Seminar on Soft matter Hydrodynamics and (bio)Physics of Emergence (SHaPE)

Below you can read the title and abstract of his talk.

Investigating wing-wake interaction in the flight of the yellow fever mosquito.

The unsteady aerodynamics of flying insects are dominated by the formation and shedding of vortices. Of the two-winged (Dipteran) insects, mosquitoes represent a unique case: compared with other Diptera, their wings beat at a relatively high frequency, with a small amplitude. This unique kinematic condition appears
incompatible with current understanding of how vortex formation timescales are utilised by organisms for efficient propulsion1, and has been hypothesised2,3 to be the result of an evolutionary optimisation for acoustic tone production linked to mate selection. Conversely, some aerodynamic advantage to the observed low amplitude wingbeat kinematics has been claimed in the form of vortex wake capture4. It remains unclear however the extent to which wake capture effects contribute to force generation, under what conditions, and to what extent
this mitigates the seeming aerodynamic cost of the observed low amplitude beating behaviour.

I will present some recent work aimed at investigating such wing-wake interactions using the yellow fever mosquito, Aedes aegypti, as a model organism with low amplitude oscillatory wing beating kinematics. The three-dimensional wing beating kinematics of both male and female mosquitoes were first characterised in free-flight, using stereoscopic high-speed videography and machine learning5. The wingbeat pattern follows the “figure-of-eight”-type motion typical of Dipterans in hover, with wingbeat amplitude in the primary stroke plane of 40◦, and angular deviations out of this plane of approximately ±3◦. The range of angles pitched about the wing spanwise axis is ±50◦.

These kinematic data allow us to perform an aerodynamic analysis of the flight performance of such insects, aiming at understanding the importance of wing-wake interactions, and how the wing beating kinematics affect their strength. This was done numerically: The measured wing geometry and motions were immersed on a 3D Cartesian grid where the incompressible Navier-Stokes equations were solved in their finite-volume form. The boundary conditions on the immersed body were handled via the boundary data immersion method, as implemented in the WaterLily.jl package. We systematically varied key wing beating parameters around the observed free-flight behaviour, within a biologically relevant range, and characterised their effect on the forces due to wake capture, by reference to a predictive quasi-steady force model. The simulation allows for the visualization and tracking of the three-dimensional vortex structures produced by the beating mosquito wing, allowing us to interpret the forces due to wake capture in light of the interaction of the wing with its vortex wake.

Abel-John Buchner is working in the Laboratory for Aero and Hydrodynamics, Delft University of Technology, The Netherlands.