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Theoretical and experimental investigations on a one-bladed medium size wind turbine to improve the design criteria for larger units


Definition of a new concept for the flap control subsystem of a single-bladed WTG. Assessment of fatigue behaviour of some WT structural parts in real operating conditions. Calibration of two verification procedures against fatigue in single-bladed WTGs: the general extensive one from Garrad and Hassan and the simple codified one adopted by MBB and Riva Calzoni.
A theoretical and experimental investigation project on a single bladed wind turbine was started.

To carry out the experimental data for both the verification of the aeroelastic codes and the strain measurements on the nacelle frame, the data acquisition system had to be extended. The improvements consisted in the installation of further sensors, modifications in the signal conditioning and a new setup of the recording devices. In November 1991 the duty cycles needed for the research activities, consisting in a 10 minutes record at the rated wind speed, 10 minutes at high wind speeds and a record of an emergency shut down were executed. The recorded data have been post processed and are now in use.

In the meantime the aeroelastic code of Garrad Hassan and Partners (GH&P) was adapted to single bladed wind turbines and its verification is being finalized. This tool together with the hub load nacelle frame strain transfer matrix makes it possible to predict the damage rates in the hot points of the nacelle frame. Some simulations of the emergency shut down transient were executed with the aim of deepening the understanding of the flap behaviour. Probably this knowledge could lead to important improvements on the M30 wind turbine (WT) related to a simplification or even to the elimination of the flap damping device.

Theoretical considerations on the high wind shear approach indicated that the method will not lead to good results for the flat wise blade load estimation. This could be confirmed by the comparison of the results with the ones obtained with a 3-dimensional turbulence model.

Because the high wind shear approach means an important simplification for the design with respect to fatigue loads, it will be interesting to verify if the approach is valid for the rest of the WT structure.
The work will be carried out on the M30 first prototype installed in the Alta Nurra ENEL test field (Sardinia); it is divided into three parts.

1) Preparation activities The measuring system of the unit will be improved, in order to allow an appropriate measuring activity. Measurements will be performed both in steady state and in transient operation conditions.

2) Flap system Iterative Optimization The goal of the procedure is the definition of a solution for a completely passive and safe flap system for a single blade WT. A specific test campaign is foreseen to check the behaviour of the new solution in real operating conditions.

3) Fatigue Assessment A nacelle frame identical to the prototype one will be statically loaded during shop test, meant to identify the transfer functions between loads in the rotor centre and strains in some hot points of the structure. In the same hot points, strain measurements will be made on the unit in operating conditions. The transfer matrixes will allow direct simple computation of the stresses in the hot points, coming from computed loads and accelerations combinations. Fatigue damage rates will be derived on the basis of the existing regulations for each hot point, by using measured data. In the same way, but with predicted stress-time hysteresis the fatigue damage rates will be computed. Then a fully comprehensive comparison can be performed between the fatigue life of the structure deriving from both measured strain data and theoretical results. The design codified approach adopted by Riva Calzoni and MBB in the development can be compared, step by step, with the experimental results, with the elp of the theoretical approach. The optimization of the codified method is the final goal and it can be used as a basis for more general guidelines.


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Riva Calzoni SpA
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Via Stendhal 34
20144 Brunico

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