Aerodynamics of Flapping Wing at Low Reynolds Numbers: Force Measurement and Flow Visualization

Abhijit Banerjee,Saurav K Ghosh,Debopam Das

doi:10.5402/2011/162687

Abhijit Banerjee, Saurav K Ghosh + Show 1 more

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https://doi.org/10.5402/2011/162687

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Abstract

Flow field of a butterfly mimicking flapping model with plan form of various shapes and butterfly-shaped wings is studied. The nature of the unsteady flow and embedded vortical structures are obtained at chord cross-sectional plane of the scaled wings to understand the dynamics of insect flapping flight. Flow visualization and PIV experiments are carried out for the better understanding of the flow field. The model being studied has a single degree of freedom of flapping. The wing flexibility adds another degree to a certain extent introducing feathering effect in the kinematics. The mechanisms that produce high lift and considerable thrust during the flapping motion are identified. The effect of the Reynolds number on the flapping flight is studied by varying the wing size and the flapping frequency. Force measurements are carried out to study the variations of lift forces in the Reynolds number (Re) range of 3000 to 7000. Force experiments are conducted both at zero and finite forward velocity in a wind tunnel. Flow visualization as well as PIV measurement is conducted only at zero forward velocity in a stagnant water tank and in air, respectively. The aim here is to measure the aerodynamic lift force and visualize the flow field and notice the difference with different Reynolds number (Re), and flapping frequency (f), and advance ratios (J=U∞/2ϕfR).

Highlights

With the advent in the progressive research for the application and fabrication of autonomous MAVs flapping mode flight is largely and widely studied in the past couple of decades
Reynolds number here is defined in terms of tip-speed (Vt) whereas with forward velocity Reynolds number is defined in terms of U∞
The leading edge vortex (LEV) and interaction between these two vortex rings formed around the wing, and its movement in an angular direction with respect to the wing is mainly responsible for the unusually high lift generated by insects

Summary

Introduction

With the advent in the progressive research for the application and fabrication of autonomous MAVs (micro aero vehicles) flapping mode flight is largely and widely studied in the past couple of decades. Another development is the onset of the MAVs with flapping wings type The edge of this mode of flying type comes in terms of efficiency, maneuverability, and wide range of speed, which is perhaps the reason of its presence in nature among millions of species of birds and insects. This flapping wing flight is much more complex in terms of unsteadiness and three-dimensional nature, which cannot be summed up by conventional aerodynamics alone. Some progress have been made using quasisteady and unsteady aerodynamics of simple flapping kinematics [1, 2], but the forces and control over them encountered is far more complicated owing to its dependence on wide array of aerodynamic mechanisms to take off, maneuver, maintain steady flight, and for landing [3]

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