Flying snakes — how do they do it?

Don't let their wingless bodies fool you - some snakes can glide as far as 100 feet through the air, jumping off tree branches and rotating their ribs to flatten their bodies and move from side to side. New research from a George Washington University professor investigates the workings behind the flight and whether they can be applied to mechanical issues.

Image courtesy Jake Socha

Lorena Barba, associate professor of mechanical and aerospace engineering in the GW School of Engineering and Applied Science, and her team, including Anush Krishnan, a senior research assistant at GW and Ph.D. student at Boston University, built a computer model using one of the latest technologies in computing, known as graphic processing units (GPUs), and applied computational fluid dynamics to study the aerodynamics of flying snakes.

The research, titled Lift and Wakes of Flying Snakes and conducted at BU, appears March 4 in the journal Physics of Fluids. This work is the first to study the lift of a snake's cross-section computationally.

''With simulation, you can really see the fine details of what is happening in the air as it moves around the object,'' Dr. Barba said. ''We decided it would be revealing to use this tool to find out, first of all, if we could observe the same feature of lift, and if so, if we would we be able to interrogate the flow by getting detailed quantities and visualizing it.''

Three species of snakes in the genus Chrysopelea are known to glide, and one, Chrysopelea paradisi, has even been seen turning mid-air. At least 30 independent animal lineages have evolved gliding flight, but the flying snake is the only glider without appendages, using a similar mode of locomotion to navigate the earth, water and air.

Dr. Barba's collaborator, Jake Socha, an assistant professor at Virginia Tech, has been studying and filming the movement of flying snakes for years by launching them from cranes in their natural habitats. His team also built physical models with tubing, testing them in a wind tunnel. The group expected the aerodynamic lift of the snake to increase with the angle of attack (the angle between the profile and the trajectory of flight) and then to drop suddenly after a stall. But what they actually measured was lift that increased at attack angles up to 30 degrees, a sharp boost at an angle of 35 degrees, then a gentle decrease. This suggested snakes use a mechanism called ''lift enhancement'' to get an extra boost, Dr. Barba said.

With that information, Dr. Barba and her team decided to model a 2-D cross-section of the snake body using GPU-accelerated computational fluid dynamics simulations. The researchers observed the same lift enhancement and were able to measure and visualize the details of air rotation and air pressure. The computer model acts as a ''virtual microscope'' for fluid mechanics, allowing the researchers to zoom in very close to the body to understand how the air is swirling around the snake.