Cyclist Drag Reduction through the Manipulation of the 3D Flow Topology

An investigation by means of numerical simulations and robotic volumetric PTV

Master thesis (2023)

Authors

H.M. van der Waals Aerospace Engineering

Contributors

A. Sciacchitano Aerodynamics - Aerospace Engineering (mentor)
W. Terra Innovation Affairs (graduation committee member)
Faculty
Aerospace Engineering, Aerospace Engineering
Copyright: © 2023 Max van der Waals
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Published Date

09-10-2023

Language

English

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Faculty

Aerospace Engineering

Abstract

The importance of aerodynamic efficiency in the cycling sport is well known. Simple calculations demonstrate the considerable impact of just a few percentages in drag savings on the outcome of a competition where the margins can be incredibly small. Achieving a drag reduction can, however, be challenging as the flow topology of a cyclist is extremely complex. Nonetheless, the manipulation of flow structures in other research areas is proven to be an effective method for reducing aerodynamic resistance. Hence, the potential of achieving a drag reduction for a cyclist in a time trial position through the manipulation of the 3D flow topology is investigated.

Two devices are introduced named the Hip Vortex Control (HVC) and wingsuit aiming to reduce the streamwise vorticity at the hips and upper arms respectively. A reduction of a crosswind-dependent weighted drag area of -1.35% for the HVC and -5.45% for the wingsuit is measured experimentally. Computational Fluid Dynamics (CFD) simulations and robotic volumetric Particle Tracking Velocimetry (PTV) provide the trends in the drag-reducing mechanisms. The HVC promotes separation on the lower back of the cyclist, reducing the presence of the hip vortices leading to an increase of the pressure on the lower back. The wingsuit limits the formation of the streamwise vortices around the upper arms, slightly increasing the wake and increasing the pressure on the upper arms resulting in the drag reduction.

The numerical and experimental results largely agree on the variations in the flow topology for each configuration. The results indicate that a reduction in streamwise vorticity in the wake of a bluff body can reduce the drag considerably. Both devices lead to an expansion of the wake which should be kept to a minimum to effectively reduce the drag. The results motivate the continuation of the research into the reduction of streamwise vortices in the development of cycling equipment and in other high-velocity sports.