Lift and wakes of flying snakes

TL;DR

This study uses computational simulations to analyze how the cross-sectional shape of flying snakes generates lift, revealing a lift enhancement at specific angles of attack due to boundary layer separation and vortex interactions.

Contribution

It provides the first detailed computational analysis of the aerodynamics of flying snake cross-sections, highlighting mechanisms behind lift enhancement at certain angles.

Findings

Lift peaks at 35° angle of attack at Reynolds numbers above 2000.

Flow separation occurs early on the dorsal surface without stall.

Enhanced lift is due to vortex interactions and boundary layer behavior.

Abstract

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.