Programme

Detailed programme

Thursday 17 November 2016 – 9:00 – 9:10

Opening Address – “The Polish context”, Magdalena Klera-Nowopolska, Environment & Development Department Manager, Polish Wind Energy Association (PSEW)

Thursday 17 November 2016 – 09:10 – 11:00
Session 1: Measurements

Session chair: Frederik Gast, Senior Expert Acoustics, Vibro-Acoustics and Technical Inspection, Windtest Grevenbroich GmbH
Speakers:

Thursday 17 November 2016 – 11:45 – 13:45
Session 2: Wind farm design & siting

Session chair: Tomas Blodau, Head of Department Wind and Site, Senvion
Speakers:

Thursday 17 November 2016 – 15:00-17:00
Session 3: Wind turbine design

Session chair: Roger Drobietz, Technical Leader Systems Performance, GE Wind Energy

 This session will provide a view on new technology developments for an improved sound characteristic of modern wind turbines. The focus is on blade technologies for lower sound levels as well as drive train technologies for lower tonal audibilities. In addition, the session will discuss experimental techniques and modelling approaches that shall support and enable an advanced turbine noise design. Sufficient time has been allocated for in depth discussion between the expert speakers and the audience.

Speakers:

19:00 Workshop Dinner for all participants

Friday 18 November 2016 – 09:00-11:00
Session 4: Human perception & guidelines

Session chair: Jeremy Bass, Head of Specialist Services, RES Ltd.

Speakers:

Intersession Presentation: New IEA Wind Task on Quiet Wind Turbine Technology

Niall McMahon, Lead Researcher, Distributed Wind Energy Group, Trinity College Dublin.

Friday 18 November 2016 – 11:45-13:30

Session 5: SPICE

Session chair: Matthew Cand, Associate Engineer, Hoare Lea Acoustics

Introduction: “SPICE Edition 1 – Presentation, Analysis and Perspectives”.  Frank Bertagnolio, Senior Scientist, DTU

Session description: Presentation of the Sound Propagation International Comparison Exercise (SPICE), overview of results, comparison and analysis of results, conclusions. Followed by open discussion with audience (e.g. comments on results, lessons learned, considerations about a future edition of SPICE, etc.) moderated by the session chair.

Abstracts

Session 1 – Measurements

Wind turbine excess noise big data analysis

Presenting Author: Marko Antila, Senior Scientist, VTT Technical Research Centre of Finland

Abstract: Earlier research on the wind turbine noise was carried in a national project out to find out the difference between ordinary noise and excess noise, as well as the limiting levels. The studied excess noise components included amplitude modulation, impulse noise and tonal noise.

In the current study the computational tools to evaluate all these features were developed and utilised. The amplitude modulation tools are founded on IOA AMWG proposal. It consists of 3 different approaches: Time Series Method, Fourier Analysis Method and Hybrid Reconstruction Method. IOA has published code for these methods. The methods need 100 ms LAeq data (Method 1) or 100 ms band-filtered data (Methods 2 and 3) as input. Our algorithms use original time signals as input. They give comparable results to the IOA program for Methods 2 and 3. For Method 1, results differ slightly. This is mainly because in IOA’s program the LA values for time constant S are calculated with an approximate formula of NT 112 based on LAeq value and LAS value of an earlier time step. When refining this formula by more terms in Taylor’s series, the results coincide with our results.

The developed tools are currently used to compute the excess features of the acquired time-domain wind turbine noise data. In an ongoing national wind turbine noise project WindSoMe continuous recording of 4 logging stations are automatically and remotely stored in a server. This big data is processed with these computation tools. The processed parameters are stored in a feature database. Additionally, the database contains meteorological and on-line questionnaire information. This facilitates the pin-pointing of the interesting wind turbine noise phenomena. It also makes it possible to better understand the causes of specific noise conditions and ways to improve the situation.

