  Flying snakes use a unique method of aerial locomotion: they jump from tree
branches, flatten their bodies and undulate through the air to produce a glide.
The shape of their body cross-section during the glide plays an important role
in generating lift. This paper presents a computational investigation of the
aerodynamics of the cross-sectional shape. Two-dimensional simulations of
incompressible flow past the anatomically correct cross-section of the species
Chrysopelea paradisi show that a significant enhancement in lift appears at a
35-degrees angle of attack, above Reynolds numbers 2000. Previous experiments
on physical models also obtained an increased lift, at the same angle of
attack. The flow is inherently three-dimensional in physical experiments, due
to fluid instabilities, and it is thus intriguing that the enhanced lift also
appears in the two-dimensional simulations. The simulations point to the lift
enhancement arising from the early separation of the boundary layer on the
dorsal surface of the snake profile, without stall. The separated shear layer
rolls up and interacts with secondary vorticity in the near-wake, inducing the
primary vortex to remain closer to the body and thus cause enhanced suction,
resulting in higher lift.
