Chinese engineers have made a wind turbine generator adapted for low wind speeds. It is based on the Bernoulli effect, which made it possible to stabilize the vibrations of two flexible strips in the wind. As a result, the wind speed required for efficient operation has dropped by almost half compared to other structures. The article was published in the journal Physical Science .
Triboelectric generators (or tribogenerators) are devices that generate current from friction in a manner similar to how wool is electrified. The source of movement for the triboelectric effect is not important, often the movement of the human body is used to recharge wearable electronics , and Korean scientists powered toys from the touch of children. If we talk about the use of wind energy, then at the moment the turbines have no competitors in terms of power, but it is impractical to build them for powering small autonomous devices. At the same time, a wind turbine generator smaller than the palm of your hand is able to power a weather sensor or other similar devices.
The performance of wind turbine generators can be increased by using a flutter. Usually this is the name for the disastrous effect for aircraft, which destroys the wings, but it manifests itself much more widely. Flexible bodies, like flags, leaves, sway in the wind. At certain ratios of the size of the panel and the wind speed, the flag and the air will enter into resonance, and the intensity of the oscillations will begin to increase sharply, which is convenient for generating energy.
Two decades ago, scientists experimentally found that the Bernoulli effect can further increase the amplitude of the oscillations. According to Bernoulli's law , as the flow rate of a liquid or gas increases, the static pressure drops. This is easy to be convinced of without special equipment: if you take two strips of paper, bring them parallel to each other at a distance of a couple of centimeters and blow between them, then they stick together. In the case when two flexible bodies are located at a close distance, the Bernoulli effect will intensify their flutter and synchronize the oscillation phases.
A team of scientists from Chongqing University and the Beijing Institute of Nanoenergy and Nanosystems led by Xin Chen has developed a wind turbine generator using the Bernoulli effect. Its key feature is two strips, eight centimeters long, consisting of layers of polyvinylidene fluoride and fluoroethylenepropylene, separated by a layer of silver. They were placed at a short distance parallel to each other and the wires were connected. In this form, the device can already generate electricity from the wind, but to extract maximum power, it was important to choose the right distance between the stripes. The fact is that at a minimum distance, they tend to oscillate synchronously, with zero phase shift. In this design, this is unprofitable: the generator is designed for the periodic contact of two elements. If the distance is too large, then synchronization will disappear altogether, and the oscillations will become chaotic. Therefore, by experience, engineers have found that it is best to install the strips at a distance of a quarter of their length. In this case, they oscillate in antiphase and stably touch.
The Tribogenerator based on the Bernoulli effect is good primarily because it is adapted to low wind speeds. Most of these devices reach their peak efficiency at flow rates in excess of ten meters per second, while the new sample performs well already at six. At wind speeds of four to fifteen meters per second, the generator produced 0.8 to 2.5 milliwatts, which is enough to power portable low-power devices such as LEDs or weather sensors.
Since electronic devices in the modern world are found at every turn, and there will be even more of them, engineers come up with new non-standard methods of generating current. For example, Boeing has patented an electric generator on the noise of aircraft, and a portable hydro turbine will help you charge your phone on a hike.