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

  • Angel Huminic
  • Gabriela Huminic


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 



reference area of the body, m2


aerodynamic coefficient


drag force, N


ride height, m


diffuser height, m


turbulence kinetic energy per unit mass, m2 s-2


lift, N


body length, m


diffuser length, m


pressure, Pa


second invariant of the velocity gradient tensor, s-2


Reynolds number


temperature, °C


velocity, m s-1


dimensionless wall coordinate

Greek symbol


diffuser angle, deg


deviation of CFD results from experiment, %


turbulence eddy dissipation, m2 s−3


density, kg m−3


turbulence eddy frequency, s−1


angular speed, s−1


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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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