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Deflected wake interaction of tandem flapping foils

Deflected wake interaction of tandem flapping foils
Deflected wake interaction of tandem flapping foils
Symmetric flapping foils are known to produce deflected jets at high frequency–amplitude combinations even at a zero mean angle of attack. This reduces the frequency range of useful propulsive configurations without side force. In this study, we numerically analyse the interaction of these deflected jets for tandem flapping foils undergoing coupled heave-to-pitch motion in a two-dimensional domain. The impact of the flapping Strouhal number, foil spacing and phasing on wake interaction is investigated. Our primary finding is that the back foil is capable of cancelling the wake deflection and mean side force of the front foil, even when located up to five chord lengths downstream. This is achieved by attracting the incoming dipoles and disturbing their cohesion within the limits of the back foil’s range of flapping motion. We also show that the impact on cycle-averaged thrust varies from high augmentation to drag generation depending on the wake patterns downstream of the back foil. These findings provide new insights towards the design of biomimetic tandem propulsors, as they expand their working envelope and ability to rapidly increase or decrease the forward speed by manipulating the size of the shed vortices.
flow-structure interactions, vortex interactions, wakes
0022-1120
Lagopoulos, Nikolaos
8a38fce1-8fa9-4dec-a2b0-db0e9372c575
Weymouth, Gabriel
b0c85fda-dfed-44da-8cc4-9e0cc88e2ca0
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052
Lagopoulos, Nikolaos
8a38fce1-8fa9-4dec-a2b0-db0e9372c575
Weymouth, Gabriel
b0c85fda-dfed-44da-8cc4-9e0cc88e2ca0
Ganapathisubramani, Bharathram
5e69099f-2f39-4fdd-8a85-3ac906827052

Lagopoulos, Nikolaos, Weymouth, Gabriel and Ganapathisubramani, Bharathram (2020) Deflected wake interaction of tandem flapping foils. Journal of Fluid Mechanics, 903, [2020640]. (doi:10.1017/jfm.2020.640).

Record type: Article

Abstract

Symmetric flapping foils are known to produce deflected jets at high frequency–amplitude combinations even at a zero mean angle of attack. This reduces the frequency range of useful propulsive configurations without side force. In this study, we numerically analyse the interaction of these deflected jets for tandem flapping foils undergoing coupled heave-to-pitch motion in a two-dimensional domain. The impact of the flapping Strouhal number, foil spacing and phasing on wake interaction is investigated. Our primary finding is that the back foil is capable of cancelling the wake deflection and mean side force of the front foil, even when located up to five chord lengths downstream. This is achieved by attracting the incoming dipoles and disturbing their cohesion within the limits of the back foil’s range of flapping motion. We also show that the impact on cycle-averaged thrust varies from high augmentation to drag generation depending on the wake patterns downstream of the back foil. These findings provide new insights towards the design of biomimetic tandem propulsors, as they expand their working envelope and ability to rapidly increase or decrease the forward speed by manipulating the size of the shed vortices.

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Accepted/In Press date: 24 July 2020
e-pub ahead of print date: 18 September 2020
Published date: 25 November 2020
Keywords: flow-structure interactions, vortex interactions, wakes

Identifiers

Local EPrints ID: 444099
URI: http://eprints.soton.ac.uk/id/eprint/444099
ISSN: 0022-1120
PURE UUID: ce2675b6-1484-4892-94bf-290806450c75
ORCID for Gabriel Weymouth: ORCID iD orcid.org/0000-0001-5080-5016
ORCID for Bharathram Ganapathisubramani: ORCID iD orcid.org/0000-0001-9817-0486

Catalogue record

Date deposited: 24 Sep 2020 16:44
Last modified: 18 Feb 2021 17:21

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