Aerodynamics has such a profound impact on cycling performance at the elite level that it has infiltrated almost every aspect of the sport from riding position and styles, equipment design and selection, race tactics and training regimes, governing rules and regulations to even the design of new velodromes. This paper presents a review of the aspects of aerodynamics that are critical to understanding flows around cyclists under racing conditions, and the methods used to evaluate and improve aerodynamic performance at the elite level. The fundamental flow physics of bluff body aerodynamics and the mechanisms by which the aerodynamic forces are imparted on cyclists are described. Both experimental and numerical techniques used to investigate cycling aerodynamic performance and the constraints on implementing aerodynamic saving measures at the elite level are also discussed. The review reveals that the nature of cycling flow fields are complex and multi-faceted as a result of the highly three-dimensional and variable geometry of the human form, the unsteady racing environment flow field, and the non-linear interactions that are inherent to all cycling flows. Current findings in this field have and will continue to evolve the sport of elite cycling while also posing a multitude of potentially fruitful areas of research for further gains in cycling performance.

Three-dimensional flows around a full-scale cyclist mannequin were investigated experimentally to explain the large variations in aerodynamic drag that are measured as the legs are positioned around the 360 • crank cycle. It is found that the dominant mechanism affecting drag is not the small variation in frontal surface area over the pedal stroke but rather due to large changes in the flow structure over the crank cycle. This is clearly shown by a series of detailed velocity field wake surveys and skin friction flow visualizations. Two characteristic flow regimes are identified, corresponding to symmetrical low-drag and asymmetrical high-drag regimes, in which the primary feature of the wake is shown to be a large trailing streamwise vortex pair, orientated asymmetrically in the centre plane of the mannequin. These primary flow structures in the wake are the dominant mechanism driving the variation in drag throughout the pedal stroke. Topological critical points have been identified on the suction surfaces of the mannequin's back and are discussed with velocity field measurements to elucidate the time-average flow topologies, showing the primary flow structures of the low-and high-drag flow regimes. The proposed flow topologies are then related to the measured surface pressures acting on the suction surface of the mannequin's back. These measurements show that most of the variation in drag is due to changes in the pressure distribution acting on the lower back, where the large-scale flow structures having the greatest impact on drag develop.

An experimental and numerical analysis of cycling aerodynamics is presented. The cyclist is modeled experimentally by a mannequin at static crank angle; numerically, the cyclist is modeled using a computer aided design (CAD) reproduction of the geometry. Wind tunnel observation of the flow reveals a large variation of drag force and associated downstream flow structure with crank angle; at a crank angle of 15 deg, where the two thighs of the rider are aligned, a minimum in drag is observed. At a crank angle of 75 deg, where one leg is at full extension and the other is raised close to the torso, a maximum in drag is observed. Simulation of the flow using computational fluid dynamics (CFD) reproduces the observed variation of drag with crank angle, but underpredicts the experimental drag measurements by approximately 15%, probably at least partially due to simplification of the geometry of the cyclist and bicycle. Inspection of the wake flow for the two sets of results reveals a good match in the downstream flow structure. Numerical simulation also reveals the transient nature of the entire flow field in greater detail. In particular, it shows how the flow separates from the body of the cyclist, which can be related to changes in the overall drag.

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