Meeting Abstract
Flying insects interact with changing aerial environments that may challenge aerodynamic performance. Both floral pollinators and the flowers they seek are affected by changes in airflow. Recent studies have begun to explore how animals alter behavior in response to unsteady air, but we do not know if these conditions represent the airflow behind natural flowers. Wind may blow from multiple directions and evidence suggests that flowers can re-orient to face downstream which means that pollinators would often fly through flower wakes. To investigate the features of a natural flower wake, we used 3D particle tracking velocimetry (3D-PTV) to measure the flow downstream of Petunia hybrids varying in diameter from 2-4.6 cm. The 3D wakes for all flowers showed an unsteady region of reduced wind velocity, comparable in size to the flower diameter, that extended 3-6 cm downstream. The unsteady region was present in all flower sizes, but we found that wakes of large flowers were dominated by a steady downwash. Flowers with d=4.6 cm induced a 10°-20° deflection of the freestream airflow that persists up to 2 cm above the petal height. Next, we determined the aerodynamic consequences of the steady induced wake angle for a hawkmoth hovering downstream with a blade-element model (BEM). At 0.7 m/s, a 20° difference in the incoming airflow results in a 9% loss in vertical force due to changes in effective angle of attack. During pollination, insects must reach the flower and maintain contact while interacting with the deflected flower wake, but the reduction in force suggests that animals would need to alter flight posture and/or kinematics to maintain performance, even at low wind speeds. Our work shows that flower wakes can incur significant losses in flight performance for pollinators.
