Title:
Plant-pollinator aerodynamics
Plant-pollinator aerodynamics
Author(s)
Matthews, Megan
Advisor(s)
Sponberg, Simon
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Abstract
Interactions between plants and pollinators have adapted over long evolutionary timescales and fill a vital ecological role. For flying pollinators, the same coherent aerodynamic mechanisms are employed across the broad Reynolds number range of 100-10,000. This thesis aims to understand some of the physics involved in plant-pollinator aerodynamics. First, studying the impact of an artificial flower wake on maneuverability revealed emergent simplicity in hawkmoth flower tracking dynamics with increased tracking error at the vortex shedding frequencies of the 3D-printed flower. These results establish that unsteady flow affects complex behaviors as well as steady flight performance. Next, the interplay between steady airflow and wing flexibility was explored in two flow regimes: (1) matching airflow conditions for Manduca sexta flight and (2) matching flow conditions known to produce decoherent leading-edge vortices (LEVs) on rigid wings. Although LEVs still burst on flexible hawkmoth wings, the LEV is decoherent over more of the wingspan as flexibility decreases. Enhanced LEV stability in the hawkmoth flight regime revealed that trade-offs between Coriolis forces (from wing rotation) and inertial forces (from both wing translation and the incoming airflow) influence LEV structure and lift force. Last, the wakes of hawkmoth-pollinated flowers were found to be turbulent but some irregular periodic structures were present downstream of small flowers (diameter less than 40 mm). Like many bluff body flow interactions, flower wakes are dominated by a re-circulation zone downstream and hawkmoths hover-feed within the re-circulation bubble. In addition to characterizing the local flow environment for a hovering hawkmoth, this work showed how flow in the flower wake impacts aerodynamic force (with a blade-element model). Despite the broad diversity in floral environments for pollinators, flapping flight (and the LEV in particular) remains a highly effective strategy. Future work can investigate how insects achieve consistent performance across variable environments from behavioral, neurological, and aerodynamic perspectives.
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Date Issued
2021-08-26
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Dissertation