< Terug naar vorige pagina

Publicatie

Modeling of Wheel Aerodynamics and its Impact on Cycling

Boek - Dissertatie

Aerodynamic resistance is a core focus in cycling as it is responsible for about 90% of the total resistance at speeds larger than 40 km/h on flat terrain. The aerodynamic performance of both wheels is a critical factor in the overall cycling performance, as the wheels can be responsible for up to about 10% of the total cyclist-bicycle drag, and races can be decided by very small time differences. Past research on cycling wheel aerodynamics mainly focused on the aerodynamic comparison of different types of wheels. However, large discrepancies in terms of set-up and drag force result have been reported between different studies, either when performing wind tunnel tests (WT) or computational fluid dynamics simulations (CFD). These discrepancies raise serious concerns and inhibit confidence in the current testing and simulation methods. The reduced confidence in CFD simulations needs to be tackled by means of a rigorous and systematic assessment of the impact of the main computational parameters and of the physical parameters on the cycling wheel aerodynamics.Therefore, the main goal of this dissertation is to perform an analysis of cycling aerodynamics focused on wheel aerodynamics. The primary research tool used is CFD simulation, the results of which are validated with WT experiments available in the literature or performed in-house. In order to achieve this main goal, the first subobjective is to perform an extensive literature review on the current practice in testing and simulation methods for cycling in general and for wheel aerodynamics in particular. Therefore it is necessary to establish a solid framework to perform accurate and reliable CFD simulations of cycling wheels, so that the aerodynamics of different wheels can be compared both when the wheels are considered isolated from the rest of the bicycle and when the wheels are considered together with the bicycle. The second subobjective is to establish best practice guidelines for the CFD modeling of isolated wheel aerodynamics based on a systematic sensitivity analysis. The third and last subobjective is to compare the aerodynamics of isolated and non-isolated spoked wheels, both in static and rotating conditions.The first part of the dissertation provides a comprehensive review of the history and the state-of-the-art in cycling aerodynamics, focusing both on the aerodynamics of the bicycle and the cyclist/s. It confirms the strong lack of consistency and the lack of confidence in the current practice in testing and simulation methods for cycling wheel aerodynamics. The second part of the dissertation investigates how the computational parameters - grid discretization, wheel rotation modeling, turbulence modeling - influence the aerodynamic results of a cycling spoked wheel. Guidelines about the grid topology and resolution on a cycling spoked wheel are provided. In addition the k-ω SST, γSST and Standard k-ε with enhanced wall treatment turbulence models are suggested when the hybrid MRF-RW rotational approach is used to model the wheel rotation, whereas the k-ω SST turbulence model should be used when using the MRF approach to model the wheel rotation. Moreover, the impact of the presence or lack of the ground in CFD simulations of cycling wheels is assessed. The impact of the wheel/ground contact modeling with and without crosswind on the wheel aerodynamics is quantified, both when the wheel is displaced from the ground - suggested max distance ≤ 10 mm or 20 mm with and without crosswind, respectively - and when a step replaces the contact patch between the wheel and the ground - suggested max height ≤ 10 mm. In the third and last part of the dissertation, the wheel is considered both isolated and not isolated from the rest of the bicycle and cyclist, and differences in these two investigation approaches are highlighted.The results and guidelines developed in this PhD dissertation will help researchers and manufacturers to perform accurate CFD simulations of wheels, isolated or combined with the rest of the bicycle and cyclist, enabling them to assess and further optimize the wheel aerodynamics and thus the cyclist performance.
Jaar van publicatie:2020