Hostname: page-component-5cf477f64f-bmd9x Total loading time: 0 Render date: 2025-04-03T09:32:13.858Z Has data issue: false hasContentIssue false
  • English
  • Français

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

Published online by Cambridge University Press:  17 February 2020

G. Pavia Open the ORCID record for G. Pavia [Opens in a new window] ,
M. A. Passmore ,
M. Varney  and
G. Hodgson
G. Pavia*
Affiliation:
AAE Department, Stewart Miller Building, Loughborough University, LoughboroughLE11 3TU, UK
M. A. Passmore*
Affiliation:
AAE Department, Stewart Miller Building, Loughborough University, LoughboroughLE11 3TU, UK
M. Varney
Affiliation:
AAE Department, Stewart Miller Building, Loughborough University, LoughboroughLE11 3TU, UK
G. Hodgson
Affiliation:
AAE Department, Stewart Miller Building, Loughborough University, LoughboroughLE11 3TU, UK
*
†Email addresses for correspondence: [email protected], [email protected]
†Email addresses for correspondence: [email protected], [email protected]
Get access Rights & Permissions [Opens in a new window]

Abstract

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, at a Reynolds number of $Re_{H}=5.78\times 10^{5}$ (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 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 three-dimensional topology of each state is fully characterised and the changes in wake topology during the switches between bi-stable 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.

JFM classification

Wakes/Jets: Separated flows
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 888 , 10 April 2020 , A33
Copyright
© The Author(s), 2020. Published by Cambridge University Press

