Abstract
This paper presents a combined experimental and numerical study that characterises the directivity of blade-tower interaction (BTI) noise. Numerical computations were performed using a hybrid approach combining unsteady Reynolds-averaged Navier-Stokes equations and Curle's acoustic analogy, allowing the noise from the blades and the tower to be computed separately. The noise directivity of the blade and the tower components have a dipole pattern and a monopole-like pattern, respectively; hence, the resulting BTI noise directivity resembles an oval. Partial cancellations between the blade and tower components are also shown to affect the BTI noise directivity.
Highlights
Rotor-structure interactions play an important role in performance, structural integrity, and noise generation of the machinery involved.[1]
This paper presents a combined experimental and numerical study that characterises the directivity of blade-tower interaction (BTI) noise
As recent studies have suggested, the amplitude of the force fluctuations on the tower was found larger than that of the blade in both configurations
Summary
Rotor-structure interactions play an important role in performance, structural integrity, and noise generation of the machinery involved.[1] In the case of wind turbines, the interactions are between the turbine blades and their supporting tower.[2] This aerodynamic noise due to the unsteady interaction between turbine blades and a tower is referred to as blade–tower interaction (BTI) noise. BTI noise is generated by the change in loading on the blades and tower. Its acoustic signature is an acoustic pulse occurring each time a blade passes the tower; its frequency depends on the rotational speed and the number of blades, which is commonly referred to as the blade-passing frequency (BPF). As BTI generates noise at the BPF and its harmonics, it typically falls in the infrasound and low-frequency range. Due to the impulsive nature of BTI noise, the acoustic spectra typically consist of a tonal peak at the BPF accompanied by additional peaks at its higher harmonics.[3–5]. Due to the impulsive nature of BTI noise, the acoustic spectra typically consist of a tonal peak at the BPF accompanied by additional peaks at its higher harmonics.[3–5] The high levels of the harmonics suggests that the BPF is in the infrasound range, the harmonic tones may be within the audible frequency range of human hearing
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