Smart wing rotation and trailing-edge vortices enable high frequency mosquito flight

Abstract

SummaryMosquitoes exhibit unique wing kinematics; their long, slender wings flap at remarkably high frequencies for their size (>800 Hz) and with lower stroke amplitudes than any other insect group1. This shifts weight support away from the translation-dominated, aerodynamic mechanisms used by most insects2, as well as by helicopters and aeroplanes, towards poorly understood rotational mechanisms that occur when pitching at the end of each half-stroke. Here we report wing kinematics and solve the full Navier-Stokes equations using computational fluid dynamics with overset grids and validate our results with in vivo flow measurements. We show that, while familiar separated flow patterns are used by mosquitoes, much of the aerodynamic force that supports their weight is generated in a manner unlike any previously described flying animal. In total, there are three key features: leading-edge vortices (a well-known mechanism that appears to be almost ubiquitous in insect flight), trailing-edge vortices caused by a novel form of wake capture at stroke reversal, and rotational drag. The two new elements are largely independent of the wing velocity, instead relying on rapid changes in the pitch angle (wing rotation) at the end of each half stroke, and are therefore relatively immune to the shallow flapping amplitude. Moreover, these mechanisms are particularly well-suited to high-aspect ratio mosquito wings.

Escaping blood-fed malaria mosquitoes minimize tactile detection without compromising on take-off speed

“…This is most likely because of the limitations of our quasi-steady aerodynamic model which did not include several unsteady aerodynamic mechanisms, such as wake capture and added mass (Dickinson and Muijres, 2016). These unsteady aerodynamic mechanisms might thus become increasingly more important with greater force production; in particular, trailing-edge vortex lift, which was recently described in flying mosquitoes, might play an important role here (Bomphrey et al, 2017). Future research into the detailed aerodynamics of mosquito flight is required to answer this question.…”

“…For the model, we used the functions of lift and drag coefficients versus angle of attack [C L (α) and C D (α), respectively] and the rotational lift coefficients (C rot =1.55) determined using a robotic insect wing model, as mosquitoes operate at a Reynolds number similar to that used in the robot (Sane and Dickinson, 2002). This quasi-steady model captures aerodynamic force production remarkably well in flapping fruit fly wings (Dickinson and Muijres, 2016;Sane and Dickinson, 2002), but it does not simulate unsteady aerodynamic effects, such as wake capture, added mass or the trailing-edge vortex lift that was recently identified as an important lift generator in flying mosquitoes (Bomphrey et al, 2017). This recent study on the aerodynamics of male Culex mosquitoes also developed a quasi-steady aerodynamic model (Bomphrey et al, 2017).…”

“…4) shows that, similar to Culex mosquitoes (Bomphrey et al, 2017), steadily flying unfed malaria mosquitoes operate at exceptionally low wingbeat amplitudes (A stroke =42 deg) and high wingbeat frequencies ( f=579 Hz; Fig. 4I,L, Table S3).…”

“…This quasi-steady model captures aerodynamic force production remarkably well in flapping fruit fly wings (Dickinson and Muijres, 2016;Sane and Dickinson, 2002), but it does not simulate unsteady aerodynamic effects, such as wake capture, added mass or the trailing-edge vortex lift that was recently identified as an important lift generator in flying mosquitoes (Bomphrey et al, 2017). This recent study on the aerodynamics of male Culex mosquitoes also developed a quasi-steady aerodynamic model (Bomphrey et al, 2017). This model produced different estimates for C L (α) and C D (α), which might be because it is based on computational fluid dynamics simulations rather than robotic model experiments, or (more likely) because it was based on simulations of high-aspect ratio mosquito wings.…”

“…A recent study on the flight dynamics and aerodynamics of Culex mosquitoes (Bomphrey et al, 2017) showed that mosquitoes operate at extremely low wingbeat amplitudes (∼40 deg) and high wingbeat frequencies (∼700 Hz). To achieve this, mosquitoes make use of specialized aerodynamic mechanisms controlled by spanwise wing rotations, but the functional reason for using these extreme wingbeat kinematics is unknown (Bomphrey et al, 2017).…”