Wind Turbine Noise and How the Science Can Be Used to Determine the Impacts on People

Transcription

1 Wind Turbine Noise and How the Science Can Be Used to Determine the Impacts on People 2nd Int. Summer School on Stochastic Dynamics of Wind Turbines and Wave Energy Absorbers Aalborg DK Brüel & Kjær Sound & Vibration Measurement A/S. Copyright Brüel & Kjær. All Rights Reserved. Colin Novak PhD, PEng August 08, 2014

2 Agenda Introductions Social acceptance of wind turbine noise Technologies and their use to determine human impacts Sound Power (IEC ) measurements and propagation modeling Infrasound equipment and wind screens Wind farm noise and vibration management through permanent and continuous monitoring Case study of using Structural Analysis techniques to solve a tonal environmental noise problem Acoustic array measurement techniques Summary Additional Modal (OMA) Applications 2

3 Colin Novak PhD, PEng Professor, Mechanical Engineering (Acoustics). University of Windsor, Canada ( Present) Specialties include Psychoacoustics, Automotive NVH, Structural Vibrations, Environmental Noise and Wind Energy President, Akoustik Engineering Limited (2009- Present) On Sabbatical with Global Key Accounts, Bruel and Kjaer (2013/2014) 3

4 University of Windsor s Wind and Renewable Energy Centre of Expertise Valuable collaboration between B&K,the University of Windsor and Lund University Windsor area is an ideal location for the Wind Energy Centre Areas of research Environmental noise management of wind turbines Study of government guidelines and standards for environmental noise control Sound quality and noise measurement techniques for wind turbines Vibration monitoring and structural analysis of wind turbine towers and blades Emphasis of the centre is to advance graduate education 4

5 Wind Turbines within Society The use of wind turbines for electricity generation is fairly new but is expected to increase as governments move toward promoting greener energy sources. Advantages of Wind Energy Wind is a natural resource (free) Produces no air pollution or greenhouse gas emissions Delivers economic benefits to rural communities through investment, jobs, lease income for landowners etc. Disadvantages of Wind Energy Considered by many as an eyesore Safety concerns ice throw, blade and tower failure, wildlife Shadow flicker (approx. 1 Hz) Operational lifespan end of life costs Noise nuisance and perceived health affects Construction noise, maintance, decommissoning -Offshore 5

6 Canada: Electricity Amounts Generated from Wind 2013 World Wide Capacity was MW 6

7 Wind Turbines within Society Wind energy is generally viewed as a positive alternative to fossil and nuclear forms of energy Those opposed mostly consist of people directly affected by wind farm development Not in my backyard It is critical that a planning policy which regulates the process of wind farm development be in place consisting of: Background study Public consultation and involvement Development plan content objective statements, sensitive land use policy, zoning requirements including setbacks for noise and complaint management Technology needs to play a critical role in advancing the science of wind turbine noise management and to control the human impacts 7

8 Technologies for Determining Human Impacts Technologies and their use to determine human impacts Sound Power (IEC ) Measurements and Propagation Modelling Used mostly at the approval stage Noted to have significant short comings Infrasound Equipment and Wind Screens Positive advances in electronic equipment, but how do we deal with wind noise Wind farm noise and vibration management through permanent and continuous monitoring Technology is greatly under utilized Case study to solve tonal noise problem IEC , order analysis, ODS, OMA Acoustic Array Measurement techniques Technology is still advancing 8

9 IEC : Sound Power Measurement Purpose of standard: Provides uniform methodology to ensure consistency and accuracy in measurements Provides guidance in the measurement, analysis and reporting of complex acoustic emissions from wind turbine generator systems Will benefit those involved in manufacture, installation, planning and permitting, operation, utilisation and regulation of wind turbines Heavily used by environmental noise regulators for predicting future noise impacts at residential receptors 9

