Future flying robots could be inspired by the aerodynamics of gliding snakes

The researchers used data from high-speed footage of flying snakes to construct a computational model to explain how the undulations provide lift. Crucial to this model was the snake's body's cross-sectional shape, which resembles an extended frisbee or flying disc.

To comprehend this significant body shape, one must first appreciate what gives a frisbee its exceptional ability to fly. That is, when a frisbee is spun, it increases the air pressure underneath it and creates suction on top, which lifts the disc into the air.

A gliding snake pretty much does the same thing. To help create the same type of pressure differential across its body, the snake undulates from side to side, producing low pressure above its back and high pressure beneath its belly. The result? An elevated snake that can float through the air.

Less means more

The scientists looked at several characteristics to discover which were crucial for producing glides, such as the snake's frequency of undulations and the angle of attack it makes with the incoming airflow. 

They found that flying snakes normally undulate at a frequency of 1-2 times per second in their natural habitat. Surprisingly, they also discovered that faster undulation reduces aerodynamic efficiency.

"The general trend we see is that a frequency increase leads to an instability in the vortex structure, causing some vortex tubes to spin. The spinning vortex tubes tend to detach from the surface, leading to a decrease in lift," stated author Haibo Dong of the University of Virginia in a press release.

Significance of 'LEVs'

Additionally, "The snake's horizontal undulation creates a series of major vortex structures, including leading-edge vortices, LEV, and trailing-edge vortices, TEV," added Dong.

"The formation and development of the LEV on the dorsal, or back, surface of the snake body plays an important role in producing lift," he explained.

The researchers declared that these LEVs initially form close to the head before traveling back along the body.

They also shared that the LEVs stay in place for extended periods before being shed at the snake's body curves. Significantly, comprehension of the lift process requires an understanding of these curves, which are formed during the undulation.

The researchers hope their discoveries may eventually help designers create snake robots with this flying ability more effectively. What do you envision these snake-like flying bots being useful for in the future?

Study abstract:

This paper numerically studies the flow dynamics of aerial undulation of a snake-like model, which is adapted from the kinematics of the flying snake (Chrysopelea) undergoing a gliding process. The model applies aerial undulation periodically in a horizontal plane where a range of angle of attack (AOA) is assigned to model the real gliding motion. The flow is simulated using an immersed-boundary-method-based incompressible flow solver. Local Mesh Refinement (LMR) mesh blocks are implemented to ensure the grid resolutions around the moving body. Results show that the undulating body produces the maximum lift at 45{degree sign} of AOA. Vortex dynamics analysis has revealed a series of vortex structures including leading-edge vortices (LEV), trailing edge vortices (TEV), and tip vortices (TV) around the body. Changes in other key parameters including the undulation frequency and Reynolds number are also found to affect the aerodynamics of the studied snake-like model, where increasing of undulation frequency enhances vortex steadiness and increasing of Reynolds number enhances lift production due to the strengthened LEVs. The findings of this study are expected to serve as a basis for investigating more comprehensive snake-like undulation locomotion patterns during gliding from the perspective of aerodynamics.