxy were dramatically bad due to a creep-like behaviour. Tests on carbon/epoxy tubes showed an considerable increase in design strength, but not in torsional stiffness. Results of non-linear prediction of aeroelastic stability and performance showed poor stability and power limiting capabilities, mainly caused by the low torsional stiffness. Wind tunnel tests were carried out using a 2 degree of freedom model with an active control loop to simulate the TenTorTube properties like stiffnesses, damping etc. The wind tunnel tests confirmed the results obtained by the aeroelastic stability predictions.

The torsional stiffness requirement can not be met with the initially specified wind turbine configuration (250 kW - 2 bladed). An alternative (conceptual) design was generated, but was rejected. A parameter study showed that for 3 bladed turbine configurations with an increased ratio between maximum rotor speed and rated rotor speed, a feasible TenTorTube design was possible. Tower fatigue loads will however be larger which will result in more expensive towers for medium-sized wind turbines.

Resulting

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