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pogni, matteo (2017) Numerical study of bicycle racing wheels aerodynamic performances. [Ph.D. thesis]

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Abstract (english)

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.

Abstract (italian)

Migliorare l'aerodinamica delle biciclette da competizione è molto importante, infatti, a seconda delle condizioni, la resistenza aerodinamica è tra il 70% e il 90% della resistenza totale, oltretutto le forze laterali possono influire la stabilità del veicolo.
Questo lavoro si occupa principalmente dell'aerodinamica delle ruote per biciclette da competizione nel tentativo di sviluppare un modello matematico CFD per calcolare le prestazioni di diversi profili e configurazioni, le ruote infatti sono responsabili tra il 10% e il 15% del drag di una moderna bici da competizione.
Il lavoro è suddiviso in 5 capitoli, nella prima è dedicata alla letteratura scientifica sull'argomento, sull'aerodinamica della bici e delle ruote in specifico, la seconda è dedicata alla teoria delle simulazioni fluidodinamiche, poi si passa alla costruzione del metodo di lavoro, al primo modello sviluppato, i primi risultati e le conseguenti modifiche al modello e alla validazione con dati della galleria del vento, ottenendo un buon livello di validazione del metodo, in seguito ho sviluppato un modello su software opensource OpenFoam.
In conclusione una breve descrizione di possibili pedane di forza utilizzabili per i test in galleria del vento.

EPrint type:Ph.D. thesis
Tutor:Petrone, Nicola
Ph.D. course:Ciclo 29 > Corsi 29 > INGEGNERIA INDUSTRIALE
Data di deposito della tesi:03 June 2018
Anno di Pubblicazione:07 November 2017
Key Words:CFD, Racing bicycle, bicycle, aerodynamics, aerodinamica, biciclette, starccm+, openfoam
Settori scientifico-disciplinari MIUR:Area 09 - Ingegneria industriale e dell'informazione > ING-IND/06 Fluidodinamica
Struttura di riferimento:Dipartimenti > Dipartimento di Ingegneria Industriale
Codice ID:11240
Depositato il:14 Nov 2018 13:15
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