Numerical study of bicycle racing wheels aerodynamic performances

Improving the aerodynamic performance in one of the major challenges in the engineering research applied to racing bicycle. In fact, aerodynamic drag is the main source of losses in cycling and causes between 70% and 90% of total losses in flat road pace (i.e., when not climbing). Moreover, also lateral forces imposed by crosswinds play an important role because they can destabilize the bike itself. The body of the cyclist is actually the most important source of drag, because of its relevant frontal area. However, it is necessary to improve also the bike’s components aerodynamics, which account for about the 33% of the total drag. This quite relevant percentage is mainly due to the wheels and the frame design. According to Greenwell, wheel drag is responsible for 10% to 15% of total aerodynamic drag; therefore improving the design of this component can reduce the resistance of the bicycle by 2-3%. These numbers, in view of the high level required by either the today’s competitions or the bicycle market justify the effort involved in cycling components aerodynamics. The aim of this work isto assess the capability of CFD RANS simulations to predict the aerodynamic performance of modern racing bicycle wheels, and therefore build a numerical testing method to help the comparison between different solution and design. The Thesis is subdivided in five chapters after an introduction to bicycle aerodynamics and a literature review of the previous literature regarding the wheel aerodynamics; we give a look at the theory regarding the computational fluid dynamics and the different model used in this work. An initial method is build tested validated and refined showing the capabilities of the CFD to resolve the aerodynamic forces on a rotating wheel using a simpler steady-state analysis, applying the MRF method imposing a rotating frame to the region containing the wheel. Different wheels were tested and the results compared with wind tunnel results obtained by Campagnolo; using this method we compared different design and introduced a performance index to characterize the wheel performances. We performed brief analysis using and unsteady state model and a rigid body motion to compare the method with the steady model. Good agreement with experimental wind tunnel studies suggests that the approach we outline holds considerable promise. Owing to the flexibility of this methodology, it is now possible to use CFD to provide more definitive answers on some of the open questions within the competitive cycling and triathlon communities. Additional word regard the testing of an open-source code, because commercial codes are indeed expensive, we tried a simple three-spoke model with the OpenFOAM code, and highlight the pro and the cons of an open-source code. Finally, there is a brief description of different force balance layouts