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

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.

The Yawing Behavior of Horizontal-Axis Wind Turbines: A Numerical and Experimental Analysis

“…A full-scale three-bladed HAWT having 2 m of rotor diameter has been selected as a test case for this work, also on the ground of previous studies (Scappaticci [29], Castellani [31], Castellani [32]) characterizing its design, control and vibration behavior under steady and unsteady conditions. A measurement campaign has been conducted in the wind tunnel of the University of Perugia and the experimental conditions have been replicated using two simulation frameworks: the aeroelastic software FAST, developed at the NREL, and an ad hoc developed code based on Blade Element Momentum Theory.…”

“…This is explained by the higher distance between the tower and the blade surface in the yawed cases. Sideways, since the tower interference is difficult to model in FAST for small HAWTs (as discussed, for example, in Castellani [31]), this possibly explains why the discrepancy between simulated and measured C T is higher when the yaw angle vanishes and the tower interference is maximum.…”

“…From Figures 9 and 10, the different dynamic performance of the two measuring equipment also arises: accelerometers are much more sensible in observing how the dynamic loads components change when the turbine is yawed, even if they could be affected by noise arising also from electromechanical couplings (Castellani [31]). The error in the amplitude of the experimental and numerical accelerations is biased mainly by the effect of the electromechanical coupling (that is actually not correctly reproduced in FAST as discussed, for example, in Castellani [31]). Consequently, the effect of the yaw has been discussed in Figure 9 using a normalized amplitude.…”

“…The test case is a three-bladed horizontal-axis wind turbine HAWT having two meters of rotor diameter: this prototype has been selected because it has been possible to employ it for full-scale tests in the wind tunnel of the University of Perugia. Furthermore, previous studies had been conducted about the dynamical behavior of this wind turbine, especially as regards vibrations and control (Scappaticci [29], Castellani [30], Castellani [31], Castellani [32]). Sideways, the study of the control and of the performance of small HAWT technology has recently been attracting attention in the scientific literature, especially as regards the interaction with complex ambient conditions (as, for example, urban environment: see Battisti [33], Balduzzi [34], Bianchi [35], Balduzzi [36]).…”

Mechatronic Modeling and Frequency Analysis of the Drive Train of a Horizontal Wind Turbine

“…The second was to use that model to determine analytically the number and the value of the resonance frequencies from the generator angular velocity in such a way that such information could be used by any control algorithm or even by the mechatronic system designers. We assessed through experimental validation using a real 100 kW wind turbine that these two objectives were reached, demonstrating that the different vibration modes were detected using only the generator angular velocity.The main objective of wind turbines is to extract the maximum amount of energy from wind [2,3], taking into account both the environmental [4] and economic effects [1,5], and avoiding resonances in the tower and the rest of the structure [6,7]. Mechanical fatigue can cause wear of elements of the nacelle and the tower, which in turn can cause resonances with the consequent breakage of elements, losing power performance and decreasing safety [8].…”