A computational investigation of the three-dimensional unsteady aerodynamics of<i>Drosophila</i>hovering and maneuvering

TLDR

The study identifies the unsteady aerodynamic origin of the time‑varying yaw moment. Three‑dimensional unsteady CFD simulations of a fruit fly, using experimentally prescribed wing and body kinematics, compute flow fields and center‑of‑pressure distributions to analyze yaw‑moment generation. The simulations show that lift and thrust agree with experiments, and that subtle asymmetries in wing kinematics generate a yaw moment whose peak occurs at maneuver onset, with forward and lift forces producing the turning moment while side forces provide restoring torque, and reveal novel Lambda‑shaped vortex structures in the wake.

Abstract

Three-dimensional unsteady computations of the flow past a fruit fly Drosophila under hovering and free flight conditions are computed. The kinematics of the wings and the body of the fruit fly are prescribed from experimental observations. The computed unsteady lift and thrust forces are validated with experimental results and are in excellent agreement. The unsteady aerodynamic origin of the time-varying yaw moment is identified. The differences in the kinematics between the right and the left wings show that subtle change in the stroke angle and deviation angle can result in the yaw moment for the turning maneuver. The computed yaw moment reaches a peak value at the beginning of the maneuver and remains positive throughout the remainder of the maneuver. The origin of the yaw moment is investigated by computing the center of pressures on each wing and the individual moment arms. This investigation leads to the conclusion that it is the forward force and a component of the lift force that combine to produce the turning moment while the side force alone produces the restoring torque during the maneuver. The vorticity shed from the wing's leading edge and the tips show a loop like structure that during stroke reversals pinches off into Lambda-like structures that have not been previously observed in the wakes of flapping fliers.