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Influence of three dimensionality on propulsive flapping

Influence of three dimensionality on propulsive flapping
Influence of three dimensionality on propulsive flapping
Propulsive flapping foils are widely studied in the development of swimming and flying animal-like autonomous systems. Numerical studies in this topic are mainly two-dimensional (2D) studies as they are quicker and cheaper, but, this inhibits the three-dimensional (3D) evolution of the shed vortices from leading- and trailing-edges. In this work, we examine the similarities and differences between 2D and 3D simulations through a case study in order to evaluate the efficacy and limitations of using 2D simulations to describe a 3D system. We simulate an infinite-span NACA0016 foil both in 2D and 3D at a Reynolds number of 5300 and an angle-of-attack of 10º. The foil is subject to prescribed heaving and pitching kinematics with varying trailing-edge deflection amplitude A. Our primary finding is that the flow and forces are effectively 2D at intermediate amplitude-based Strouhal numbers (StA = 2Af/U where U is the freestream velocity and f is the flapping frequency); StA ≈ 0.3 for heaving, StA ≈ 0.3–0.6 for pitching and StA ≈ 0.15–0.45 for coupled motion, while 3D effects dominate outside of these ranges. These 2D regions begin when the fluid energy induced by the flapping motion overcomes the 3D vortex shedding found on a stationary foil, and the flow reverts back to 3D when the strength of the shed vortices overwhelms the stabilizing influence of viscous dissipation. These results indicate that 3D-to-2D transitions or vice-versa are a balance between the strength and stability of leading-/trailing-edge vortices and the flapping energy. 2D simulations can still be used for flapping flight/swimming studies provided the flapping amplitude/frequency is within a given range.
0022-1120
A25-1-A25-14
Zurman Nasution, Andhini, Novrita
23daf17d-585b-4c53-b51a-8affd977b6e8
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052
Weymouth, Gabriel
b0c85fda-dfed-44da-8cc4-9e0cc88e2ca0
Zurman Nasution, Andhini, Novrita
23daf17d-585b-4c53-b51a-8affd977b6e8
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052
Weymouth, Gabriel
b0c85fda-dfed-44da-8cc4-9e0cc88e2ca0

Zurman Nasution, Andhini, Novrita, Ganapathisubramani, Bharathram and Weymouth, Gabriel (2020) Influence of three dimensionality on propulsive flapping. Journal of Fluid Mechanics, 886, A25-1-A25-14, [A25]. (doi:10.1017/jfm.2019.1078).

Record type: Article

Abstract

Propulsive flapping foils are widely studied in the development of swimming and flying animal-like autonomous systems. Numerical studies in this topic are mainly two-dimensional (2D) studies as they are quicker and cheaper, but, this inhibits the three-dimensional (3D) evolution of the shed vortices from leading- and trailing-edges. In this work, we examine the similarities and differences between 2D and 3D simulations through a case study in order to evaluate the efficacy and limitations of using 2D simulations to describe a 3D system. We simulate an infinite-span NACA0016 foil both in 2D and 3D at a Reynolds number of 5300 and an angle-of-attack of 10º. The foil is subject to prescribed heaving and pitching kinematics with varying trailing-edge deflection amplitude A. Our primary finding is that the flow and forces are effectively 2D at intermediate amplitude-based Strouhal numbers (StA = 2Af/U where U is the freestream velocity and f is the flapping frequency); StA ≈ 0.3 for heaving, StA ≈ 0.3–0.6 for pitching and StA ≈ 0.15–0.45 for coupled motion, while 3D effects dominate outside of these ranges. These 2D regions begin when the fluid energy induced by the flapping motion overcomes the 3D vortex shedding found on a stationary foil, and the flow reverts back to 3D when the strength of the shed vortices overwhelms the stabilizing influence of viscous dissipation. These results indicate that 3D-to-2D transitions or vice-versa are a balance between the strength and stability of leading-/trailing-edge vortices and the flapping energy. 2D simulations can still be used for flapping flight/swimming studies provided the flapping amplitude/frequency is within a given range.

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JFM Influence of Three Dimensionality on Propulsive Flapping_revision - Accepted Manuscript
Restricted to Repository staff only until 15 July 2020.
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Accepted/In Press date: 13 December 2019
e-pub ahead of print date: 15 January 2020
Published date: 10 March 2020

Identifiers

Local EPrints ID: 436680
URI: http://eprints.soton.ac.uk/id/eprint/436680
ISSN: 0022-1120
PURE UUID: f3ab5380-f845-4f65-9d87-ea460f82410f
ORCID for Andhini, Novrita Zurman Nasution: ORCID iD orcid.org/0000-0003-1924-3507
ORCID for Bharathram Ganapathisubramani: ORCID iD orcid.org/0000-0001-9817-0486
ORCID for Gabriel Weymouth: ORCID iD orcid.org/0000-0001-5080-5016

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Date deposited: 20 Dec 2019 18:29
Last modified: 07 Mar 2020 01:37

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