Poster presentations

Abstracts

Topic 1: Real-world noise measurements

PO.001 –Measurement  system for wireless monitoring of wind turbine noise in the audible and infrasound range

Presenting author: Tomasz Malec, KFB Polska Sp. z o. o.

Abstract: 

The poster presents a wireless, multi-channel and multi-position monitoring system of wind turbine noise with the function of monitoring weather conditions. The system allows the acquisition of complete data (full band spectrum with sampling frequency 51,2 kHz). The signal is transmitted to the base station wirelessly. Measurements can be carried out in four points at the same time with the distance from the base station up to 300m. Signal is a full record audio across spectrum from 1 Hz to 20 kHz. This makes it possible to carry out any analysis of the measured signals. The system allows to measure weather conditions synchronously. It runs on its own power supply, which enables continuous measurement up to 12 hours (optional over 24h). The system meets the requirements of IEC 61400-11. The system was created to monitor infrasound noise of wind turbines for different weather conditions. Poster shows the structure of the system, and examples of the results of research and analysis that can be performed.

PO.002 – Wind turbine excess noise big data analysis

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

Co-author(s): Jari Kataja, Heikki Isomoisio, Seppo Uosukainen, 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.

Topic 2: Wind farm siting and operations

PO.003 – Sensitivities of wind farm noise propagation to the input parameters

Presenting author: Emre Barlas, PhD Student, DTU Wind Energy

Co-author(s): Wei Jun Zhu, Wen Zhong Shen

Abstract: In this study we investigate the sensitivities of wind farm noise propagation to the input parameters i.e. background flow field, terrain undulation, impedance changes and source height. The Parabolic Equation (PE) method is used as the noise propagation model and the flow field is obtained from a flow solver that solves Reynolds Averaged Navier Stokes equations with the actuator disk model for representation of the turbines. Both steady and unsteady approaches are employed using either a single steady point source or a moving source with the rotor. The investigation is carried out by starting with a range independent flow field along the propagation path and neglecting the terrain undulation and source height variation. Afterwards the complexity is increased gradually where all the known parameters are fed into the PE model. The investigation is carried out for different receiver locations. The initial results show that the terrain effect is one of the most important parameters as it results in complete different refraction patterns in comparison to flat terrain. With a more comprehensive study it is aimed to underline the important factors that one should pay attention during a wind farm development process with respect to noise issues.

Topic 3: Wind turbine design

PO.005 – Leading edge modifications (protuberances) on rotor blades which reduce blade noise and fatigue loads

Presenting author: Achim Fischer, General Manager, CFD+engineering GmbH

Co-author(s): Stefan Kleinhansl, ADC

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.
The benefit of the proposed new approach is that a true representation of the asset’s energy production can be obtained without biases introduced due to poor turbine availability. The new method requires detailed understanding and more intensive data analysis; however it is considered that this yields benefit for both parties (buyer and seller of energy) as more accurate Deemed Energy Payments will result.

PO.004 – Optimising site noise constraints with an automated algorithm

Presenting author: Matthew Cand, Associate Engineer, Hoare Lea Acoustics

Co-author(s): Mathilde Boissier

Abstract: Environmental noise frequently represents one of the most controversial and restrictive aspects of proposed wind energy developments. Wind farm noise assessments require a careful balance to be struck between utilising the full available generating potential of a site and controlling the risks of excess noise generation. As developable land suitable for wind farms becomes less and less available, more challenging sites are having to be selected.
At the same time, improvements in turbine technology have meant that a variety of noise-controlled modes are available for modern variable speed machines. This allows noise reductions to be applied, in the required conditions, at a marginal but sometimes appreciable energy cost.
Historically, the operational strategy for a wind farm would be determined manually such that the consented noise limits would not be exceeded at neighbouring noise-sensitive locations, based on predictive models which now increasingly take into account not only wind speeds but also wind direction.
But there can be different strategies that result in compliance, and it is sometimes difficult to determine the optimal one to take. Which is better: fewer turbines operating without any constraint or a greater number with some operational constraint?
The authors have developed a new approach to this challenge, by considering not just noise but also the associated energy generation of each turbine, and determining a solution using novel iterative optimisation techniques. This method considers all locations and turbines together and systematically, which is not possible manually in practice, and explores the large number of theoretical possibilities in an optimal way.
Operational strategies developed using this approach have in simple cases shown improvements in the potential energy generation of a wind farm of as much as 2% over a standard approach, which can be significant over the life of a project.

PO.006 – Mastering tonalities with active vibration control

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

Co-author(s): Jürgen Engelhardt, Sebastian Katz, 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.

Topic 4: Guidelines and human perception of noise

PO.007 – Application of the UK IOA AMWG AM quantification method – case studies & worked exaples

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

Co-author(s): Matthew Cand, Hoare Lea, Tom Levet (Hayes McKenzie Partnership 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.