Low-frequency noise incl. infrasound from wind turbines and other sources

Presenting Author: Steffen Pankoke, Managing Director, Wölfel Wind Systems GmbH + Co. KG

Abstract: In recent years, the issue of low-frequency noise – especially infrasound – has aroused great interest not only among experts, but also among the general public. The reason for this is probably the discussion about the expansion of wind power. In the years 2013-15, LUBW Landesanstalt für Umwelt, Messungen und Naturschutz Baden-Württemberg and company Wölfel Engineering performed extensive measurements of low-frequency noise (incl. infrasound of 1 Hz and higher) in the immediate vicinity of six wind turbines, in urban and rural areas as well as in areas that are explicitly dominated by road traffic. The aim of the project was to collect comparable data about the occurrence of infrasound and low-frequency noise in the vicinity of wind turbines and other sources. The measurements on wind turbines with a capacity of 1.8 to 3.2 MW were performed simultaneously with different distances to the respective wind turbine. The infrasound emitted by wind turbines could be measured very well in the close vicinity of the turbines. Here, the sound intensity is below the human perception threshold. The large amount of data was documented in different evaluations (e.g. linear third-octave band levels, narrow-band spectra, G-rated overall sound pressure levels depending on wind speed or time of day). The measurement method and the main results are presented in this paper.

Wind turbine noise monitoring and clustering for automated noise analysis

Presenting Author: Petri Välisuo, Assistant professor, University of Vaasa

Abstract: We have constructed four wind turbine noise recording stations and installed them around a wind park to acquire time series signal of wind turbine noise for 12 months. The data is recorded at the sampling rate of 22500 Hz and the microphone bandwidth cover frequencies from 3 Hz to 20 kHz. The stations transfer the recorded data to the server in approximately 15 minutes after it has been recorded. The noise can be accessed from the server for listening and for automatic analysis. To be able to assess the noise contribution of the wind turbines, external intermitted noise sources, such as by passing cars, bird calls, aeroplanes and other similar sources were at first manually segmented by listening to a subset of the sound samples. Then an automatic clustering algorithm was applied to the rest of the data to label the clusters according to the manual segmentation.

Segmentation is a vital first step for wind turbine noise analysis to exclude the samples contaminated by other noise sources. Manual segmentation is impossible due to a large amount of data. The segmentation uses principal component analysis for dimensionality reduction and a mean-shift clustering algorithm to group the samples into clusters. The large amounts of noise data require special arrangements for applying the algorithms for all recorded samples. We have used a grid computing cluster to analyse the data which requires already two terabytes of disk space and is supposed to be extended to more than 10 terabytes within 12 months. A limited amount of sound data analysis made this far suggests that the wind turbine is not apparently a dominant noise source in the neighbourhood and it may not be an exceptional source of infrasounds.

Automatic detection of wind noise on recordings of wind turbine noise for the purpose of maximising accuracy of amplitude modulation ratings

Presenting Author: Sabine von Hünerbein, Senior lecturer, University of Salfort

Abstract: Microphone wind noise can corrupt outdoor measurements and recordings. It is a particular problem for wind turbine measurements because these cannot be carried out when the wind speed is low. Wind shields can be used, but often the sound level from the turbine is low and even the most efficient shields may not provide sufficient attenuation of the microphone wind noise.

This study starts by quantifying the effect that microphone wind noise has on the accuracy of two commonly used Amplitude Modulation (AM) metrics. A wind noise simulator and synthesised wind turbine sounds based on real measurements are used. The simulations show that even relatively low wind speeds of 2.5 m/s errors of over 4 dBA can result. Microphone wind noise is intermittent, and consequently one solution is to analyse only uncorrupted parts of the recordings. This paper tests whether a single-ended wind noise detection algorithm can automatically find uncorrupted sections of the recording, and so recover the true AM metrics. Tests showed that doing this can reduce the error to ±2 dBA and ±0.5 dBA for the time and modulation-frequency domain AM metrics respectively. The paper goes on to validate the simulation approach by applying the automatic detection to near field recordings from various adjacent microphones in combination with high quality meteorological mast measurements within 40m of the microphones and wind turbines.

