Insights into the Aeroacoustic Noise Generation for Vertical Axis Turbines in Close Proximity

Abstract

We present Large Eddy Simulations and aeroacoustic spectra for three configurations of increasing flow complexity: an isolated NACA0012 airfoil, an isolated rotating vertical axis wind turbine composed of three rotating airfoils and a farm of four vertical axis turbines (with identical characteristics as the isolated turbine), which are located in close proximity. The aeroacoustic signatures of the simulated airfoil and the isolated turbine are validated using published numerical and experimental data. We provide theoretical estimates to predict tonal frequencies, which are used to identify the main physical mechanisms responsible for the tonal signature and for each configuration and enable the categorisation of the main tonal aeroacoustic sources of vertical axis turbines operating in close proximity. Namely, we identify wake, vortex, blade passing and boundary layer phenomena and provide estimates for the associated tonal frequencies, which are validated with simulations. In the farm, we observe non-linear interactions and enhanced mixing that decreases tonal frequencies in favour of larger broadband amplitudes at low frequencies. Comparing the spectrum with that of the isolated turbine, only the blade passing frequency and the boundary layer tones can be clearly identified. Variations in acoustic amplitudes, tonal frequencies and sound directivities suggest that a linear combination of sources from isolated turbines is not enough to characterise the aeroacoustic footprint of vertical axiswind turbines located in close proximity, and that farms need to be considered and studied as different entities.

A Ffowcs Williams-Hawkings numerical aeroacoustic study of varied and fixed-pitch blades of an H-Rotor vertical axis wind turbine

“…(2) The impact of the varied angle of attack on the tip speed ratio improves the turbine's power efficiency and torque output. However, the downstream and upstream noise intensifies as the angle of attack increases [21]. As a result, noise prediction at take-off must account for the effect of angles of attack.…”

Machine-Learning Methods for Complex Flows

“…The sixth article is entitled "Insights into the aeroacoustic noise generation for vertical axis turbines in close proximity" by Viqueira-Moreira and Ferrer [36]. In this article, the authors predict tonal frequencies, providing theoretical estimates in: an isolated NACA0012 airfoil, an isolated rotating vertical axis wind turbine composed of three rotating airfoils, and a farm of four vertical axis turbines.…”

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“…Recently, Kun Wang et al examined the instability characteristics of a twin-turbine (vertical axis) wake with two rotational configurations and reported that the inverse energy cascade process occurs after high-frequency coherent structures [12]. The aeroacoustics signatures of the VAWT are examined using large-eddy simulations and aeroacoustics spectra for different configurations [13]. Particularly, it is stated that the VAWT model is capable of capturing wind from any direction [14,15].…”