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PhysRevFluids.8.084601.pdf (3.59 MB)

Oblique and parallel modes of the bistable bluff body wake

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posted on 2023-08-22, 09:11 authored by Simran PanesarSimran Panesar, Hao XiaHao Xia, Martin Passmore

Turbulent bluff body flows exhibit large-scale, low frequency dynamics associated with symmetry breaking in the wake which compromise stability and increase surface pressure drag. Previous tomographic PIV had detailed that these instabilities were associated with the stochastic reorientation of a hairpin featuring a near-base “head” connected to counter-rotating streamwise “tails” extending downstream. To better understand the associated flow physics, a half-axisymmetric bluff body is assessed by means of particle image velocimetry and pressure measurements. By application of proper orthogonal decomposition (POD) and an assessment of spanwise phase difference using a Morlet wavelet analysis, we show that the asymmetry of the wake region is intrinsically linked to a large scale circulation reversal responsible for the switch to the opposing symmetry breaking state. The antiphase relationship across the base is established by propagation of an oblique wave in the cross-stream direction at separation and as a result, the wake becomes twisted and skewed to one side inducing an asymmetric base pressure gradient. The two most energetic modes in the near wake are halved with respect to rectilinear bistable bodies; the first shows a helical topology with lateral asymmetry and the second shows a symmetry preserving condition with two counter rotating vortices at each side. Across the switch, the unsteady second mode briefly characterizes the wake. The associated parallel shedding regime with reduced asymmetry promotes axial motion (bubble pumping) which is coupled to an optimal, low drag condition.

Funding

Loughborough University

History

School

  • Aeronautical, Automotive, Chemical and Materials Engineering

Department

  • Aeronautical and Automotive Engineering

Published in

Physical Review Fluids

Volume

8

Issue

8

Publisher

American Physical Society

Version

  • VoR (Version of Record)

Rights holder

© The Authors

Publisher statement

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International (https://creativecommons.org/licenses/by/4.0/) license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Acceptance date

2023-07-12

Publication date

2023-08-09

Copyright date

2023

eISSN

2469-990X

Language

  • en

Depositor

Dr Hao Xia. Deposit date: 22 August 2023

Article number

084601

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