Advertisement

Characterisation of Wake Bi-stability for a Square-Back Geometry with Rotating Wheels

  • Giancarlo Pavia
  • Martin Passmore
Conference paper

Abstract

In this paper the effects produced by the wheels on the bi-stable reflectional symmetry breaking (RSB) mode seen for the wake of a square-back geometry (Grandemange et al. [11]) are investigated considering a modified version of the Windsor body already studied in Perry et al.  [18]. The contribution of the wheels and their rotation to the changes in the base pressure distribution and the wake topology is characterised by means of pressure tappings and 2D-3C particle image velocimetry. Balance measurements are used to further characterise the changes in the strength of the RSB mode. For the pure square-back configuration, the results show a general increase of the base drag as a consequence of the strengthening of the suction over the lower portion of base, due to the formation of a pair of counter rotating vortices acting close to the bottom trailing edge. At the same time, the RSB mode is weakened, leading to a reduction in the fluctuations recorded for the lateral component of the aerodynamic force. The sensitivity of the RSB mode to small changes in the shape of the model’s trailing edges is characterised by looking at the effects produced by short tapers, with a slant angle of 12° and a chord equal to 4% of the model length, applied to either the horizontal or the vertical trailing edges. The results show that the RSB mode disappears when the effect of the wheels is paired to the upwash generated by the slanted surface (when applied to the bottom trailing edge), although it is still clearly visible when the tapers are applied to the side edges of the base, in contrast with the results reported by Pavia et al. [16] for the same geometry without wheels.

Notes

Acknowledgements

The authors would like to thank Jaguar Land Rover for the financial support. Thanks are also due to Mr. David Cooper and Mr. Nigel Lines for their excellent work in manufacturing the models and keeping the test facility always in optimal conditions.

