so they can fly in silence

Using computer simulations, researchers are studying the mechanisms that allow owls to fly silently

Owls are fascinating creatures that can fly silently through the quietest places. Their wings make no sound when flying, allowing them to accurately locate their prey without being detected thanks to their exceptional hearing. This unique ability depends on many factors and has long been a hot research topic.

Studies have found a connection between the ability to fly silently and the presence of microfringes on owls’ wings. These trailing edge (TE) stripes play a crucial role in suppressing noise caused by the air movement caused by wing beats.

Studying these peripheral areas could lead to the development of promising methods for Reduce the noise caused by turbomachinery, for example the rotors of electric wind turbines or aircraft engines. Although many studies have examined these fringes using flat plates and airfoils, their exact mechanisms and effects on the feather interactions and distinct wing properties of real owl wings are still unknown.

Owl wings with fringes

The micro fringes on the owl wings effectively suppress noise while ensuring that the aerodynamic performance of the wings remains comparable to that of a wing without fringes. Photo: Hao Liu, University of Chiba

To unlock the secrets of silent owl wings, Professor Hao Liu and his colleagues, including Dr. Jaixin Rong from the College of Engineering and Dr. Yajun Jiang and Dr. Masashi Murakami from the College of Engineering, of Science at the University of Chiba (Japan) studied how TE fringes affect both the sound and aerodynamic performance of owl wings.

When asked about the motivation for his study, Professor Liu says: “Despite the efforts of many researchers, the exact question of how owls achieve silent flight remains an open question.” “If we examine the exact role of TE stripes in their silent flight “Understanding this, we can use them in the development of practical, low-noise fluid machines.” Their results were published on November 17, 2023 in the journal Bioinspiration & Biomimetics.

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To understand how owl wings work, the team built two three-dimensional models of an eagle owl wing – one with and one without TE fringes – with all of its geometric features. Using these models, they performed fluid flow simulations that combined large vortex simulation methods and the Ffowcs-Williams-Hawkings analogy. The simulations were carried out at the approach speed of an eagle owl.

Simulations showed that the TE fringes reduced the noise level of the owl’s wings, particularly at high angles of attack, and maintained aerodynamic performance comparable to that of the owl’s wings without the fringes. The team identified two complementary mechanisms by which TE strips affect airflow. First, fringes reduce airflow fluctuations by breaking up trailing edge vortices. Second, they reduce the flow interactions between the feathers at the wing tips and thereby suppress vortex shedding at the wing tips. Synergistically, these mechanisms enhance the effect of TE strips and improve both downforce generation and noise reduction.

Emphasizing the importance of these results, Professor Liu explains: “Our results demonstrate the effect of the complex interactions between TE strips and various wing properties, highlighting the validity of using these strips to reduce noise in practical applications such as drones, wind turbines, propellers, and even flying ones Cars.

Overall, this study deepens our understanding of the role of TE fringes in silent flight of owls and could inspire biomimetic designs that could lead to the development of low-noise fluid machines.

REFERENCE

Trailing edge edges enable robust aerodynamic force generation and noise cancellation in an owl wing model

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