Study on the physical mechanisms of aerodynamic drag increase of road vehicle influenced by the adjacent vehicle

Key points of this research results

  • The aerodynamic effects of vehicles traveling in adjacent lanes were considered as one of typical conditions encountered in a real driving environment, and the causes of increase in aerodynamic drag of the vehicle due to these effects were clarified.
  • Three causes of increased aerodynamic drag were classified and the approximate evaluation of aerodynamic drag change based on the classification was quantitatively verified.
  • Applying the latest flow data mining technology for extracting "vortex structures" around the vehicle, we clarified the characteristic changes in the flow field due to the influence of vehicles traveling in the adjacent lane.


 In the conventional aerodynamic design and development of cars, performance evaluation has been carried out assuming ideal conditions where the vehicle is driven on a road with no wind, constant attitude and constant speed. Recently, however, the effects of various disturbances that occur during actual driving on the road have attracted increasing attention. One of the typical disturbances on a real road is the aerodynamic effect of vehicles travelling in the adjacent lane. Most studies on the aerodynamic effects of vehicles travelling in the adjacent lane have focused on the effects in terms of driving stability, and there have been few studies focusing on the change in aerodynamic drag.

 In this study, we focused on the influence of vehicles traveling in adjacent lanes and investigated the aerodynamic characteristics of vehicles under this influence and the aerodynamic phenomena that contribute to it. Wind tunnel experiments and numerical analysis of the flow were conducted to investigate the velocity and pressure fields around two simple vehicle models running in parallel, and the factors that increase drag were classified into three categories: "I. Influence of the pressure field around the vehicle in the adjacent lane," "II. Influence of the flow inclination around the vehicle in the adjacent lane," and "III. The other components due to aerodynamic interaction". The analysis results showed that the approximate evaluation by the two components (I. and II.) is roughly effective under general road conditions. Moreover, in order to clarify the physical mechanism that produces the additional component (III.), the latest flow data mining techniques that extract the "vortex core line" and the "streamlines forming the vortex" were applied. As a result, it was found that the influence of side vehicles changes vortices behind the vehicle, and that the change in vortices causes additional pressure decrease on the base of the vehicle.


Paper Info
Nakamura, Y., Nakashima, T., Shimizu, K., Hiraoka, T., Nouzawa, T., Kanehira T., and Mutsuda, H., Identification of wake vortices using a simplified automobile model under parallel running and crosswind conditions, Journal of Fluid Science and Technology, Vol. 18, No. 1 (2023), DOI: 10.1299/jfst.2023jfst0005.

Shimizu, K., Nakashima, T., Hiraoka, T., Nakamura, Y., Nouzawa, T., and Doi, Y., Aerodynamic drag change of simplified automobile models influenced by a passing vehicle, Mechanical Engineering Journal, Vol. 7, No. 1 (2020), DOI:10.1299/mej.19-00366.