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The influence of background turbulence on Ahmed-body wake bistability

Published online by Cambridge University Press:  06 September 2021

D. Burton ,
S. Wang ,
D. Tudball Smith ,
H. N. Scott ,
T. N. Crouch  and
M. C. Thompson
D. Burton*
Affiliation:
Monash Wind Tunnel Research Platform, Monash University, Clayton, VIC3800, Australia Fluids Laboratory for Aeronautical and Industrial Research (FLAIR), Monash University, Clayton, VIC3800, Australia Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC3800, Australia
S. Wang
Affiliation:
Monash Wind Tunnel Research Platform, Monash University, Clayton, VIC3800, Australia Fluids Laboratory for Aeronautical and Industrial Research (FLAIR), Monash University, Clayton, VIC3800, Australia Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC3800, Australia
D. Tudball Smith
Affiliation:
Monash Wind Tunnel Research Platform, Monash University, Clayton, VIC3800, Australia Fluids Laboratory for Aeronautical and Industrial Research (FLAIR), Monash University, Clayton, VIC3800, Australia Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC3800, Australia
H. N. Scott
Affiliation:
Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC3800, Australia
T. N. Crouch
Affiliation:
Monash Wind Tunnel Research Platform, Monash University, Clayton, VIC3800, Australia Fluids Laboratory for Aeronautical and Industrial Research (FLAIR), Monash University, Clayton, VIC3800, Australia Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC3800, Australia
M. C. Thompson
Affiliation:
Monash Wind Tunnel Research Platform, Monash University, Clayton, VIC3800, Australia Fluids Laboratory for Aeronautical and Industrial Research (FLAIR), Monash University, Clayton, VIC3800, Australia Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC3800, Australia
*
†Email address for correspondence: [email protected]
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Abstract

The discovery of wake bistability has generated an upsurge in experimental investigations into the wakes of simplified vehicle geometries. Particular focus has centred on the probabilistic switching between two asymmetrical bistable wake states of a square-back Ahmed body; however, the majority of this research has been undertaken in wind tunnels with turbulence intensities of less than $1\,\%$, considerably lower than typical atmospheric levels. To better simulate bistability under on-road conditions, in which turbulence intensities can easily reach levels of $10\,\%$ or more, this experimental study investigates the effects of free-stream turbulence on the bistability characteristics of the square-back Ahmed body. Through passive generation and quantification of the free-stream turbulent conditions, a monotonic correlation was found between the switching rate and free-stream turbulence intensity.

JFM classification

Wakes/Jets: Wakes Vortex Flows: Vortex shedding Wakes/Jets: Separated flows
Type
JFM Rapids
Information
Journal of Fluid Mechanics , Volume 926 , 10 November 2021 , R1
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Copyright
© The Author(s), 2021. Published by Cambridge University Press