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Atkinson, C. & Soria, J. 2009 An efficient simultaneous reconstruction technique for tomographic particle image velocimetry. Exp. Fluids 47 (4–5), 553.CrossRefGoogle Scholar
Barros, D., Borée, J., Cadot, O., Spohn, A. & Noack, B. R. 2017 Forcing symmetry exchanges and flow reversals in turbulent wakes. J. Fluid Mech. 829, R1.CrossRefGoogle Scholar
Bonnavion, G. & Cadot, O. 2018 Unstable wake dynamics of rectangular flat-backed bluff bodies with inclination and ground proximity. J. Fluid Mech. 854, 196–232.CrossRefGoogle Scholar
Bonnavion, G. & Cadot, O. 2019 Boat-tail effects on the global wake dynamics of a flat-backed body with rectangular section. J. Fluids Struct. 89, 61–71.CrossRefGoogle Scholar
Bonnavion, G., Cadot, O., Évrard, A., Herbert, V., Parpais, S., Vigneron, R. & Délery, J. 2017 On multistabilities of real car’s wake. J. Wind Engng Ind. Aerodyn. 164, 22–33.CrossRefGoogle Scholar
Bonnavion, G., Cadot, O., Herbert, V., Parpais, S., Vigneron, R. & Délery, J. 2019 Asymmetry and global instability of real minivans’ wake. J. Wind Engng Ind. Aerodyn. 184, 77–89.CrossRefGoogle Scholar
Brackston, R. D., Wynn, A. & Morrison, J. F. 2018 Modelling and feedback control of vortex shedding for drag reduction of a turbulent bluff body wake. Intl J. Heat Fluid Flow 71, 127–136.CrossRefGoogle Scholar
Cadot, O., Evrard, A. & Pastur, L. 2015 Imperfect supercritical bifurcation in a three-dimensional turbulent wake. Phys. Rev. E 91 (6), 063005.Google Scholar
Ceglia, G., Discetti, S., Ianiro, A., Michaelis, D., Astarita, T. & Cardone, G. 2014 Three-dimensional organization of the flow structure in a non-reactive model aero engine lean burn injection system. Exp. Therm. Fluid Sci. 52, 164–173.CrossRefGoogle Scholar
Dalla Longa, L., Evstafyeva, O. & Morgans, A. S. 2019 Simulations of the bi-modal wake past three-dimensional blunt bluff bodies. J. Fluid Mech. 866, 791–809.CrossRefGoogle Scholar
Discetti, S. & Astarita, T. 2012 A fast multi-resolution approach to tomographic PIV. Exp. Fluids 52 (3), 765–777.CrossRefGoogle Scholar
Elsinga, G. E., Scarano, F., Wieneke, B. & van Oudheusden, B. W. 2006 Tomographic particle image velocimetry. Exp. Fluids 41 (6), 933–947.CrossRefGoogle Scholar
Evrard, A., Cadot, O., Herbert, V., Ricot, D., Vigneron, R. & Délery, J. 2016 Fluid force and symmetry breaking modes of a 3D bluff body with a base cavity. J. Fluids Struct. 61, 99–114.CrossRefGoogle Scholar
Evstafyeva, O.2018 Simulation and feedback control of simplified vehicle flows. PhD thesis, Imperial College London.Google Scholar
Faranda, D., Sato, Y., Saint-Michel, B., Wiertel, C., Padilla, V., Dubrulle, B. & Daviaud, F. 2017 Stochastic chaos in a turbulent swirling flow. Phys. Rev. Lett. 119 (1), 014502.CrossRefGoogle Scholar
Grandemange, M., Cadot, O., Courbois, A., Herbert, V., Ricot, D., Ruiz, T. & Vigneron, R. 2015 A study of wake effects on the drag of Ahmed’s squareback model at the industrial scale. J. Wind Engng Ind. Aerodyn. 145, 282–291.CrossRefGoogle Scholar
Grandemange, M., Gohlke, M. & Cadot, O. 2013a Bi-stability in the turbulent wake past parallelepiped bodies with various aspect ratios and wall effects. Phys. Fluids 25 (9), 95–103.CrossRefGoogle Scholar
Grandemange, M., Gohlke, M. & Cadot, O. 2013b Turbulent wake past a three-dimensional blunt body. Part 1. Global modes and bi-stability. J. Fluid Mech. 722, 51–84.CrossRefGoogle Scholar
Grandemange, M., Gohlke, M. & Cadot, O. 2014 Turbulent wake past a three-dimensional blunt body. Part 2. Experimental sensitivity analysis. J. Fluid Mech. 752, 439–461.CrossRefGoogle Scholar
Jeong, J. & Hussain, F. 1995 On the identification of a vortex. J. Fluid Mech. 285, 69–94.CrossRefGoogle Scholar
Johl, G., Passmore, M. & Render, P. 2004 Design methodology and performance of an indraft wind tunnel. Aeronaut. J. 108 (1087), 465–473.CrossRefGoogle Scholar
Li, R., Barros, D., Borée, J., Cadot, O., Noack, B. R. & Cordier, L. 2016 Feedback control of bimodal wake dynamics. Exp. Fluids 57 (10), 158.CrossRefGoogle Scholar
Lucas, J.-M., Cadot, O., Herbert, V., Parpais, S. & Délery, J. 2017 A numerical investigation of the asymmetric wake mode of a squareback Ahmed body-effect of a base cavity. J. Fluid Mech. 831, 675–697.CrossRefGoogle Scholar
Lumley, J. L. 1967 The structure of inhomogeneous turbulent flows. In Atmospheric Turbulence Radio Wave Propagation (ed. Yaglom, A. M. & Tatarski, V. I.), pp. 166–178. Nauka.Google Scholar
Pavia, G.2019 Characterisation of the unsteady wake of a square-back road vehicle. PhD thesis, Loughborough University.Google Scholar
