The Drag Crisis Phenomenon on an Elite Road Cyclist—A Preliminary Numerical Simulations Analysis in the Aero Position at Different Speeds

• Main Authors: Pedro Forte, Jorge E. Morais, Henrique P. Neiva, Tiago M. Barbosa, Daniel A. Marinho
• Format: Article
• Language: English
• Published: MDPI AG 2020-07-01
• Series: International Journal of Environmental Research and Public Health
• Subjects: cycling; drag coefficient; drag crisis; numerical simulations
• Online Access: https://www.mdpi.com/1660-4601/17/14/5003
• ISSN: 1661-7827; 1660-4601

The drag crisis phenomenon is the drop of drag coefficient (C_d) with increasing Reynolds number (Re) or speed.<b> </b>The aim of this study was to assess the hypothetical drag crisis phenomenon in a sports setting, assessing it in a bicycle–cyclist system. A male elite-level cyclist was recruited for this research and his competition bicycle, helmet, suit, and shoes were used. A three-dimensional (3D) geometry was obtained with a 3D scan with the subject in a static aero position. A domain with 7 m of length, 2.5 m of width and 2.5 m of height was created around the cyclist. The domain was meshed with 42 million elements. Numerical simulations by computer fluid dynamics (CFD) fluent numerical code were conducted at speeds between 1 m/s and 22 m/s, with increments of 1 m/s. The drag coefficient ranged between 0.60 and 0.95 across different speeds and Re. The highest value was observed at 2 m/s (C_d = 0.95) and Re of 3.21 × 10⁵, whereas the lower C_d was noted at 9 m/s (C_d = 0.60) and 9.63 × 10⁵. A drag crisis was noted between 3 m/s and 9 m/s. Pressure C_d ranged from 0.35 to 0.52 and the lowest value was observed at 3m/s and the highest at 2 m/s. The viscous drag coefficient ranged between 0.15 and 0.43 and presented a trend decreasing from 4 m/s to 22 m/s. Coaches, cyclists, researchers, and support staff must consider that C_d varies with speed and Re, and the bicycle–cyclist dimensions, shape, or form may affect drag and performance estimations. As a conclusion, this preliminary work noted a drag crisis between 3 m/s and 9 m/s in a cyclist in the aero position.