JFM-19-S-0921.R2 final version.pdf (10.88 MB)
0/0

Salient three-dimensional features of the turbulent wake of a simplified square-back vehicle

Download (10.88 MB)
journal contribution
posted on 23.01.2020 by Giancarlo Pavia, Martin Passmore, Max Varney, Graham Hodgson
In this paper, the unsteady wake of a simplified square-back vehicle, with and without wheels, is investigated using large scale Tomographic Particle Image Velocimetry (TPIV), at a Reynolds number of ReH = 5.78 · 105 (based on the model height). In the no-wheel case, the time averaged wake features a balanced toroidal shape, with a good level of symmetry in both vertical and lateral directions. However analysis of the wake dynamics shows this widely accepted result to be a poor model of the wake structure. Application of Proper Orthogonal Decomposition (POD) to the unsteady data reveals the existence of the widely reported bi-stable behaviour, consisting of random switches between two
lateral symmetry breaking states. For the first time, the 3D topology of each state is fully characterised and the changes in wake topology during the switches between bistable states are also described. Each symmetry breaking state is shown to feature a characteristic ‘hairpin vortex’ structure that is the result of the merging of two horseshoe vortices, aligned with the vertical edges of the model base. The mutual interactions between these vortices are found to be at the origin of the bi-stable mode. The vertical symmetry is lost when wheels are added to the model, resulting in the formation of an upwash dominated wake. The bi-stable behaviour is removed but considerable mobility in the near-wake remains, in the form of a swinging motion of the rear recirculation.

Funding

Inst Sp - Feasibility studies in the application of Tomographic PIV to vehicle drag reduction - EPSRC Institutional Sponsorship Martin Passmore : EP/P511195/1

(EPSRC) Special Interest Group in Ground Vehicle Aerodynamics : Nick Daish

History

School

  • Aeronautical, Automotive, Chemical and Materials Engineering

Department

  • Aeronautical and Automotive Engineering

Published in

Journal of Fluid Mechanics

Volume

888

Publisher

Cambridge University Press (CUP)

Version

AM (Accepted Manuscript)

Rights holder

© The Authors

Publisher statement

This article has been published in a revised form in Journal of Fluid Mechanics https://doi.org/10.1017/jfm.2020.71. This version is published under a Creative Commons CC-BY-NC-ND. No commercial re-distribution or re-use allowed. Derivative works cannot be distributed. © The Authors.

Acceptance date

21/01/2020

Publication date

2020-02-17

Copyright date

2020

ISSN

0022-1120

eISSN

1469-7645

Language

en

Depositor

Prof Martin Passmore. Deposit date: 21 January 2020

Article number

A33

Exports

Logo branding

Categories

Exports