10 Process Chain for Measurements 10

11 IEC : Equipment Schematic 11

12 IEC : Microphone Positions Microphone Positions Primary position (1) is directly downwind +/- 15 degrees. Additional microphone positions at same distance R as primary position +/- 20%. Distance R=H+D/2 Full Coverage For Directivity For Sound Power 12

13 Windscreen For Boundary Layer Microphone 13

14 Measurement Overview Showing Actual Number of Measurements per Wind Class (Wind-bin) Time for individual measurements Wind-bin Electrical Power (P) in kw Sound power in db(a) Tonality penalty for each measurement KTN in db Impulsivity penalty for each measurement KTN in db Calculated wind speed in m/s 14

15 IEC : Typical Report 15

16 IEC : Short comings While the measurement procedure is well detailed, it is difficult to implement in practice Brings repeatability into question Implementation of calculated sound power data into noise propagation models is often criticized (ISO 9613) Procedure does not always measure for worst case Our studies have shown that maximum directivity is not always downwind, especially for lower wind speeds Method for determining tonality is complex and nonstandard 16

17 IEC : Summary Complete system developed in cooperation with wind turbine manufacturers Performs all the measurements Sound Power, Tonality, Impulsivity Optional: Directivity and Low frequency content Does all data reduction and bookkeeping Reports with full documentation of wind turbine and components Criticisms Very difficult to implement in practice Often not followed as prescribed Procedure does not always measure for worst case 17

18 Interface For Wind Turbine Data Input into Model 3D model with noise contours from wind turbines Wind turbine database with option to calculate sound power levels based on IEC The equivalent L W at turbine height is calculated based on various parameters including turbine height, cut-in speed, cut-out speed, etc. 18

19 Propagation Modeling of Wind Turbine Noise Impacts at Residential Receptors ISO , Acoustics-Attenuation of sound during propagation outdoors - most often used standard for determining residential noise impacts from turbines Describes a method for calculating the attenuation of environmental noise during propagation outdoors. It takes into account both environmental and ground conditions including: Geometrical divergence Atmospheric absorption Ground effects Screening Other miscellaneous effects The method predicts the resulting equivalent continuous A-weighted sound pressure level (LAeq). Not thought to be the best approach since it assumes an acoustical radiation near to ground height which is not the case. 19

20 Infrasonic Noise and its Perception Sounds below 20 Hz are referred to as infrasonic sounds and are mostly inaudible except at very high amplitudes. Infrasound is a controversial topic with respect to wind turbine noise impacts on humans At infrasonic frequencies, a sound moderately above the hearing threshold are perceived as being both loud and annoying. This gives rise to the feeling of discomfort to some. Infrasound has been shown to cause sleep difficulties, feelings of uneasiness, difficulty concentrating or performing tasks, headaches, dizziness and tinnitus. These, however, are usually associated with exposure to high levels of infrasound. Many studies have failed to show a definitive link between wind turbine noise and wind turbine syndrome. 20

21 Infrasonic Noise Measurement Microphones New hardware has been developed (Type 4964 Infrasound Microphone) to better measure infrasound 21

22 Comparitive Test of Low Frequency Microphones for Wind Turbine Noise Type 4193 w. UC 0211 Type 4964 Type 4189 A 021 Classic New Conventional 22

23 Infrasonic Noise Managing Wind Noise It goes without saying that wind turbine noise must be measured in the presence of wind, ie. without wind, the turbine would not be turning and producing noise Typical primary microphone windscreens are adequate for wind speeds up to 6 m/s However, often need to measure sounds with wind speeds as high as 12 m/s Wind has a large influence on infrasonic noise measurements Result is the need to use secondary wind screens 23

