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This work presents a detailed wind tunnel investigation into the nature of the unsteady flow mechanisms that dictate the aerodynamic forces acting on prime-mover trailer heavy vehicles fitted with various passive flow control devices. This work builds on the current understating of the wake flow physics of heavy vehicles that until now has primarily been developed from studies utilising highly simplified geometries or time-averaged findings with realistic geometries. Unsteady base-surface and wake pressure measurements reveal how the time-averaged and unsteady flow field responds to the addition of passive aerodynamic devices that have been shown to be effective on operational heavy vehicles for improving fuel economy and reducing emissions. In comparing turbulent wake statistics and unsteady modes the time-averaged and unsteady flow response is linked directly to the measured changes in the aerodynamic drag coefficient thorough surface pressure and force measurement. The large variation in the wake structure and dynamics observed between test configurations highlights the importance of considering the detailed geometry of heavy vehicles when looking to develop advanced aerodynamic control devices that would provide benefits above and beyond those focused on in this study. [ABSTRACT FROM AUTHOR]

In this wind-tunnel based experimental study, the flow topology of the near wake of a generic anatomically accurate model cyclist is mapped for a range of reduced pedalling frequencies. Wake flow fields for both static leg and pedalling cyclists are compared over the full 360° rotation of the crank using both time- and phase-averaging. The primary wake flow structures and aerodynamic forces are quantified and analysed under dynamic pedalling conditions representative of an elite-level time-trial cyclist. Over the range of reduced pedalling frequencies studied, only minor variation was detected between the instantaneous drag and primary vortical structures of a pedalling cyclist compared to a stationary cyclist with the pedals in the same position. A simplified model of the aerodynamic forces acting on the legs under motion is presented to provide insight into how the motion of the legs influences aerodynamic drag. A comparison of predicted forces from this model with those from experiments provides a new perspective on how the aerodynamics of cyclists may be optimised. [ABSTRACT FROM AUTHOR]

Many previous studies have focused on characterising Reynolds number effects and skinsuit design to better understand and improve aerodynamic performance. However, the majority of this research has been conducted in wind tunnels with turbulence intensities of less than 2%, considerably lower than that experienced when competing outdoors or in the wakes of competitors. In this systematic experimental study using passive turbulence generation, the influence of freestream turbulence on the aerodynamics of a cyclist is determined. Force measurements, wake velocity surveys, total pressure measurements and surface flow visualisations are used to characterise and quantify the aerodynamic behaviour. It is found that the aerodynamic drag is strongly affected by turbulence with it monotonically decreasing with increasing turbulence level. Moderate levels of turbulence are shown to alter local flow separation, and consequently the drag, on parts of the cyclist's body, which in turn is imprinted on the large-scale wake structures. The interaction of turbulence level and skinsuit roughness on the arms is also considered showing that these factors cannot be treated in isolation. Overall, this study highlights the importance of understanding the environment in which cyclists compete in order to optimise their performance. • The aerodynamic drag of a cyclist is highly sensitive to turbulence. • Turbulence alters local separation points of the geometry. • The development of the large-scale structures is affected by turbulence. • A smooth cyclist has lower aerodynamic drag than a skin suit in high turbulence. • Turbulence and Reynolds number have a similar effect on aerodynamic drag. [ABSTRACT FROM AUTHOR]