Using dragonfly wings to study the relationship between wavy wing structure and vortex movements

Scientists from Hiroshima University have undertaken a study of dragonfly wings to better understand the relationship between wavy wing structure and vortex movements. They found that wavy wings had greater lift than flat wings.

Their work was published in the journal Physical Exam Fluids on December 7, 2023.

Researchers set out to determine whether the undulation of a dragonfly’s wing is a secret ingredient for increasing lift. While previous research has largely focused on the constant flow around the wing during forward motion, the impact of the vortices generated by its undulating structure on lift has remained a mystery.

The wing surfaces of insects like dragonflies, cicadas, and bees are not flat like the wings of an airliner. Insect wings are made up of nerves and membranes, and their transverse shapes are made up of apices (nerves) and line segments (membranes). Shape geometry appears as a connection of objects in a V shape or other shapes.

Previous studies have shown that corrugated wings, with their ridges and grooves, have better aerodynamic performance than smooth wings at low Reynolds numbers. In aerodynamics, the Reynolds number is a quantity that helps predict the flow pattern of fluids.

Previous aerodynamic studies of wavy wings have contributed to applications in small flying robots, drones and wind turbines. Since insects possess low muscular strength, their wavy wings must somehow give them aerodynamic advantages. Yet scientists have not fully understood the mechanism at work due to the wings’ complex structure and flow characteristics.

The researchers used direct numerical calculations to analyze the flow around a two-dimensional wavy wing and compared the performance of the wavy wing to that of a flat wing. They focused their study on the period between the initial generation of the tip vortex and subsequent interactions before detachment.

They found that the undulating wing’s performance was best when the angle of attack, the angle at which the wind meets the wing, was greater than 30°.

The uneven structure of the wavy wing generates unstable lift due to complex flow structures and vortex motions. “We discovered a lifting mechanism powered by a unique airflow dance triggered by a distinct wavy structure. This can be a game-changer compared to the simple plate-wing scenario,” said Yusuke Fujita, a doctoral student. student at the Graduate School of Integrated Sciences for Life, Hiroshima University.

The researchers constructed a two-dimensional model of an undulating wing using a real dragonfly wing. The pattern consisted of deeper wavy structures on the leading edge side and shallower or flatter structures on the trailing edge side.

Using their two-dimensional model, they further simplified the movement of the wings and focused on generating unstable lift through translation from rest. Translational motion, or gliding motion, is a primary component of wing motion, in addition to pitch and rotation. The researchers’ analysis expands understanding of the non-stationary mechanisms used by dragonflies during flight.

The research team considered two-dimensional models in their study. However, their work has focused on the aerodynamics of insect flight, where flow is typically three-dimensional.

“If these results are extended to a three-dimensional system, we hope to gain more practical knowledge for understanding insect flight and its applications in industry,” said Makoto Iima, professor at the Graduate School of Integrated Sciences for Life at Hiroshima University. .

For the future, researchers will focus their research on three-dimensional models. “We started things off with a model of a two-dimensional undulating wing in a sudden burst of motion. Now we’re embarking on the quest to explore increasing lift through a wider range of shapes and motions. “wings. Our ultimate goal is to create a new bio-inspired wing with high performance through our lift enhancement mechanism,” Fujita said.