Turbulence and Unsteady Flow

 

Effects of environmental turbulence on insect flight performance and movement patterns


Wild insects perform all of the flight behaviors essential to their survival while immersed in a complex, unpredictable aerial environment.  The extent to which turbulence affects insect flight performance is unknown, because most studies of flight biomechanics have been performed in controlled lab settings with simplified airflow, and turbulence in natural environments at biologically relevant size scales has not been characterized.  All natural aerial environments contain some degree of turbulence, a chaotic blend of swirling vortices spanning a wide range of sizes; in addition, solid objects in an insect’s habitat (e.g., flowers, trees, buildings) may produce flow that is unsteady but structured, shedding strong vortices of a particular size and temporal frequency.  The effects of these complex aerial environments on flying insects are likely to depend on the habitat type, the spatiotemporal niche that an insect inhabits, and the size and flight capacity of the insect itself. 


With the support of an NSF CAREER grant (IOS-1253677), we are addressing this large, unresolved question with three approaches: (1) characterizing the spatiotemporal characteristics of airflow in outdoor habitats, (2) reproducing natural aerial environments in a wind tunnel and testing insect flight performance, and (3) conducting tracking studies linked with environmental measurements to determine whether the aerial environment affects insect movement patterns at the landscape level.


We have constructed an anemometry system capable of measuring low-velocity, omnidirectional flows in natural habitats, and are beginning to characterize the spatial and temporal characteristics of airflow in a range of outdoor environments.  We have performed wind tunnel studies on bumblebees and tropical orchid bees, and find that both species experience large rolling instabilities when flying in unsteady flow, and that they adopt behavioral strategies that improve flight stability but likely increase the energetic cost of flight.  Orchid bees extend their hind legs far from their bodies to increase their moment of inertia when flying in turbulence, and bumblebees shift the position of their abdomen to help slow unintentional body rotations caused by aerial perturbations.  We are extending this work by examining how bees adjust their wing kinematics while flying in turbulence, and by testing whether passive wing flexibility improves flight stability in challenging aerial conditions. 


Finally, we are performing tracking studies on both bumblebees and orchid bees using RFID and optical technologies to determine whether unsteady flow in natural aerial environments affects when bees forage for resources, where they fly within the environment, or the quantity of nectar and pollen they are able to collect.  To understand how habitat alteration affects the aerial environment and movement of pollinators within these environments, we will perform studies in a variety of landscapes, including undisturbed forests, patchwork forest/agricultural landscapes, and urban/suburban areas.


Related Publications:

Ravi, S., Crall, J., Fisher, A. and Combes, S.A. (2013). Rolling with the

    flow: bumblebees flying in unsteady wakes.  J. Exp. Biol. 216:

    4299-4309.

Combes, S.A. and Dudley, R. (2009).  Turbulence-driven instabilities

    limit insect flight performance.  Proc. Nat. Acad. Sci. US 106(22):

    9105-9108.


Press Coverage:

New York Times, “ScienceTake: Flight of the Bumblebee,” Oct. 2013

BBC News & BBC Radio NewsHour, “Bumblebee flight inspires ‘bad    

    weather robot’ design,” Sept. 2013

Harvard Magazine, “Bees Knees: Taming Turbulence,” Nov-Dec 2009

Canadian Broadcasting Company, Quirks & Quarks radio program,    

    “The Bees’ Knees,” April 2006