Session 2 – Wind farm design & siting

Assessment of noise prediction methods for long range sound propagation of wind turbines over land with focus on German guidelines

Presenting Author: Lukas Mylonas, Expert Wind & Site Assessment, WKN AG

Abstract: Noise estimations for wind energy projects are receiving a close review in Germany at the moment. The ISO 9613-2 standard – initially developed for 30 m high industrial sources – is being scrutinised for its applicability to accurately estimate noise immissions from high emitting sources such as wind turbines.

In this study different models for estimating onshore wind turbine noise are assessed. Among others the new draft version of the German method (“Hinweise zum Schallimmissionsschutz bei Windenergieanlagen”) is evaluated and compared with international prediction methods like the NORD2000, the Danish model and the ISO 9613-2. In addition a partial differential equation (PDE) based on the Crank Nicholson scheme is used as a reference model. Sound propagation for different measured onshore wind speed profiles is simulated using the PDE model and results are compared to the aforementioned engineering methods.

The results of the study highlight the weakness of some methods in taking into account important influence factors for outdoor sound propagation, such as refraction and ground reflection. On the other hand, implementation of other important influence factors like diffusion and ground diffraction in more complex methods are not trivial.

Furthermore modern wind turbines are high emitting sources with hub heights of more than 100m while the ISO 9613-2 was originally developed for industrial complexes of 30 m height. In addition the new proposed draft of the German method seems overly conservative due to the fact that it considers the ground surface to be totally reflective. The reason for taking this approach is mainly due to the assumption that the ground attenuation methods described in the ISO 9613-2 cannot adequately estimate the ground effect for high emitting sources.

In order to prevent more restrictive estimation methods being imposed on the wind industry more reliable noise standards adapted to modern wind turbines need to be developed that have the flexibility to be coupled with more complex methods.

Impact of various national codes on wind farm design

Presenting Author: Thomas Sørensen, Senior wind energy consultant, EMD International A/S

Abstract: Noise impact from wind turbines on dwellings is one of the primary constraints on wind farm design when operating in populated areas. Though noise is a physical property, the constraint is usually defined by national codes and these differ from country to country.

There are differences in terms of:

• Noise limits – either absolute or relative to background
• Wind speeds to consider – single values or ranges
• Propagation models
• Validation though measurements and associated uncertainties

Each code has its own challenges in terms of data requirements, associated costs and limitations and it is not always apparent which codes are more restrictive than others.

This study analyses the effect of the different national codes in countries including Germany, the Netherlands, the UK, Denmark, Norway, Sweden and Finland on a virtual wind farm layout on a generic, but realistic site. Wind farm size and production output are used as a measure of the constraints, but the analysis also highlights the particular challenges posed by each code. In this way the consequences of the otherwise incomparable noise codes can be evaluated on equal terms.

Each code has advantages and drawbacks and occasional obscurities and as a balance is sought between protection of amenity, safety and convenience.

Session 3 – Wind Turbine Design

High spatial and temporal resolution Wind Turbine Noise directivity characteristics measured with a very large aperture microphone array

Presenting Author: Stuart Bradley, Professor, University of Auckland

Abstract: A 40 m diameter microphone array was used to acoustically image the noise source characteristics across the entire diameter of a turbine at a spatial resolution of 1 m and at 1/3 octave resolution. Measurements were made on the 42 low-noise microphones synchronously with video of the turbine. This allows simultaneous definition of the spatial, temporal, and spectral properties of the generated sound. Very high quality, fast, meteorological profile data was available from nearby 80 m masts and from the turbine nacelle, giving wind speed, wind direction, and turbulence data. A tonal speaker source was mounted at the base of the turbine tower, for determining the spatial characteristics of coherence, and for compensating for local wind variations.

An experiment was also run recording the sound from a continuous tone speaker mounted near the tip of a turbine blade, allowing testing of signal processing to correct for the very substantial Doppler shift. High resolution image results are given as well as time-resolved and spectrally-resolved turbine noise directivity patterns.

