Bert Blocken

At racing speeds and over level terrain, the greatest potential for improvement in cycling speed is situated in its aerodynamics ( Grappe et al. , 1997 ; Kyle and Burke, 1984 ; Lukes et al. , 2005 ; Wilson, 2004 ). The greatest potential for improvement in such cases is situated in group riding, also called drafting. This chapter first discusses drafting by riding in a single paceline to riding in a peloton. Next, it focuses on breakaways, and it outlines a mathematical model to time the optimal breakaway. The chapter concludes with some directions for future research and innovation.

Aerodynamic modifications present substantial opportunities for enhancing cycling speed ( Wilson, 2004 ). This chapter reviews the historical recognition of aerodynamics as a critical determinant of cycling performance, beginning shortly after the bicycle's invention. The relationship between aerodynamic drag and the various forces influencing a cyclist's motion is examined to provide a comprehensive framework for understanding overall performance. A primary determinant of aerodynamic efficiency is rider position, underscoring the significance of optimal bike fitting. Achieving a balance among aerodynamic benefits, rider power output, and comfort is essential. Furthermore, equipment such as clothing and helmets contributes meaningfully to aerodynamic outcomes. Methods for evaluating aerodynamic performance are discussed, including field testing, wind tunnel (WT) measurements, and computational fluid dynamics (CFD) simulations. Each approach offers unique insights and practical implications for performance refinement. Emerging trends anticipate further individualisation of equipment and highlight the dynamic interaction between regulations, such as those imposed by the Union Cycliste Internationale (UCI) and ongoing advancements in design innovation and performance optimisation.

Hazardous pollutant containment zones should be maintained at a pressure lower than the outdoor atmospheric pressure to prevent pollutants from escaping to the outdoor environment. However, atmospheric wind conditions can cause breaching of the containment zone that is established through mechanical ventilation. This paper combines external wind pressure (Pe) time series on an internally depressurized building with a carefully designed ventilation network to analyze indoor pressure (Pi) and containment breach duration. The Pe data are obtained by wind-tunnel (WT) tests and computational fluid dynamics (CFD) simulations of large-eddy simulation (LES) and scale-adaptive simulation (SAS). The objectives of the paper are (1) comparing Pe results by WT and CFD; (2) assessing the impact of Pe uncertainties in CFD on the resulting Pi and breach duration; and (3) estimating Pi and breach duration for an initial case study with indoor depressurization of -40 Pa and reference wind speed (Uref) of 12.65 m/s at building height. The results are discussed in terms of dimensionless pressure coefficients (Cpe and Cpi). It is shown that LES and especially SAS Cpe data deviate substantially from the WT values but that the impact of these CFD uncertainties on Cpi and breach duration remains fairly limited. Deviations for Cpi statistics fall within the experimental uncertainty, and the CFD breach duration deviates generally less than 10% from the WT result. Estimated breach durations for Uref = 12.65 m/s, however, can go up to 80% in spite of the −40 Pa depressurization, stressing the importance of this type of studies.