C.F. e P. IVA WIND TURBINE GENERATOR SYSTEM ACOUSTIC NOISE TEST REPORT FOR THE WIND TURBINE REVISION 1.1

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1 studio associato Alfinito Nencini La Russa PISA Via Santa Maria, 19 C.F. e P. IVA info@studioanl.it fax: WIND TURBINE GENERATOR SYSTEM ACOUSTIC NOISE TEST REPORT FOR THE ARIA LIBELLULA WIND TURBINE REVISION 1.1 Studio Associato Alfinito-Nencini-La Russa Dott. Luca Nencini Fisico specialista Tecnico Competente in Acustica 349/

2 1 TEST OBJECTIVE The objective of this test is to give an estimate of the noise emission of the Libellula wind turbine. This report documents the measurements techniques, equipment, analisys procedures and results for apparent sound power level and dependance on wind speed. 2 WIND TURBINE GENERAL DATA Table 1. Turbine data GENERAL DATA Make Model ARIA SRL Serial Number Rotation Axis Orientation Number of blades 2 Rotor diameter (m) 18 Hub Height (m) 24 PERFORMANCE Rated electrical power (kw) Rated wind speed (m/s) Cut in wind speed (m/s) Cut out wind speed (m/s) ROTOR Libellula 55kW Horizontal Upwind 55kW 11m/s 3m/s 25m/s Swept area (m2) 254 Rotational speed (rpm) 0 to 90 Tilt angle (degrees) 7 Blade pitch angle 6,8 Direction of rotation Clockwise Overspeed control/protection Passive pitch regulation Power regulation (active/passive) Active _N284_test report1.1.doc 2

3 3 TEST SITE The Libellula turbine was located at approximately 700 meters from Campiglia Marittima (LI), Tuscany, Italy. The test site is located at an approximate elevation of 320 m above sea level. N Via Firenze Via Aurelia Turbine Figure 1: Test location Wind transducer n.1 Measurement point _N284_test report1.1.doc 3

4 Figure 2: Aerial photo of test location _N284_test report1.1.doc 4

5 Figure 3: Test turbine _N284_test report1.1.doc 5

6 4 TEST SETUP 2.1 Wind transducers position The transducer (n. 1) used for detection of wind direction was located 50 meters from the test turbine, at 6 meters height. This was the only possible choice for positioning the anemometer, due to the geomorphology of test site and wind direction coming from NNW. About 8 meters high trees were 15 meters from the anemometer, covering the direction 50º N to 140º N. Wind speed was detected and logged by anemometer (n.2) at the top of the turbine s tower at 24 meters and was corrected by an empirical factor to take in to account rotor blades induced turbulences. 2.2 Microphone position Microphone was located 29 meters from the centre of the tower. It was mounted at the centre on a flat hard circular board pointing towards the wind turbine to reduce the wind noise generated at the microphone and to minimise the influence of ground. The board had a diameter of 1,0 m and was made of plywood with a thickness of 15,0 mm. The angle between the plane of the microphone board and the line from the microphone to the rotor centre was 42 degrees. Preferred values of the above mentioned distance and angle would be respectively 33 meters and between 25 and 40 degrees, but the chosen values were the only possible ones due to the geomorphology of test site. 2.3 Measurement procedure Acoustical and wind data were acquired and recorded for 41 hours consecutively, starting from 00:00 of 11/05/11. Wind direction and speed from both anemometers and sound level were averaged over a minute. Data loggers were time-synchronized. Wind direction was observed from transducer n.1 to ensure that measurement locations were kept within 15 of nacelle azimuth positions with respect to upwind. The complete sound measurement system was calibrated immediately before and after the measurement session with acoustic calibrator _N284_test report1.1.doc 6

7 5 TEST EQUIPMENT Table 2 shows the list of equipment used for the test: Table 2. Turbine data INSTRUMENT MANUFACTURER MODEL SERIAL NUMBER Microphone 01dB MCE Preamplifier 01dB PRE 21S Datalogger 01dB Solo Calibrator 01dB Cal _N284_test report1.1.doc 7

8 6 ANALISYS METHOD 6.1 Data selection Acquired data were selected, excluding particular condition listed below: Wind direction outside of allowable range Test equipment failure Wind speed below cut-in Interference from unwanted noise sources 6.2 Wind speed correction The wind speeds measured is corrected to the wind speed Vs at reference conditions by assuming wind profiles in the following equation: Where: z 0ref is the reference roughness length of 0.05 m z 0 is the roughness length H is the rotor centre height z ref is the reference height, 10 m z is the anemometer height Vz is the wind speed measured by the anemometer _N284_test report1.1.doc 8

9 6.3 Background noise Because residual sound pressure levels at different wind speeds were estimated to be always at least 15 db(a) below wind turbine noise level, no correction for background noise have been applied. 6.4 Sound power level calculation The apparent sound power level L WA,k from the sound pressure level L Aeq,k at the integer wind speeds at the reference position as follows: L WA, K where: L Aqe, k 4 R 6 10log S R 1 is the slant distance in meters from the rotor centre to the microphone S 0 is a reference area of S 0 = 1 m 2 The 6 db constant in equation above accounts for the approximate pressure doubling that occurs for the sound level measurements on a ground board _N284_test report1.1.doc 9

10 7 RESULTS Figure 4 shows the data used for analysis and linear regression, corrected by 6 db(a) due to reflecting board, using the measured standardized wind speed. Each point represent a single noise measurement averaged over one minute. Figure 4: Polinomial regression of measured levels Data were interpolated by second order regression form Y= a + b 1 x.+ b 1 x 2 Table below shows obtained coefficients. Table 3. Fit coefficients VALUE ERROR a b c _N284_test report1.1.doc 10

11 8 CONCLUSIONS The sound power level Lw of Libellula wind turbine has been estimated by in situ measurements. Resulting values of Lw at integer normalized wind speed are listed in the table below. Pisa, 16/05/2011 Table 4. Sound power level at different normalized wind speed Normalized Wind Speed at 10 meters height m/s Lw db(a) Approved By Dott.Luca Nencini _N284_test report1.1.doc 11

12 studio associato Alfinito Nencini La Russa PISA Via Santa Maria, 19 C.F. e P. IVA l.nencini@studioanl.it fax: WIND TURBINE GENERATOR SYSTEM SOUND PRESSURE LEVELS OF ARIA LIBELLULA WIND TURBINE

13 The Sound Pressure Level L p of the Libellula wind turbine has been estimated at various distances for different wind speeds using spherical propagation model and L W values calculated in noise test report _N284_test report1.1. According to statement n. 14 of ETSU-R-97, an estimate of L A90,10min can be obtained subtracting a value of 2.0 db(a) from L Aeq. So the distance at which occur an L A90,10min of 35 db(a) can be calculated for each wind speed as reported in the last column 10. Wind speed at 10 meters m/s Wind speed at rotor m/s Lw in db(a) Lp in db(a) at distances (m) db(a) L A90,10min distance m First column shows normalized wind speed at 10 meters Second column shows wind speed at rotor using logarithmic wind profile Third column shows sound power level of wind turbine Columns 4-9 shows Sound Pressure Level calculated at various distances _N284_distances_.doc 2

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