24 Infrasonic Noise Managing Wind Noise 24

25 Infrasonic Noise Managing Wind Noise 25

26 Human Perception of Infrasonic Noise Studies have found that attitudes toward the visual impact of wind turbines on their landscape were related to their annoyance; the more negative their visual perception, the greater their annoyance. These visual disruptions give an increased disposition to an increased risk of annoyance which may be confused with infrasound exposure. Given that wind turbines do not cease operation during night time, as is the case with traffic and industrial noise, a daily environmental change may not occur. Other studies have suggested that susceptibility to infrasound differs between individuals and is tied to a genetic disposition. Recommendations include increase setbacks to 1 km and lower limits to 35 dba. More study is needed to make definitive conclusions, however, a general reluctance is prevalent. 26

27 Environmental Noise Monitoring Environmental noise monitoring is recommended to be performed at nearby sensitive receptors to monitor the real time impact of turbine operations at receptors Often required for initial compliance but not applied often enough for continuous monitoring Equipment should comply with IEC Class 1 specifications. Noise monitoring can be: Short term, often between 24 hours to a week in duration Medium duration of one week to several months Permanent continuous long term monitoring Nacelle parameters can be integrated with the noise data Weather Turbine power Blade pitch etc. 27

28 Environmental Noise Monitoring using B&K Sentinel 2 minute resolution This example shows a specific turbine being monitored Ability to view: Hour Day Week Month 28

29 Environmental Noise Monitoring Short term noise monitoring Medium term noise monitoring 29

30 Environmental Noise Monitoring Permanent noise monitoring B&K Noise Sentinel does it all for you! Permanent installation with continuous noise (or vibration) monitoring capability and continuous communications to web based servers. Real time alerts for exceedences to allow for immediate operations abatement. Powered by Mains, solar or even hybrid solar/ wind power. Can be combined with weather, nacelle power data, blade pitch, security camera, etc. Low maintenance including self calibration. Can be used to continually monitor wind farm noise emissions at receptor locations and correlate noise with turbine data to optimize turbine operation while not exceeding noise guidelines 30

31 Environmental Noise Monitoring Noise Sentinel Monitoring Web Based Interface Locate noise monitors at residential receptors near wind farms 31

32 Noise Monitoring with Directional Capabilities It is sometimes difficult to distinguish between wind turbine noise and other sources which contribute to the soundscape. Wind farms may be wrongly blamed. Directional noise monitors can help identify the true source of excessive noise. 32

33 Noise Monitoring with Directional Capabilities 33

34 Case study: Solving a Wind Turbine Tonality Problem using Structural Analysis Problem: A newly developed wind turbine design did not pass noise certification (IEC ) due to a tonal noise problem. The tonal components in the radiated noise exceeded the allowed noise level. Noise can also be an indication of vibration issues leading to structural problems. 34

35 Measurements according to IEC Noise measurement reveled some tones which exceed the levels defined in the standard Brüel & Kjær applications

36 Power spectra from ground microphone This is a typical spectrogram at ground mic. Observations: two groups of tones which follow RPM fluctuations 36

37 Tonality profile Brüel & Kjær applications Pulse Reflex This is a tonality profile (tonality as a function of time) for the previous recording, calculated according to the IEC standard. Tones have a high penalization factor, which can seriously damage noise certification of a wind turbine By reducing these two tones, one may significantly reduce overall audible tonality. 37

38 Order analysis Frequency of the tone follows the RPM, thus order analysis was chosen as the appropriate investigation tool. Brüel & Kjær applications Pulse Order Analysis Frequency fluctuation in spectrogram (left) becomes a straight light in ordergram. It becomes clear that the tone corresponds to order XXp. The table of gearbox meshes points to the gearbox stage which is responsible for the tone. 38

39 Modal analysis In order to understand the resonance phenomena, a Modal Analysis was conducted. First an Operational Deflection Shape (ODS) analysis was performed. ODS animation Since the structure was too big for traditional modal analysis, an Operational Modal Analysis (OMA) was performed. The analysis revealed a mode at a frequency near to the problematic frequency. As it can be seen in the next video, the mode shape corresponds well to the ODS results and the problematic order. Mode animation 39

40 Modal analysis 40