With Global Warming becoming a greater concern each year, countries around the world turn to renewable power sources. Scientists believe that using green and sustainable power could decrease the effects of climate change.
One alternate way of producing power is with the help of wind turbines. It’s popular, because it’s the most cost-effective renewable power source out there, and its operation creates no greenhouse gases, nor any pollution. But of course, wind power has some negative side effects.
One important side effect is noise pollution, as it could affect residents of nearby cities.
Noise pollution can cause physiological and psychological problems. In an office environment, for example, it can negatively affect productivity, concentration and can also increase stress. Many other factors can make a workplace difficult to work in, you can read more about surviving in such an environment.
But What is Noise Pollution and How Does a Wind Turbine Create it?
Noise pollution is any sound or noise that is louder than the usual background noise you hear. In case of wind turbines, it has two different kinds: mechanical and aerodynamical. Mechanical noise is created by the friction between two components of the machinery, and vibrations induced by the rotating components. The generator, fans, and hydraulic systems all contribute to it.
Aerodynamical noise is more complex and is the dominant source of noise from a turbine. It comes from the motion of the air around the blades. It’s proportional to the speed of the blades.
Wind turbine parks were also found to create infrasound. Infrasound or low-frequency sound is noise below the lower limit of audibility. Although humans can not hear it, it can still have a serious health effect. Studies conducted in the matter found that the infrasound produced is below the natural background infrasound, meaning it has no harmful consequences.
Let’s look at a few examples of noise pollution and how loud they are. A busy office environment is around 60 dB, a loud concert is 100 dB, a commercial airline flying above resident areas (near airports) is about 200 dB. A wind turbine produces approximately 100 dB of noise, and it drastically decreases as the distance increases.
250 meters away from the turbine, the noise is at 50 dB, but from 2 kilometers away it’s only about 20 dB. Depending on which way the wind is blowing, this noise rate can decrease by 10 dB.
Noise Reduction Strategies
In the case of mechanical noises, there are different ways to minimize unwanted vibrations. Vibration control is implemented in more and more new designs. They include the use of sound-isolating materials, insulation, and closing the holes in the nacelles which would decrease the sound transmitted to the air.
There are several adaptive noise reduction approaches for aerodynamic noise, including varying the speed of rotation of the blades. Since an increase in rotational speed will also lead to increased noise production, lowering the rotational speed will lead to decreased sound.
However, the rotational speed decrease reduces power output, and therefore should only be implemented within a certain range of wind velocities, since high winds also have the added benefit of masking the sound of the wind turbine with the sound of the wind itself.
The pitch angle of the wind turbine blades also has an important role in noise production. An increase in pitch angle will lead to a reduction in the angle of attack. If the pitch angle is reduced, a thinner boundary layer results on the suction side, which is considered the strongest source of noise production.
The major drawback to this adaptive noise control method is the corresponding reduction of power output since the angle of attack is decreased. Despite the loss in power, the main advantage of wind turbines with optimized operating conditions is that the acoustically affected areas are much smaller, allowing more wind turbines to be built in a wind park.