References

  1. 1.
    Ahmed, S., Ramm, G., and Faitin, G.: Some salient features of the time-averaged ground vehicle wake. Technical report, Society of Automotive Engineers, Inc., Warrendale, PA (1984)Google Scholar
  2. 2.
    Barros, D.: Wake and drag manipulation of a bluff body using fluidic forcing. Ph.D. thesis, École Nationale Supérieure de Mécanique et de Aérotechnique (ENSMA) (2015)Google Scholar
  3. 3.
    Benedict, L., Gould, R.: Towards better uncertainty estimates for turbulence statistics. Exp. Fluids 22(2), 129–136 (1996)CrossRefGoogle Scholar
  4. 4.
    Bonnavion, G., Cadot, O., Évrard, A., Herbert, V., Parpais, S., Vigneron, R., Délery, J.: On multistabilities of real car’s wake. J. Wind Eng. Ind. Aerodyn. 164, 22–33 (2017)CrossRefGoogle Scholar
  5. 5.
    Brackston, R., de la Cruz, J.G., Wynn, A., Rigas, G., Morrison, J.: Stochastic modelling and feedback control of bistability in a turbulent bluff body wake. J. Fluid Mech. 802, 726–749 (2016)MathSciNetCrossRefGoogle Scholar
  6. 6.
    Duell, E.G., George, A.: Experimental study of a ground vehicle body unsteady near wake. Technical report, SAE technical paper (1999)Google Scholar
  7. 7.
    Evrard, A., Cadot, O., Herbert, V., Ricot, D., Vigneron, R., Délery, J.: Fluid force and symmetry breaking modes of a 3d bluff body with a base cavity. J. Fluids Struct. 61, 99–114 (2016)CrossRefGoogle Scholar
  8. 8.
    Grandemange, M.: Analysis and control of three-dimensional turbulent wakes: from axisymmetric bodies to road vehicles. Ph.D. thesis, Palaiseau, Ecole polytechnique (2013)Google Scholar
  9. 9.
    Grandemange, M., Cadot, O., Courbois, A., Herbert, V., Ricot, D., Ruiz, T., Vigneron, R.: A study of wake effects on the drag of Ahmed’s squareback model at the industrial scale. J. Wind Eng. Ind. Aerodyn. 145, 282–291 (2015)CrossRefGoogle Scholar
  10. 10.
    Grandemange, M., Gohlke, M., Cadot, O.: Bi-stability in the turbulent wake past parallelepiped bodies with various aspect ratios and wall effects. Phys. Fluids (1994-Present) 25(9), 95–103 (2013)zbMATHGoogle Scholar
  11. 11.
    Grandemange, M., Gohlke, M., Cadot, O.: Turbulent wake past a three-dimensional blunt body. Part 1: global modes and bi-stability. J. Fluid Mech. 722, 51–84 (2013)CrossRefGoogle Scholar
  12. 12.
    Grandemange, M., Gohlke, M., Cadot, O.: Turbulent wake past a three-dimensional blunt body. Part 2: experimental sensitivity analysis. J. Fluid Mech. 752, 439–461 (2014)CrossRefGoogle Scholar
  13. 13.
    Johl, G.: The design and performance of a 1.9 m × 1.3 m indraft wind tunnel. Ph.D. thesis, Ⓒ Guru Johl (2010)Google Scholar
  14. 14.
    Krajnovic, S., Davidson, L.: Numerical study of the flow around a bus-shaped body. J. Fluids Eng. 125(3), 500–509 (2003)CrossRefGoogle Scholar
  15. 15.
    Makihara, T., Kitamura, T., Yamashita, T., Maeda, K., Kato, C., Takayama, T., Yamamoto, K., Yamade, Y., Suzuki, Y.: Identification of vortical structure that drastically worsens aerodynamic drag on a 2-box vehicle using large-scale simulations. SAE Int. J. Passeng. Cars-Mech. Syst. 9, 592–602 (2016). 2016-01-1585CrossRefGoogle Scholar
  16. 16.
    Pavia, G., Passmore, M., Gaylard, A.: Influence of short rear end tapers on the unsteady base pressure of a simplified ground vehicle. Technical report, SAE technical paper (2016)Google Scholar
  17. 17.
    Perry, A.-K., Almond, M., Passmore, M., Littlewood, R.: The study of a bi-stable wake region of a generic squareback vehicle using tomographic piv. SAE Int. J. Passeng. Cars-Mech. Syst. 9 ,743–754 (2016). 2016-01-1610CrossRefGoogle Scholar
  18. 18.
    Perry, A.-K., Pavia, G., Passmore, M.: 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 (2016)CrossRefGoogle Scholar
  19. 19.
    Prasad, A.K.: Stereoscopic particle image velocimetry. Exp. Fluids 29(2), 103–116 (2000)CrossRefGoogle Scholar
  20. 20.
    SAE: Surface vehicle recommended practice. Technical report J1594. SAE International (2010)Google Scholar
  21. 21.
    Sims-Williams, D.B., Dominy, R.: Experimental investigation into unsteadiness and instability in passenger car aerodynamics. Technical report, SAE technical paper (1998)Google Scholar
  22. 22.
    Varon, E., Eulalie, Y., Edwige, S., Gilotte, P., Aider, J.-L.: Chaotic dynamics of large-scale structures in a turbulent wake. Phys. Rev. Fluids 2(3), 034604 (2017)CrossRefGoogle Scholar
  23. 23.
    Volpe, R., Devinant, P., Kourta, A.: 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 (2015)CrossRefGoogle Scholar
  24. 24.
    Willert, C.E., Gharib, M.: Digital particle image velocimetry. Exp. Fluids 10(4), 181–193 (1991)CrossRefGoogle Scholar
  25. 25.
    Wood, D.: The effect of rear geometry changes on the notchback flow field. Ph.D. thesis, ©Daniel Wood (2015)Google Scholar

Copyright information

© Springer International Publishing AG 2018

Authors and Affiliations

  1. 1.Loughborough UniversityLoughboroughUK

Personalised recommendations