Background noise maps

Transcription

1 Background noise maps WHY IT IS CONVENIENT TO CREATE BACKGROUND NOISE MAPS DURING PLANNING PHASE THROUGH CFD WIND MODELS Ing. Andrea Bartolazzi Ing. Simone Marletti Ing. Beatrice Pistoni Windsim User Meeting Tonsberg June 2015

2 Why are background noise useful What are background noise maps. Are they used? Background noise maps are not generated because it would be too expensive and for that cost meaningless. As a matter of facts no one in the industry does preliminary background noise maps. When would they be needed? At the beginning of the permission process. Otherwise at the end of the permission process, when people perform real background noise measurement in sensible points it is too late At that moment either : the developer can change the layout or he needs to control power in a way to reduce noise, losing production or the developer stops the noisy turbines

3 Noise oriented wind farm planning Noise is influenced by Main wind direction the local winds. If we are able to calculate local winds we can calculate part of the local noise Interesting site Wind resource In the planning phase distance from the receivers should be inversely proportional to background noise In this case the receivers are Receiver open to main wind equally distant from the windy zone, and the possible effect of Receiver protected from main wind the turbines is similar

4 Why it hard to produce background noise maps Wind related Vegetation Interaction with structures Other minor noises (Human activities are partly related with wind, they usually decrease when wind increases) Non wind related Cars Waters Animals Farming activities LWR10 = Noise parameter for wind related noise. The meaning of this parameter, as expressed here, is the noise that we would have at 10 m/s in absence of not wind related noise [db] LNWR =Noise parameter for non wind related noise [db] Wind related noise Non wind related noise

5 Typical noise results and constraints It makes sense to produce a background noise maps as soon as possible. Even if, as in this procedure, it is a map valid only for windy moments. Two moments: For low winds a slight decrease When the wind increases a linear or logarithmic curve Regulation says: 37 db (Italy) 32 db (France) In the night ambient noise can be max 3 db higher than background noise (over 40 db) Hence turbine noise should not exceed ambient noise

6 Procedure L WR10 = Noise parameter for wind related noise. The meaning of this parameter, as expressed here, is the noise that we would have at 10 m/s in absence of not wind related noise [db] CFD model DTM 50 meters / Min node 2 m height L NWR =Noise parameter for non wind related noise [db] Roughness Only one direction / North / Stable air Measurements on site (8 points for 3 weeks) L on 1 minute Aeq V on 1 2m wind V and Direction on 10 40, 60, 80m wind Rain

7 Background noise map Values are expressed in 7 6 Main wind direction db. Green/White are the most quiet, deep blue the loudest

8 Background noise map 3D Wind direction Background noise map as seen from south-west at 500 m altitude The receivers are the small black and white balls Values are expressed in db. Green/White are the most quiet, deep blue the loudest

9 Correlation between model and measurements Noise measured [db] Correlation between 10 m/s CFD vs. measures is poor. Better correlation between CFD@15m/ s and measure. It 2 indicates R =0,57 Measurements are 40% higher than model Noise calculated with CFD model [db]

10 R1 The cross + indicates the CFD model The cross X indicates the correlation

11 R2 The cross + indicates the CFD model The cross X indicates the correlation

12 R3 The cross + indicates the CFD model The cross X indicates the correlation

13 R4 The cross + indicates the CFD model The cross X indicates the correlation

14 R5 The cross + indicates the CFD model The cross X indicates the correlation

15 R6 The cross + indicates the CFD model The cross X indicates the correlation

16 R7 The cross + indicates the CFD model The cross X indicates the correlation

17 R8 The cross + indicates the CFD model The cross X indicates the correlation

18 Conclusions This results suggests that this method to produce background noise maps is not usable to predict correctly the background noise in every point since the differences between receivers in local vegetation and structures are too high. This has an influence on the parameter L that need eventually to be WR10 mapped or corrected point by point. On the other hand this approach can be useful in a preliminary stage as qualitative maps, and used to identify which receivers should be kept at higher distances. A second possible use of this kind of analysis is acquire information in order to extend the background noise campaign to sites that were not measured.

19 Next steps Some key points could be taken into account in order to deepen this approach: Identify if roughness map, which usually describe vegetation, influence the noise map and can help to indentify L WR10 The flow of wind at mast height is less affected by obstacles in the area. To improve the receiver noise model we could create a relationship between wind at mast and wind at the receiver with a wind modelling software Execute a map of total and differential noise once a turbine layout has been decided Turbine operating pattern. Every turbine has different wind L choice: the choice of the parameter L is fundamental. WR10 WR10 On what does it depend? Type of vegetation, Distance from vegetation, Local air stability