Rasche Richtungsänderungen und Torsionen schwingender Fliegenflügel und Hypothesen über zugeordnete instationäre Strömlingseffekte

Summary

A detailed kinematical analysis of oscillating fly wings using high speed cine films in three-table projection and model reconstructions show a variety of quick changes in beating and rotating movements. There are especially quick changes in the geometrical angle of attack during the upper and lower reversal phases and quick twisting movements and bending oscillations during some of the beating phases. A dozen possibilities for instationary aerodynamic effects are discussed, including quick oscillations in angle of attack, quick turning movements in the reversal points, circulation possibly induced by a quick supination during the beginning of upstroke (fast supination effect), oblique attack by the fluid, circulation possibly induced by a forced oscillation of the trailing edge during the beginning of downstroke (swinging edge effect), tangential transport of the boundary layer by undulatory movements, rolling movements during the turning phases, high-frequency small oscillations of the wing surface, and a quick oscillation during late upstroke. Weis-Fogh's ‘clap and fling mechanism’ and ‘flip mechanism’ could not be detected in Calliphorid flies.