Improving CFD prediction of drag on Paralympic tandem athletes: influence of grid resolution and turbulence model

Fighting crosswinds in cycling: A matter of aerodynamics

OBJECTIVES

The main goal of this study was to compare the aerodynamic optimization level in echelon-formation strategy for riders fighting against a crosswind from the best (echelon or diagonal paceline) to the worst riders' configuration (guttered riders).

DESIGN

The case reported herein concerned a group of 5 cyclists riding at 30 km/h with a 30 km/h crosswind oriented at 40° to the direction of travel. The effects of the wind, expressed in terms of aerodynamic resistance or pressure, were determined for each cyclist in the different configurations.

METHODS

The 3D numerical simulations were performed using a calculation code based on the finite volume method and the Reynolds-averaged Navier-Stokes turbulence model k-kl-ω.

RESULTS

The results showed that the lateral force savings, averaged over the whole five-riders group, ranged from 50% in the echelon-optimized configuration to 11% in the guttered straight-line one, compared to a solo rider in the same velocity and windy conditions. Individually, the rider with the best aerodynamic shelter is the 4th rider in the "4 rider echelon + 1 guttered rider" formation (- 53.6% in drag force and - 69.8% in lateral force), while the rider with the worst aerodynamic situation is the leader of the straight paceline (- 0.1% in drag force and - 0.2% in lateral force).

CONCLUSIONS

The analysis showed how the spatial management of riders significantly influences drag and lateral forces and supported the idea that avoiding being guttered is the best way to save energy in windy races.

Time-Trial Performance of Para-Cycling Athletes With Visual Impairment in Tandem Competitions: A Retrospective Analysis of 20 Yrs

ABSTRACT

Identifying performance variables associated with visual impairment classification in para-cycling is one of the steps to improve the evidence-based classification system, and consequently, bring equality in Paralympic sports. Thus, this retrospective study aimed to analyze a 1-km tandem-track race performance among para-cyclists (male and female) with different visual impairment degrees (B1, B2, and B3) and to verify the retrospective performance over 20 yrs in all sport classes. The data were extracted from 427 para-cyclists (251 male and 176 female) who competed in the Para-Cycling World Championships and Paralympic Games. The following performance variables were analyzed: time trial, velocity, pace strategies, and number of medals. A one-way analysis of variance was used to compare performance variables among athletes of different sport classes (B1, B2, and B3) and χ2 tests were implemented to test the association between sport classes and medal distribution with a level of significance set at a P value of less than 0.05. The main results revealed that partially sighted athletes exhibited better tandem-track race performance compared with blind athletes (P < 0.05). Significant associations between sport classes and medal distribution in male (P = 0.026) and female (P = 0.017) athletes were found (higher in B3 athletes). Only 23.2% of male and 41.5% of female B3 athletes were medalists, and B3 athletes performed better specifically compared with B1 in most race distances. Finally, B2 and B3 athletes showed higher performance improvements than B1 throughout 20 yrs in the male group. It was concluded that male and female visual impairment athletes who classified as B1 displayed lower tandem-track race performance and medal frequency compared with partially sighted athletes, mainly considering those in the B3 class. The competitive system for athletes with visual impairment should be improved to provide more equity in the track para-cycling events.

Aerodynamic analysis of uphill drafting in cycling

Some teams aiming for victory in a mountain stage in cycling take control in the uphill sections of the stage. While drafting, the team imposes a high speed at the front of the peloton defending their team leader from opponent’s attacks. Drafting is a well-known strategy on flat or descending sections and has been studied before in this context. However, there are no systematic and extensive studies in the scientific literature on the aerodynamic effect of uphill drafting. Some studies even suggested that for gradients above 7.2% the speeds drop to 17 km/h and the air resistance can be neglected. In this paper, uphill drafting is analyzed and quantified by means of drag reductions and power reductions obtained by computational fluid dynamics simulations validated with wind tunnel measurements. It is shown that even for gradients above 7.2%, drafting can yield substantial benefits. Drafting allows cyclists to save over 7% of power on a slope of 7.5% at a speed of 6 m/s. At a speed of 8 m/s, this reduction can exceed 16%. Sensitivity analyses indicate that significant power savings can be achieved, also with varying bicycle, cyclist, road and environmental characteristics.

Impact of wheel rotation on the aerodynamic drag of a time trial cyclist

Aerodynamic drag is the main resistive force in cycling at high speeds and on flat terrain. In wind tunnel tests or computational fluid dynamics simulations, the aerodynamic drag of cycling wheels is often investigated isolated from the rest of the bicycle, and sometimes in static rather than rotating conditions. It is not yet clear how these testing and simulating conditions influence the wheel aerodynamic performance and how the inclusion of wheel rotation influences the overall measured or computed cyclist drag. This study presents computational fluid dynamics simulations, validated with wind tunnel tests, that indicate that an isolated static spoked front wheel has a 2.2% larger drag area than the same wheel when rotating, and that a non-isolated static spoked front wheel has a 7.1% larger drag area than its rotating counterpart. However, rotating wheels are also subjected to the rotational moment, which increases the total power required to rotate and translate the wheel compared to static conditions where only translation is considered. The interaction with the bicycle frame and forks lowers the drag area of the front wheel by 8.8% for static and by 12.9% for the rotating condition, compared to the drag area of the isolated wheels. A different flow behavior is also found for static versus rotating wheels: large low-pressure regions develop from the hub for rotating wheels, together with a lower streamwise velocity region inside the circumference of the wheel compared to static wheels. The results are intended to help in the selection of testing/simulating methodologies for cycling spoked wheels.