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Aerodynamic study of a generic car model with wheels and underbody diffuser

  • Angel Huminic
  • Gabriela Huminic
Article
  • 368 Downloads

Abstract

Being a continuous subject of research, this study presents new aspects regarding the relevance of underbody diffusers in road vehicle aerodynamics. Using a generic car model on wheels as a reference, the effect of the wheels on the body fitted with an underbody diffuser was studied, where the diffuser length and angle were varied within ranges which are applicable for hatchback passenger cars. The results show that the vortices which originate from the rear wheelhouses have a major impact on the aerodynamics of the underbody diffuser, which results in increasing of drag and lift of the body. For cases studied, the average drag and lift increment due to the addition of wheels were (ΔcD)mean = 0.058, respectively (ΔcL)mean = 0.243. The lift of the body on wheels decreases with both diffuser length and diffuser angle, and there are situations when it may become negative as for a body without wheels. The results show also the possibility to reach a minimum drag according with normalised diffuser length.

Key words

Automobile Underbody diffuser Aerodynamics 

Nomenclature

A

reference area of the body, m2

C

aerodynamic coefficient

D

drag force, N

h

ride height, m

hd

diffuser height, m

k

turbulence kinetic energy per unit mass, m2 s-2

L

lift, N

l

body length, m

ld

diffuser length, m

p

pressure, Pa

Q

second invariant of the velocity gradient tensor, s-2

Re

Reynolds number

t

temperature, °C

v

velocity, m s-1

y+

dimensionless wall coordinate

Greek symbol

α

diffuser angle, deg

δ

deviation of CFD results from experiment, %

ε

turbulence eddy dissipation, m2 s−3

ρ

density, kg m−3

ω

turbulence eddy frequency, s−1

ω

angular speed, s−1

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References

  1. Ahmed, S., Ramm, G. and Faltin, G. (1984). Some salient features of the time-averaged ground vehicle wake. SAE Paper No. 840300.Google Scholar
  2. Breslouer, J. O. and George, A. R. (2008). Exploratory experimental studies of forces and flow structure on a bluff body with variable diffuser and wheel configurations. SAE Paper No. 2008-01-0326.Google Scholar
  3. Cogotti, A. (1983). Aerodynamic Characteristics of Car Wheels. Technological Advances in Vehicle Design Series, SP3, Impact of Aerodynamics on Vehicle Design, 173–196.Google Scholar
  4. Conan, B., Anthoine, J. and Planquart, P. (2011). Experimental aerodynamic study of a car-type bluff body. J. Experiments on Fluids 50, 5, 1273–1284.CrossRefGoogle Scholar
  5. Cooper, K. R., Bertenyi, T., Dutil, G., Syms, J. and Sovran, G. (1998). The aerodynamic performance of automotive underbody diffusers. SAE Paper No. 980030.Google Scholar
  6. Cooper, K. R., Sovran, G. and Syms, J. (2000). Selecting automotive diffusers to maximise underbody downforce. SAE Paper No. 2000-01-0354.Google Scholar
  7. Desai, S., Lo, C. M. and George, A. R. (2008). A computational study of idealized bluff bodies, wheels, and vortex structures in ground effect. SAE Paper No. 2008-01-0327.Google Scholar
  8. Fabijanic, J. (1996). An experimental investigation on wheel-well flows. SAE Paper No. 960901.Google Scholar
  9. Hetherington, B. and Sims-Williams, D. (2006). Support strut interference effects on passenger and racing car wind tunnel models. SAE Paper No. 2006-01-0565.Google Scholar
  10. Howell, J. P. (1994). The influence of a vehicle underbody on aerodynamics of a simple car shapes with an underfloor diffuser. Vehicle Aerodynamics R.Ae.S. Conf., Loughborough, UK.Google Scholar
  11. Huminic, A. and Huminic, G. (2010). Computational study of flow in the underbody diffuser for a simplified car model. SAE Paper No. 2010-01-0119.Google Scholar
  12. Huminic, A. and Huminic, G. (2012). Numerical flow simulation for a generic vehicle body on wheels with variable underbody diffuser. SAE Paper No. 2012-01-0172.Google Scholar
  13. Huminic, A., Huminic, G. and Soica, A. (2012). Study of aerodynamics for a simplified car model with the underbody shaped as a Venturi nozzle. Int. J. Vehicle Design 58, 1, 15–32.CrossRefGoogle Scholar
  14. Jeong, J. and Hussain, F. (1995). On the identification of a vortex. J. Fluid Mechanics, 285, 69–94.MathSciNetCrossRefzbMATHGoogle Scholar
  15. Jowsey, L. and Passmore, M. (2010). Experimental study of multiple-channel automotive underbody diffusers. Proc. Institution of Mechanical Engineers, Part D: J. Automobile Engineering 224, 7, 865–879.Google Scholar
  16. Katz, J. (2006). Race Car Aerodynamics -Designing for Speed. 2nd edn. Bentley Publisher. Cambridge, Massachusetts, USA.Google Scholar
  17. Launder, B. E. and Spalding, D. B. (1974). The numerical computation of turbulent flows. Computer Methods in Applied Mechanics and Engineering 3, 2, 269–289.CrossRefzbMATHGoogle Scholar
  18. Le Good, M. G. and Garry, P. K. (2004). On the use of reference models in automotive aerodynamics. SAE Paper No. 2004-01-1308.Google Scholar
  19. Menter, F. R. (1994). Two-equation eddy-viscosity turbulence models for engineering applications. AIAA J. 32, 8, 1598–1605.CrossRefGoogle Scholar
  20. Regert, T. and Lajos, T. (2007). Description of flow field in the wheelhouses of cars. Int. J. Heat and Fluid Flow 28, 4, 616–629.CrossRefGoogle Scholar
  21. Ruhrmann, A. and Zhang, X. (2003). Influence of diffuser angle on a bluff body in ground effect. J. Fluids Engineering 125, 2, 332–338.CrossRefGoogle Scholar
  22. SAE (1993). Aerodynamic Testing of Road Vehicle -Testing Methods and Procedures. SAE Information Report SAE J2084 JAN93.Google Scholar
  23. Senior, A. E. and Zhang, X. (2001). The force and pressure of a diffuser-equipped bluff body in ground effect. J. Fluids Engineering 123, 1, 105–111.CrossRefGoogle Scholar
  24. Song, K. S., Kang, S. O., Jun, S. O., Park, H. I., Kee, J. D., Kim, K. H. and Lee, D. H. (2012). Aerodynamic design optimization of rear body shapes of a sedan for drag reduction. Int. J. Automotive Technology 13, 6, 905–914.CrossRefGoogle Scholar
  25. Strachan, R., Knowles, K. and Lawson, N. (2007). The vortex structure behind an Ahmed reference model in the presence of a moving ground plane. J. Experiments on Fluids 42, 5, 659–669.CrossRefGoogle Scholar
  26. Wilcox, D. C. (1986). Multiscale model for turbulent flows. AIAA J. 26, 11, 1311–1320.MathSciNetCrossRefGoogle Scholar

Copyright information

© The Korean Society of Automotive Engineers and Springer-Verlag Berlin Heidelberg 2017

Authors and Affiliations

  1. 1.Aerodynamics LaboratoryTransilvania University of BrasovBrasovRomania

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