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Lagrangian coherent structures in tandem flapping wing hovering

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Abstract

Lagrangian Coherent Structures (LCS) of tandem wings hovering in an inclined stroke plane is studied using Immersed-Boundary Method (IBM) by solving two dimensional (2D) incompressible Navier-Stokes equations. Coherent structures responsible for the force variation are visualized by calculating Finite Time Lyapunov Exponents (FTLE), and vorticity contours. LCS is effective in determining the vortex boundaries, flow separation, and the wing-vortex interactions accurately. The effects of inter-wing distance and phase difference on the force generation are studied. Results show that in-phase stroking generates maximum vertical force and counter-stroking generates the least vertical force. In-phase stroking generates a wake with swirl, and counter stroking generates a wake with predominant vertical velocity. Counter stroking aids the stability of the body in hovering. As the hindwing operates in the wake of the forewing, due to the reduction in the effective Angle of Attack (AoA), the hindwing generates lesser force than that of a single flapping wing.

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Authors and Affiliations

  1. Department of Applied Mechanics, Indian Institute of Technology Madras, Chennai, Tamil Nadu, India

    Srinidhi Nagarada Gadde & Sankaranarayanan Vengadesan

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  1. Srinidhi Nagarada Gadde
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  2. Sankaranarayanan Vengadesan
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Correspondence to Sankaranarayanan Vengadesan.

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Gadde, S.N., Vengadesan, S. Lagrangian coherent structures in tandem flapping wing hovering. J Bionic Eng 14, 307–316 (2017). https://doi.org/10.1016/S1672-6529(16)60399-2

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