Influence of rotor solidity on trailing edge noise from wind turbine blades

Abstract

Noise prediction from streamlined bodies such as wind turbine blades can be predicted accurately using CFD computations that use spatio-temporal turbulence models at the expense of high computational power. In this work, empirical methods proposed from BPM, Grosveld and Lowson are used to compute numerically to analyse the influence of rotor solidity factor on broadband trailing edge noise from a 2 MW horizontal axis wind turbine with a blade length of 37 m. Inputs to acoustic solver are the velocity vector field and boundary layer data which are obtained using blade element momentum and X-Foil. The outputs from acoustic solver are directivity and far field sound pressure on a receiver located at distance of 120 m from tower base. The results have shown that for a wind speed of 10 m/s measured at 10 m above ground, sound power level was found to increase between mid-bands to high frequencies for all three methods. Rotor solidity effect was illustrated at constant rotational speed of 17 RPM and receiver height of 0.5 m located in downwind position. A minimum difference of 1.5dBA was found at f ~ 100 Hz for Lowson method and maximum of ~ 2.8dBA at 1 kHz between two and three blade rotor. For BPM and Grosveld methods however, the sound levels were ~ 5dBA lower for two blade rotor than three blade rotor between f ~ 100 Hz and f ~ 1 kHz. The study also demonstrated that as number of blades increase by integral multiples, the effect on noise radiation from trailing edge of blades increase by 2-5dBA due to amplitude modulation.

Prediction of Atmospheric Turbulence Characteristics for Surface Boundary Layer using Empirical Spectral Methods

“…This plays critical role in turbines structural response and estimation of fatigue and extreme loads behavior in turbine design (Shigeo and Metwally, 2018) For instance, fatigue study by Shigeo and Metwally (2018) showed that a small increase in turbulence intensity level, from 1% to 10%, a significant reduction of time to failure of wind turbine components were observed. Particularly blades of wind turbine are more sensitive to turbu- lence and subjected to higher fluctuating loads (Bhargava et al, 2020;Nukala and Maddula, 2020;. Further, the damage equivalent loads (DEL) predicted by Von Karman and Kaimal turbulence spectra in the study were found to agree within 5% of peak values for different turbulence intensities.…”

A Study of High Lift Aerodynamic Devices on Commercial Aircrafts

“…The thin shear layer emanating from the slat cusp and its subsequent reattachment upstream of the slat trailing edge produces broad-band noise. Finally, tonal noise produces narrow band peaks whose amplitudes are function of characteristic trailing edge geometry, angle of attack, Reynolds number, Strouhal number and state of the boundary layer flow (Nukala & Maddula, 2020). Further, a tonal noise peak is quite often associated with vortex shedding behind a slat trailing edge with a finite thickness and produced due to stall separation inside the slat cove region.…”