Pavia, G. & Passmore, M. 2017 Characterisation of wake bi-stability for a square-back geometry with rotating wheels. In FKFS Conference, pp. 93–109. Springer.Google Scholar
Pavia, G., Passmore, M. & Gaylard, A.2016 Influence of short rear end tapers on the unsteady base pressure of a simplified ground vehicle. Tech. Rep. SAE Technical Paper.CrossRefGoogle Scholar
Pavia, G., Passmore, M. & Sardu, C. 2018 Evolution of the bi-stable wake of a square-back automotive shape. Exp. Fluids 59 (1), 20.CrossRefGoogle Scholar
Pavia, G., Passmore, M. & Varney, M. 2019a Low-frequency wake dynamics for a square-back vehicle with side trailing edge tapers. J. Wind Engng Ind. Aerodyn. 184, 417–435.CrossRefGoogle Scholar
Pavia, G., Varney, M., Passmore, M. & Almond, M. 2019b Three dimensional structure of the unsteady wake of an axisymmetric body. Phys. Fluids 31 (2), 025113.CrossRefGoogle Scholar
Perry, A.-K., Almond, M., Passmore, M. & Littlewood, R. 2016a The study of a bi-stable wake region of a generic squareback vehicle using tomographic PIV. SAE Intl J. Passenger Cars-Mech. Syst. 9 (2), 743–754.CrossRefGoogle Scholar
Perry, A.-K., Pavia, G. & Passmore, M. 2016b Influence of short rear end tapers on the wake of a simplified square-back vehicle: wake topology and rear drag. Exp. Fluids 57 (11), 169.CrossRefGoogle Scholar
Rouméas, M., Gilliéron, P. & Kourta, A. 2009 Analysis and control of the near-wake flow over a square-back geometry. Comput. Fluids 38 (1), 60–70.CrossRefGoogle Scholar
Sae2010 Surface vehicle recommended practice. Tech. Rep. J1594. SAE International.Google Scholar
Scarano, F. 2012 Tomographic PIV: principles and practice. Meas. Sci. Technol. 24 (1), 012001.Google Scholar
Scarano, F., Ghaemi, S., Caridi, G. C. A., Bosbach, J., Dierksheide, U. & Sciacchitano, A. 2015 On the use of helium-filled soap bubbles for large-scale tomographic PIV in wind tunnel experiments. Exp. Fluids 56 (2), 42.CrossRefGoogle Scholar
Sellappan, P., McNally, J. & Alvi, F. S. 2018 Time-averaged three-dimensional flow topology in the wake of a simplified car model using volumetric PIV. Exp. Fluids 59 (8), 124.CrossRefGoogle Scholar
Sirovich, L. 1987 Turbulence and the dynamics of coherent structures. 1. Coherent structures. Q. Appl. Maths 45 (3), 561–571.CrossRefGoogle Scholar
Taira, K., Brunton, S. L., Dawson, S. T. M., Rowley, C. W., Colonius, T., McKeon, B. J., Schmidt, O. T., Gordeyev, S., Theofilis, V. & Ukeiley, L. S. 2017 Modal analysis of fluid flows: an overview. AIAA J. 4013–4041.CrossRefGoogle Scholar
de la Torre, A. & Burguete, J. 2007 Slow dynamics in a turbulent von Kármán swirling flow. Phys. Rev. Lett. 99 (5), 054101.CrossRefGoogle Scholar
Varney, M., Passmore, M. & Gaylard, A. 2018 Parametric study of asymmetric side tapering in constant cross wind conditions. SAE Intl J. Passenger Cars-Mech. Syst. 11 (06-11-03-0018), 213–224.CrossRefGoogle Scholar
Varon, E., Eulalie, Y., Edwige, S., Gilotte, P. & Aider, J.-L. 2017 Chaotic dynamics of large-scale structures in a turbulent wake. Phys. Rev. Fluids 2 (3), 034604.CrossRefGoogle Scholar
Volpe, R., Devinant, P. & Kourta, A. 2015 Experimental characterization of the unsteady natural wake of the full-scale square back Ahmed body: flow bi-stability and spectral analysis. Exp. Fluids 56 (5), 1–22.CrossRefGoogle Scholar
Westerweel, J. & Scarano, F. 2005 Universal outlier detection for PIV data. Exp. Fluids 39 (6), 1096–1100.CrossRefGoogle Scholar
Wieneke, B. 2008 Volume self-calibration for 3D particle image velocimetry. Exp. Fluids 45 (4), 549–556.CrossRefGoogle Scholar

Pavia et al. supplementary movie 1

Temporal evolution of the wake’s recirculation for the configuration with no wheels. Results obtained combining the time averaged field with the first POD mode.

Download Pavia et al. supplementary movie 1(Video)
Video 2.7 MB

Pavia et al. supplementary movie 2

Temporal evolution of the wake’s recirculation for the configuration with no wheels. Results obtained combining the time averaged field with the first two POD modes.

Download Pavia et al. supplementary movie 2(Video)
Video 2.8 MB

Pavia et al. supplementary movie 3

Temporal evolution of the wake’s recirculation for the configuration with no wheels. Results obtained combining the time averaged field with the first three POD modes.

Download Pavia et al. supplementary movie 3(Video)
Video 3 MB

Pavia et al. supplementary movie 4

Temporal evolution of the wake’s recirculation for the configuration with wheels. Results obtained combining the time averaged field with the first POD mode.

Download Pavia et al. supplementary movie 4(Video)
Video 3.2 MB