Characterisation of Wake Bi-stability for a Square-Back Geometry with Rotating Wheels
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. ) are investigated considering a modified version of the Windsor body already studied in Perry et al. . 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.  for the same geometry without wheels.
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.
- 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.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
- 6.Duell, E.G., George, A.: Experimental study of a ground vehicle body unsteady near wake. Technical report, SAE technical paper (1999)Google Scholar
- 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
- 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
- 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.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
- 20.SAE: Surface vehicle recommended practice. Technical report J1594. SAE International (2010)Google Scholar
- 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
- 25.Wood, D.: The effect of rear geometry changes on the notchback flow field. Ph.D. thesis, ©Daniel Wood (2015)Google Scholar