These new measurements are near-field, so that propagation effects are essentially minimized, with the aim of providing source characterization. Comparisons are given with existing aero-acoustic models and statistically significant differences critically examined.

Leading edge modifications (protuberances) on rotor blades which reduce blade noise and fatigue loads

Presenting Author: Achim Fischer, General manager, CFD+engineering GmbH

Abstract: Leading edge modifications (protuberances) on rotor blades which reduce blade noise and fatigue loads are presented. The physical effect of such protuberances is that they produce secondary vortices that travel over the upper side of the airfoil. Like that they do not only re-energize the boundary layer, they also help to devide the trailing edge stall into smaller units and therefore reduce the blade´s noise production.

Recent scientific measurements by K. L. Hansen et al. and C. Polacsek et al., had demonstrated the positive effects of protuberances for standard aircraft airfoils. The work presented here was developping a wind power airfoil with such protuberances to be used in a real windpower blade application at a later stage.

Acoustic and aerodynamic wind tunnel tests carried out at the DLR windtunnel on said windpower airfoil in several configurations are presented and the effect on sound generation is demonstrated.

Low-Noise Technologies for Wind Turbine Blades

Presenting Author: Michaela Herr, Acoustic Engineering, German Aerospace Center (DLR)

Abstract: The BMWi-funded wind energy project BELARWEA aims at the development and validation of improved methods to support the design of both efficient and low-noise wind turbine rotors. Aeroacoustically driven 2D profile design, 3D winglet design and 2D/3D CFD and CAA analysis are supplemented by the transfer of passive noise reduction technologies from aerospace applications to wind turbine blades. Based on a down-scaled version of the open source NREL-5-MW reference rotor, a noise reduction of at least 3 dB at a given rotor performance is targeted by a dedicated 3D redesign of the outer 20% of the rotor radius.
Experimental demonstration and tool validation shall be provided in systematic validation steps, i.e.
• at 2D blade sections in the AWB acoustic wind-tunnel of DLR and
• at 3D blade tips in the larger acoustic facility DNW-NWB, operated by the German-Dutch Wind-Tunnels Foundation.
The presentation will in its first part provide an overall project overview. In its second part results from the first set of AWB measurements will be summarized, yielding a detailed matrix of the relevant system parameters (i.e. aerodynamic performance vs. noise). Aeroacoustic predictions will be compared with the experimental results and transposed to full scale conditions. In addition, the noise reduction potential of selected trailing-edge add-ons will be evaluated at varying test velocities, angles of attack and boundary-layer transition regions.

ALARM: Research on wind turbine tonalities

Presentign Author: Fred Vanhollebeke, Technology Engineer, ZF Wind Power Antwerpen NV

Abstract: Although aero-acoustic noise is considered as the dominant source of wind turbine noise, mechanical noise, coming from gearbox or generator, could – especially when it contains audible tonal components – result in non-conformity to local noise regulations. This becomes more stringent when wind turbines are installed closer to urbanised areas. To reduce the risk of tonalities in prototyping or production phase, an international consortium active in wind turbine development – consisting of wind turbine OEM, component manufacturers and research institutions – started the European Eureka research project ALARM to advance the state-of-the-art in the field of wind turbine vibro-acoustic assessment. This project covered all aspects of mechanical wind turbine noise from gear excitation, mechanical transfer paths, vibration insulation up to acoustic radiation and transmission. All mentioned aspects have been analysed both from simulation side as well as from measurement side both on component level and on wind turbine level.

Intermediate project results have been reported in the EWEA wind turbine noise workshops 2012 and 2014. After successful conclusion in 2015 this presentation describes the main lessons ZF has learned from this research project. It will be shown how a combined approach of simulation and measurement has revealed valuable insights on the interaction of structural dynamics from different sub-systems in the wind turbine – drive train, support system, tower and blades. Several leverages have been identified to optimise overall vibro-acoustic behaviour of the turbine already in prototype phase. The presentation will conclude with an outlook on the remaining challenges in order to make this a successful approach in preventing wind turbine tonalities.

