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The development of helical vortex pairs in oscillatory flows – A numerical and experimental study

Lookup NU author(s): Dr Jonathan McDonoughORCiD, Professor Anh Phan, Professor Adam HarveyORCiD

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Abstract

© 2019 Elsevier B.V. When a liquid is oscillated in a tube containing a helical coil, there are two key flow phenomena: vortex-shedding and “swirl”. Together, they cause plug flow to be achievable over a wide range of conditions in this design. When an additional small cylindrical rod is placed in the centre of the helical coil, a new dual vortex regime is realised. This new flow regime was studied via CFD and PIV. It was demonstrated that a significant swirling velocity was generated by the helical coils, inducing an outward centrifugal force and inward pressure gradient, creating an instability resulting in the formation of a pair of counter-rotating vortices. The oscillatory amplitudes and frequencies necessary for the formation of these dual vortices at this scale (5 mm diameter) were centre-to-peak amplitude of 2–4 mm and frequency ≥ 3 Hz. The vortex pairs were also visualised in 3D, and exhibited a double-helix shape. Additionally, the transition of this flow to a more turbulent-like state was investigated. It was found to occur in the range Reo = 600–630. Through analysis of the swirl and radial numbers, it is clear that swirling dominates the flow structures at amplitudes of xo ≥ 4 mm.

Publication metadata

Author(s): McDonough JR, Ahmed SMR, Phan AN, Harvey AP

Publication type: Article

Publication status: Published

Journal: Chemical Engineering and Processing - Process Intensification

Year: 2019

Volume: 143

Print publication date: 01/09/2019

Online publication date: 06/07/2019

Acceptance date: 01/07/2019

Date deposited: 11/09/2019

ISSN (print): 0255-2701

ISSN (electronic): 1873-3204

Publisher: Elsevier BV

URL: https://doi.org/10.1016/j.cep.2019.107588

DOI: 10.1016/j.cep.2019.107588

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