Multiple leading edge vortices of unexpected strength in freely flying hawkmoth

Composite image of a representative vector field, color coded by vorticity, showing the complex leading edge vortex above the wing on top of a photo of a Hummingbird hawkmoth (Macroglossum stellatarum).

The first study of the flow above the wings of a freely flying insect, showing the structure of the lift boosting leading edge vortex, is published today by the Animal Flight Lab in Scientific Reports. The leading edge vortex is generally seen as a stable vortex, attached to the top surface of the wing, but this new study finds it to have a complex structure. At the inner wing the vortex has a single core, but mid wing and outwards the vortex is highly variable with multiple simultaneous cores. The highly variable flow may affect the aerodynamic control of the moth. In addition to the high complexity, the circulation of the vortex on the outer part of the wing is higher than the circulation measured in the wake behind the animal. This implies that the vortex accounts for the entire lift production at the outer wing and is in fact stronger than is necessary to generate the required lift force, which suggests a high aerodynamic cost of flight in the moths. These new findings will serve as a baseline comparison for past and future studies of the aerodynamics of insect flight based on tethered animals and mechanical flappers.

/Christoffer Johansson Westheim