Experimental and Numerical Vibrational Analysis of a Horizontal-Axis Micro-Wind Turbine

Francesco Castellani,Alessandro Cetrini,Filippo Cianetti,Matteo Becchetti,Francesco Berno,Davide Astolfi

doi:10.3390/en11020456

Abstract

Micro-wind turbines are energy conversion technologies strongly affected by fatigue, as a result of their size and the variability of loads, induced by the unsteady wind conditions, and modulated by a very high rotational speed. This work is devoted to the experimental and numerical characterization of the aeroelastic behavior of a test-case horizontal-axis wind turbine (HAWT) with a 2 m rotor diameter and a maximum power production of 3 kW. The experimental studies have been conducted at the wind tunnel of the University of Perugia and consisted of accelerometer measurements at the tower and the tail fin. The numerical setup was the Fatigue, Aerodynamics, Structures, and Turbulence (FAST) code for aeroelastic simulations, which was fed as input with the same wind conditions employed in the wind tunnel tests. The experimental and numerical analyses were coupled with the perspective of establishing a reciprocal feedback, and this has been accomplished. On one hand, the numerical model is important for interpreting the measured spectrum of tower oscillations and, for example, inspires the detection of a mass unbalance at the blades. On the other hand, the measurements inspire the question of how to interpret the interaction between the blades and the tower. The experimental spectrum of tail fin vibrations indicates that secondary elements, in terms of weight, can also transmit to the tower, giving meaningful contributions to the vibration spectra. Therefore, an integrated numerical and experimental approach is not only valuable but is also unavoidable, to fully characterize the dynamics of small wind-energy conversion systems.

Highlights

Micro-wind turbine technology stands at the crossroad of diverging demands
Most of the experimental tests were conducted using the ramp wind time series, because it explores monotonically all the rotational speeds and provides a very clearly understandable framework: all the results reported in this work, except where otherwise explicitly declared, refer to a ramp time series increasing from 6 to 11 m/s with a 1 m/s increase over about 14 s
The objective of the work was the comprehension of the tower and tail fin vibration spectra of the test-case horizontal-axis wind turbine (HAWT) in operation

Summary

Introduction

Small wind turbines should be sufficiently simple, in order to be used by people without technical expertise [1], and their control system should be smart. Their design [2,3,4] and control [5,6] should be sufficiently advanced, in order to obtain a certain degree of efficiency in converting and exploiting wind kinetic energy, counteracting a certain prejudice that micro-wind turbine technology performs poorly [7]. The use of micro-wind turbines in urban environments, where the average wind intensity is commonly quite low and the turbulence structure might be complex, requires the optimization of the design of the blades [4] and of the performances near the Energies 2018, 11, 456; doi:10.3390/en11020456 www.mdpi.com/journal/energies

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Conclusion