Mastering Tonalities with Active Vibration Control

Presenting Author: Steffen Pankoke, Managing director, Wölfel Wind Systems GmbH + Co. KG

Abstract: When considering wind turbines in relation to noise, tonal components are critical, since they cause a particular disturbance for the hearing impression. This fact is supported by the assignment of tonality surcharges in the assessment of noise emissions according to IEC 61400-11 and national counterparts. Despite careful design of the wind turbine, unwanted tonalities can still occur during operation. Their removal can be very complex, especially if a speed dependency of the tonalities is present.

One approach to mitigate emerging tonalities is the use of distributed active vibration absorbers. By means of appropriate control strategies, suitable positioning of absorbers and sensors, the entire speed range of the turbine can be addressed. The active absorbers of the study discussed here generate dynamic forces up to 5 kN each at a system mass of about 100 kg. The positioning of the absorbers requires the knowledge of the sound radiating components. This can be determined by structure-borne and airborne sound measurements, ideally together with finite-element-simulations of the system. With a structural dynamic model of the wind turbine first the structure-borne noise of potentially radiating components is calculated. By means of the transfer of structure-borne noise to an appropriate airborne noise model and subsequent extrapolation to the reference point the contributions of the individual components to the tonality level can be determined.

The next step is the integration of the active vibration absorber in the simulation model to determine the power requirements and the optimal placement. A comparison of the calculated sound level with and without absorbers allows a quantification of the achievable noise reduction. The active control approach has been developed to a series solution and has proven its efficiency in reducing tonalities with more than 800 active vibration absorbers in the field.

Session 4 – Human perception & guidelines

Recent developments in the rating and control of amplitude modulation in the UK

Presenting Author: Gavin Irvine, Director, Ion Acoustics Ltd

Abstract: A working group set up by the Institute of Acoustics (IOA) has developed a method for rating amplitude modulation in wind turbine noise. The working group comprised acoustic consultants, developers, academics and local authority representatives.

The method, following the work of other researchers, takes a Fourier transform of band-limited, time series data to determine the fundamental modulation frequency (which should be related to the blade passage frequency of the rotor) and the second & third harmonics. These components are then used to reconstruct a time series, which should relate only to wind turbine AM, with the influence of other sources minimised.

The modulation depth is then calculated from the reconstructed time series following the method of Tachibana et. al., i.e. subtracting the L95 of the time-series from the L5. Various other checks and calculations are made to determine a value for a 10-minute period which describes the amplitude modulation within that period. The working group excluded consideration of the subjective response to amplitude modulation and any penalty mechanisms which could be devised.

However, WSP UK Ltd. was commissioned by the UK Government Department of Energy and Climate Change (DECC) to undertake a review of research into the effects of, and the subjective response to Amplitude Modulation (AM), with a view to providing protection where it is justified within the planning regime. The paper will outline the IOA method and also describe the potential methods to control AM and the recommended method suggested to DECC, and how that condition may be written in accordance with UK Planning Policy.

Application of the UK IOA AMWG AM quantification method – case studies & worked examples

Presenting Author: Dave Coles, Senior Consultant, 24 Acoustics Ltd

Abstract: Following the work of the AM Working Group (AMWG) for the UK Institute of Acoustics (IOA), a method for the quantification of amplitude modulation from wind turbines has been proposed. The intention of this method is for a consistent and repeatable measure of the modulation depth characteristics of wind farm noise, where that measure has some meaning in regards to the psycho-acoustic response people experience. Examples of an amplitude modulation assessment using this method are provided.

Results are presented, discussing the analysis of noise measurements undertaken at residential receptor locations near wind farm sites. Some of the issues involved are discussed, and several worked examples are detailed. The various tools that enable a practitioner to undertake such an assessment are discussed, along with the pitfalls that may need to be kept in mind.