Wind turbines are significantly quieter with fan blades
The flapping of the wings is quick and silent, the mouse does not hear the owl coming. Suddenly the claws dig into the body and it’s game over. That makes a tasty supper – and not the last for today! The hunting success has many reasons, among others it is the wings that ensure that the owl is as good as inaudible during its flight. Researchers are now taking a closer look because they want to ensure that our wind turbines are as quiet as the nocturnal hunters.
Wind turbines are not welcomed in the neighborhood
Wind turbines are not welcome near residential areas. A weighty argument against peaceful coexistence with such a giant is the unpleasant noise level. Although modern wind turbines are already quieter than their predecessors, the owl is audibly ahead of them. Noise reduction is currently achieved with the help of an even fan structure in the wings. The symmetrical arrangement of the spikes is called serration. This reduces wind turbulence and reduces noise at the same time. The noise reduction is -3.68 decibels, after all.
»Reducing noise is still a challenge«
That’s where scientists from Xi’an Jiaotong University come in, who envisioned the barn owl’s fanned wings. These enable the bird of prey to fly almost silently. The researchers began to analyze different fan structures with regard to air flow and noise development and published their results in the journal Physics of Fluids. “Today, blade design has come a long way, but reducing noise is still a challenge,” says Xiaomin Liu, one of the study’s authors.
Sawtooth patterns prove effective
The trailing edge of the owl’s wings seems particularly important in this context: If the air flow is particularly even here, i.e. there is no turbulence, it remains largely still. Asymmetric structures prove particularly useful for this purpose, with prongs whose edges are sometimes curved, sometimes perfectly straight. This sawtooth pattern results in a noise reduction of 5.47 decibels. Although the number still seems quite small, it has relevant implications. Because: With an increase of just 10 decibels, many people perceive a doubling of the volume. The researchers are also working on further refinement of the serration, for example on the trailing edges of the wind turbine rotors.