Impact of turbulent inflow and orography on the low-frequency noise sources of a wind turbine

Abstract

A high-fidelity process chain is used to numerically investigate the low-frequency emissions from a generic wind turbine under turbulent inflow conditions. It consists of the Computational Fluid Dynamics (CFD) solver FLOWer, which is coupled to the multi-body simulation software SIMPACK to take unsteady aeroelastic effects into account. A realistic flow field for the complex terrain of Perdigão, Portugal is obtained by including the orography and vegetation in the simulation and using a precursor simulation with E-Wind to generate a site- and situation-specific inflow. The acoustic emissions are calculated with the Fflowcs-Williams-Hawkings (FW-H) acoustic solver ACCO. The simulations show that the tower emits noise caused by the blade-tower interaction (BTI) equally strong in all directions. To the sides of the turbine, this contribution is dominant, regardless of the turbulent inflow. The blades, on the other hand, emit significantly more noise under turbulent inflow, especially in streamwise direction, where they become the dominant source. The main noise mechanism here is the low-frequency part of the inflow turbulence (IT), followed by the BTI. The flow field in Perdigão causes additional large-scale variations in IT noise over time.

Assessment of low‐frequency aeroacoustic emissions of a wind turbine under rapidly changing wind conditions based on an aero‐servo‐elastic CFD simulation

“…This is computationally unfeasible for complex flow situations. 22 Therefore, semiempirical models for the noise sources based on flow parameters can be used to estimate the noise emissions, as presented in Cheng et al 23 in a state-of-the-art framework.…”

“…The author's previous works 22,24 on low-frequency noise emissions from WTs deal with flow situations in complex terrain. They investigate the impact of turbulent wind fields with constant mean wind speed and direction and thus constant operating conditions on the surface pressure fluctuations and the resulting noise emissions, respectively.…”

“…The highest captured frequency is limited by the CFD time step and mesh resolution to f < 20 Hz. 22 F I G U R E 1 Diagram of the numerical process chain.…”

“…In order to extend the frequency range with this numerical approach, the spatial and temporal resolution of the CFD simulation must be refined accordingly. This is computationally unfeasible for complex flow situations 22 . Therefore, semiempirical models for the noise sources based on flow parameters can be used to estimate the noise emissions, as presented in Cheng et al 23 in a state‐of‐the‐art framework.…”

“…They investigate the impact of turbulent wind fields with constant mean wind speed and direction and thus constant operating conditions on the surface pressure fluctuations and the resulting noise emissions, respectively. In Wenz et al, 22 among other things, the characteristics of the noise spectrum are analysed, with tonal peaks at the blade passing frequency (BPF) and its harmonics due to the BTI, which depend on the rotational speed, and the broadband level associated with the IT. Moreover, the directivity of the different noise sources (BTI, IT, VS) is presented in polar plots to analyse the underlying mechanisms.The aim of the simulation in this article is to extend these works and investigate the low‐frequency noise emissions of a wind turbine under rapidly changing wind conditions (unsteady operating conditions).…”