Aerodynamic benefits for a cyclist by drafting behind a motorcycle
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ORIGINAL ARTICLE
Aerodynamic benefits for a cyclist by drafting behind a motorcycle Bert Blocken1,2 · Fabio Malizia1,2 · Thijs van Druenen1 · Stefanie Gillmeier1
© The Author(s) 2020
Abstract Motorcycles are present in cycling races for reasons including television broadcasting. During parts of the race, these motorcycles ride in front of individual or groups of cyclists. Concerns have been expressed in the professional cycling community that these motorcycles can provide aerodynamic benefits in terms of drag reduction for the cyclists drafting behind them. However, to the best of our knowledge, no information about the extent of these benefits is present in the scientific literature. Therefore, this paper analyses the potential drag reduction for a cyclist by drafting behind a motorcycle. Wind tunnel measurements and numerical simulations with computational fluid dynamics were performed. It was shown that drafting at separation distances d = 2.64, 10, 30 and 50 m can reduce the drag of the cyclist down to 52, 77, 88 and 93% of that of an isolated cyclist, respectively. A cyclist power model is used to convert these drag reductions into potential time gains. For a non-drafting cyclist at a speed of 54 km/h on level road in calm weather, the time gains by drafting at d = 2.64, 10, 30 and 50 m are 12.7, 5.4, 2.7 and 1.6 s per km, respectively. These time differences can influence the outcome of cycling races. The current rules of the International Cycling Union do not prevent these aerodynamic benefits from occurring in races. Keywords Computational fluid dynamics · Wind tunnel · Aerodynamic cyclist drag · Cycling aerodynamics · motorbike
1 Introduction At racing speeds of about 40 km/h, the aerodynamic resistance or drag of a cyclist is about 90% of the total resistance [1–3]. Therefore many efforts in professional cycling and in cycling research are focused on the reduction of the cyclist’s drag. Especially in the past two decades, scientific research in cycling aerodynamics has rapidly increased as reported in recent review papers [4, 5]. Recent research has focused on the factors determining the aerodynamic resistance, including different cyclist positions (e.g. [6–11]) and the associated flow topologies [12–14], the bicycle and bicycle components Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12283-020-00332-z) contains supplementary material, which is available to authorized users. * Bert Blocken [email protected] 1
Building Physics and Services, Department of the Built Environment, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
Building Physics Section, Department of Civil Engineering, KU Leuven, Kasteelpark Arenberg 40, Bus 2447, 3001 Leuven, Belgium
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[5, 15–17], wearable equipment such as helmets (e.g. [18, 19]) and the interaction between drafting cyclists [20–25]. Together with previous studies, these efforts have led to more and better insights in the aerodynamics of cycling. Less attention howev
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