Titel Deelnemers "Impact of a nearby car on the drag of a cyclist" "Bert Blocken, Fabio Malizia" "Impact of Disc Wheel Geometry on Aerodynamic Performance: A Computational Fluid Dynamics Investigation" "Fabio Malizia, Bert Blocken" "Cyclist aerodynamics through time: Better, faster, stronger" "Fabio Malizia, Bert Blocken" "Impact of a motorcycle on cyclist aerodynamic drag in parallel and staggered arrangements" "Bert Blocken, Fabio Malizia" "Impact of wheel rotation on the aerodynamic drag of a time trial cyclist" "Fabio Malizia, Bert Blocken" "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." "Aerodynamic benefits for a cyclist by drafting behind a motorcycle" "Bert Blocken, Fabio Malizia" "Modeling of Wheel Aerodynamics and its Impact on Cycling" "Fabio Malizia" "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." "CFD simulations of an isolated cycling spoked wheel: The impact of wheel/ground contact modeling in crosswind conditions" "Fabio Malizia, Bert Blocken" "Bicycle aerodynamics: History, state-of-the-art and future perspectives" "Fabio Malizia, Bert Blocken" "CFD simulations of an isolated cycling spoked wheel: Impact of the ground and wheel/ground contact modeling" "Fabio Malizia, Bert Blocken" "Spoked wheels are the most frequently used wheel type in road cycling competitions and their aerodynamic optimization is crucial for cyclist performance. The aerodynamic performance of wheels is generally analyzed by wind tunnel tests or CFD simulations for isolated wheels. There is a large number of options to model the wheel/ground contact in CFD simulations, including different clearances between tire and ground and different heights of solid contact patches (step). However, it is unclear to what extent these modeling options influence the CFD results. The present paper systematically analyzes the impact of these options on the computed forces and moments of an isolated cycling spoked wheel and elucidates the flow behavior around this wheel for zero yaw conditions. The wheel drag coefficient for the cases where the ground is included in the simulations using a clearance or a step is 1.0% and about 1.8% lower compared to the case without ground, respectively, whereas the rotational moment is about 2.0% lower for all the wheel/ground contact modeling approaches compared to the case without ground. The gap clearance (≤20 mm) and step height (≤10 mm) should be kept minimal to avoid a significant influence on the forces and moments. In addition, the presence of the ground influences the flow behavior in the lower section of the wheel including the pressure distribution on the exterior of the wheel. This study is intended to help researchers and manufacturers to perform accurate CFD simulations of cycling spoked wheels and to optimize their aerodynamics."