The effects of surface roughness on the aerodynamic drag coefficient of vehicles

In this study, the effects of surface roughness differences of vehicle coating ma-terials (paint, paste, special applications, etc.) on the aerodynamic drag coefficient were investigated using the finite element method. For this, aerodynamic drag forc-es and aerodynamic drag coefficients for speeds between 40-150 km/hours were calculated for a 1/20 scale vehicle designed by a package program by defining the body parts and front-rear window parts separately and assigning pre-calculated roughness values suitable in the industry, and the results were presented through graphs and visuals. Using three different paint roughness values (low, medium, and high), and one commonly used Teflon (fluoropolymer) coating, it was observed that the aerodynamic resistance coefficient increased with increasing roughness levels. Relative to the aerodynamic resistance coefficient for the lowest paint roughness value, the aerodynamic resistance coefficient for the medium roughness value showed an increase of 0.000612529%, the aerodynamic resistance coeffi-cient for the high roughness value showed an increase of 0.00104783%, and the aerodynamic resistance coefficient for the fluoropolymer coating showed an in-crease of 0.091195826%. In addition, the distribution of the pressure forces on the vehicle hood and windscreen were also observed in the study. It was observed that the pressure forces, which were approaching maximum on the front bumper, wind-screen and side mirrors, were reduced over the rear windscreen area due to separat-ed flow. It was also observed that the aerodynamic resistance force can be reduced by processes such as angular improvements to be made in the front bumper and vehicle windscreens.