Submitted to: Windpower
Publication Type: Proceedings
Publication Acceptance Date: July 10, 2006
Publication Date: August 25, 2006
Citation: Vick, B.D., Clark, R.N. 2006. Affect of new blades on noise reduction of small wind turbine water pumping systems. In: Proceedings of American Wind Energy Association. Windpower 2006 Conference and Exhibition, June 4-7, 2006, Pittsburgh, Pennsylvania. 2006 CDROM. Interpretive Summary: In the past few years there has literally been an explosion in the number of wind turbines installed in the world due to the low cost of wind generated electricity and the growing public concern over probable climate change resulting from the burning of fossil fuels. While the wind turbine boom has mainly been for utility scale size wind turbines with rotor diameters close or exceeding the size of football fields, the rising cost of utility bills and the decreasing cost of small wind turbines (rotor diameters 8 to 60 ft) has created a demand for these smaller size wind turbines. Since these smaller size wind turbines are usually located closer to people’s homes, their noise output is more important to those who are considering whether to purchase them. During normal operation the noise output from utility grid-tied wind turbines is less of a problem than stand-alone (not connected to the utility grid) wind turbines, but when the utility grid goes down the grid-tied wind turbine noise output will likely be higher than a stand-alone system. Most of the noise generated by a small wind turbine comes from the noise created by the fast turning blade rotor. Therefore, at the USDA-ARS laboratory near Bushland, TX, we measured the noise output on a 1 kW (10 ft rotor diameter) stand-alone wind turbine with 3 different blade designs and a 10 kW (23 ft rotor diameter) stand-alone wind turbine with 2 different blade designs. The noise output measured on both wind turbines was less for the newer blade designs. However, the noise from both small wind turbines was still judged to be annoying for most people when the wind speed exceeded 25 mph even for the improved blade designs. Since the high noise usually occurs at a certain blade rotor rpm, our main conclusion was that the small wind turbine manufacturers should investigate other ways of not exceeding this critical rotor blade rpm rather than trying to make further changes in the blade design to try to reduce the noise output. Some ways of keeping the critical rotor blade rpm from being exceeded include adding an electrical dump load or making design changes which will result in the wind turbine turning out of the wind (referred to as furling) at a lower wind speed. This paper was important in that it recommended to small wind turbine manufacturers that in terms of noise reduction, it was more important for them to concentrate on ways to keep the wind turbine blade rotor from exceeding a certain rpm (either by applying an electrical dump load or decreasing the furling wind speed) rather than trying to make further changes in the wind turbine blade design. This strategy should ultimately lead to a more acceptable product for consumers of small wind turbines.
Technical Abstract: Acoustical noise data were collected on small wind turbines used for water pumping -- different blade designs were tested on each wind turbine. Three different blade designs were tested on 1 kW wind turbines and each successive blade design was shown to produce less noise with respect to rotor speed. All three blade designs; however, produced acoustical noise above 80 dB during part of their operation due to wind turbine blade fluttering which occurred when a specific rpm was exceeded for each blade design. Two radically different blade designs were tested on a 10 kW wind turbine. For the loaded condition (online) the average acoustical noise measured for both blade designs was within a few dB of each other (noise under 70dB), but for the unloaded condition the average acoustical noise measured for the newer blade design was 4 to 8 dB less. The acoustical noise for both blade designs of the 10 kW wind turbine usually ranged between 70 and 80 dB in the offline condition, but occasionally exceeded 80 dB. Binning the measured sound data in terms of rotor or tip speed instead of wind speed greatly reduced the scatter in the data and enabled better evaluation of the noise emission for the different blade designs. A recommendation for obtaining an acceptable noise emission from a small stand-alone wind turbine can be found in the conclusions.