AEROACOUSTICS

Nicholas Hamilton nicholas.hamilton@nrel.gov

Project start date 2019/07/01

NREL aeroacoustics project

Overview

The aeroacoustic emissions of a utility-scale wind plant operating under active plant-level controls will be assessed as part of the ongoing NextEra field measurement campaign. Whereas active plant control utilizing both wake deflection and induction control strategies have been shown experimentally and computationally to produce 1-2% of additional AEP without significant changes in turbine structural loads, the potential impact on aeroacoustic emissions has yet to be quantified or completely understood. Active manipulation of turbine wakes is achieved by operating turbines at off-nominal set points, which necessarily impacts the 3D aerodynamic operation of the blades. Power losses induced by implementing wake control strategies on particular turbines are outweighed by the gains derived for other turbines in a wind plant by mitigating wake interaction, thereby elevating the total energy extraction of the wind plant as a whole.

Off-nominal rotor control by yaw, thrust, pitch angle and/or rate of rotation is likely to induce local flow separation along the rotor blades and change the aerodynamic interaction with the local flow field. The extent to which active control induces additional aeroacoustic emissions from additional separation and other flow interaction dynamic effects must be quantified and any potential conflicts with limitations resolved. Given public concerns about wind turbine noise and the need for observational data required for regulators to establish noise restrictions, potential acoustic emissions resulting from active control must be understood prior to commercial deployment and the development of practical noise reduction methods and technology. Additional acoustic propagation effects introduced by active yaw and or thrust control must be investigated and understood for modern wind plant control strategies to be successfully implemented at the utility scale.

Program Goals:

• Determine the degree to which implementation of active wind plant control adversely impacts wind plant aeroacoustic emissions and limits the viability and deployment of active control and increased AEP.
• If active wind plant control is found to have significant aeroacoustic emissions impacting public acceptance and potential deployment, develop an R&D strategy to assess the underlying physics driving emissions and alternative mitigation strategies.

Program Objectives:

• Quantify experimentally the operational acoustic emissions resulting from two utility scale turbines operating under active wind plant control paradigms and ascertain the extent to which nominal operating emissions are exceeded.
• Calibrate an existing empirical acoustic propagation model to determine the impacts of a fully implemented active wind plant control deployment utilizing acoustic emission data obtained from experiment.
• Assess current experimental capability using phased acoustic arrays to identify sources of emission from active control implementation on rotors for future mitigation quantification.

Field Team

• Ben Anderson
• Nicholas Hamilton
• David Jager
• Jason Roadman
• Eric Simley

Modeling Team

• Pietro Bortolotti
• Yi Guo
• Pat Moriarty