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References

REFERENCES

Ahmed, S.R., Ramm, G. & Faltin, G. 1984 Some salient features of the time-averaged ground vehicle wake. SAE Tech. Paper (No. 840300).Google 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.Google Scholar
Bergh, H. & Tijdeman, H. 1965 Theoretical and Experimental Results for the Dynamic Response of Pressure Measuring Systems. Nationaal lucht- en ruimtevaartlaboratorium.Google 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.Google 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.Google Scholar
Brackston, R.D., de la Cruz, J.M.G., Wynn, A., Rigas, G. & Morrison, J.F. 2016 Stochastic modelling and feedback control of bistability in a turbulent bluff body wake. J. Fluid Mech. 802, 726–749.Google Scholar
Cadot, O., Almarzooqi, M., Legeai, A., Parezanović, V. & Pastur, L. 2020 On three-dimensional bluff body wake symmetry breaking with free-stream turbulence and residual asymmetry. C. R. Méc. 348 (6–7), 509–517.Google 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
Cogotti, A. 2003 Generation of a controlled level of turbulence in the pininfarina wind tunnel for the measurement of unsteady aerodynamics and aeroacoustics. SAE Tech. Paper SP-1786 (2003-01-0430).Google 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. 886, 791–809.Google Scholar
Evstafyeva, O., Morgans, A.S. & Dalla Longa, L. 2017 Simulation and feedback control of the ahmed body flow exhibiting symmetry breaking behaviour. J. Fluid Mech. 817, R2.Google Scholar
Grandemange, M., Cadot, O. & Gohlke, M. 2012 Reflectional symmetry breaking of the separated flow over three-dimensional bluff bodies. Phys. Rev. E 86 (3), 035302.CrossRefGoogle ScholarPubMed
Grandemange, M., Gohlke, M. & Cadot, O. 2013 Bi-stability in the turbulent wake past parallelepiped bodies with various aspect ratios and wall effects. Phys. Fluids 25 (9), 095103.CrossRefGoogle Scholar
Grandemange, M., Gohlke, M. & Cadot, O. 2013 b 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
Haffner, Y., Borée, J., Spohn, A. & Castelain, T. 2020 Mechanics of bluff body drag reduction during transient near-wake reversals. J. Fluid Mech. 894, A14.CrossRefGoogle Scholar
Herry, B.B., Keirsbulck, L., Labraga, L. & Paquet, J.-B. 2011 Flow bistability downstream of three-dimensional double backward facing steps at zero-degree sideslip. Trans. ASME: J. Fluids Engng 133 (5), 054501.Google Scholar
Hooper, J.D. & Musgrove, A.R. 1997 Reynolds stress, mean velocity, and dynamic static pressure measurement by a four-hole pressure probe. Expl Therm. Fluid Sci. 15 (4), 375–383.CrossRefGoogle Scholar
Kang, N., Essel, E.E., Roussinova, V. & Balachandar, R. 2021 Effects of approach flow conditions on the unsteady three-dimensional wake structure of a square-back Ahmed body. Phys. Rev. Fluids 6, 034613.CrossRefGoogle Scholar
von Kármán, T. 1948 Progress in the statistical theory of turbulence. Proc. Natl Acad. Sci. USA 34 (11), 530–539.CrossRefGoogle ScholarPubMed
Li, R. 2017 Aerodynamic drag reduction of a square-back car model using linear genetic programming and physics-based control. PhD thesis, ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique, Poitiers.Google Scholar
Lorite-Díez, M., Jimínez-González, J.I., Pastur, L., Martínez-Bazán, C. & Cadot, O. 2020 Experimental analysis of the effect of local base blowing on three-dimensional wake modes. J. Fluid Mech. 883, A53.CrossRefGoogle Scholar
O'Neill, P., Nicolaides, D., Honnery, D. & Soria, J. 2004 Autocorrelation functions and the determination of integral length with reference to experimental and numerical data. In Proceedings of the Fifteenth Australasian Fluid Mechanics Conference (ed. M. Behnia, W. Lin & G.D. McBain), pp. 1–4. University of Sydney.Google 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
Rigas, G., Morgans, A.S., Brackston, R.D. & Morrison, J.F. 2015 Diffusive dynamics and stochastic models of turbulent axisymmetric wakes. J. Fluid Mech. 778, R2.CrossRefGoogle Scholar
Shepherd, I.C. 1981 A four hole pressure probe for fluid flow measurements in three dimensions. Trans. ASME: J. Fluids Engng 103 (4), 590–594.Google Scholar
Varon, E., Aider, J.-L., Eulalie, Y., Edwige, S. & Gilotte, P. 2019 Adaptive control of the dynamics of a fully turbulent bimodal wake using real-time PIV. Exp. Fluids 60 (8), 124.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), 99.CrossRefGoogle Scholar
Wordley, S. & Saunders, J. 2008 On-road turbulence. SAE Intl J. Passenger Cars Mech. Syst. 1 (2008-01-0475), 341–360.CrossRefGoogle Scholar
Yan, G., Xia, C., Zhou, H., Zhu, H. & Yang, Z. 2019 Experimental investigation of the bi-stable behavior in the wake of a notchback MIRA model. Tech. Rep. SAE Technical Paper.CrossRefGoogle Scholar

Burton et al. supplementary movie 1

Bistable state switching of the square-back Ahmed body wake under low (~1%) turbulent flow conditions.

Download Burton et al. supplementary movie 1(Video)
Video 26.8 MB

Burton et al. supplementary movie 2

Bistable state switching of the square-back Ahmed body wake under high (13%) turbulent flow conditions.

Download Burton et al. supplementary movie 2(Video)
Video 30.8 MB