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EXPERIMENTAL INVESTIGATION OF A FLAPPING WING MODEL: SOME CHALLENGES FROM UNSTEADY AERODYNAMICS

Tatjana Hubel
Fachgebiet Stromungslehre und Aerodynamik, Technische Universitat Darmstadt Petersenstr. 30, D-64287 Darmstadt, Germany

Cameron Tropea
Technische Universität Darmstadt, Institute of Fluid Mechanics and Aerodynamics, Center of Smart Interfaces, International Research Training Group Darmstadt-Tokyo on Mathematical Fluid Dynamics, Germany

Abstrakt

A flapping-wing model has been experimentally investigated in the large (2.2m × 2.9m), low-speed wind tunnel of the Technische Universtitat Darmstadt. All tests were conducted at Reynolds numbers between 26,500 and 135,000 and throughout a range of reduced frequencies between 0.029 and 0.29, where the reduced frequency is defined as k=(πfc)/U(f is the wingbeat frequency, U the free-stream velocity, and c the average wing chord.) The relationships between flight parameters and the change in circulation during the course of a wing-beat cycle have been investigated. Particle Image Velocimetry (PIV), synchronized with the wing-beat cycle, has been used for flow field measurements and visualization. This yields the phase-averaged reconstruction of the flow field in measurement planes behind the wing parallel and perpendicular to the flow direction. This visualizes the shedding vortices from the wing trailing edge and the tip vortices in the far-field wake, respectively. The results of the flow visualization study are then used to calculate the phase resolved forces acting on the model.