Aerodynamic drag is the main resistive force in cycling at high speeds and on flat terrain. CFD simulations and wind tunnel tests are the main tools to study cyclist aerodynamics and to develop new products. The low-turbulence test section of the Politecnico di Milano Wind Tunnel has been used for more than 10 years to perform measurements on cyclists. This work focuses on the analysis of three different setup configurations by means of the use of stationary CFD simulations. The first configuration, called “old table configura- tion”, is the one usually used to perform the tests; the second one, called “new table configuration”, consider a developed flat plate actually used for the study of scale model of trains; the third one, called “on ground configuration”, does not consider the flat plate placing the bike directly on the floor of the Wind Tunnel. Looking at the velocity field, with this work it was possible to highlight that the old table shape deforms the flow encountered by the bike. The best configuration is the new table one, since it does not modify the flow and has a smaller boundary layer compared to the third configuration. On the other hand, the drag area, calculated using the speed mean value in front of the bike, shows a good agreement between second and third configura- tion. This means that the bike on ground configuration is the one that could be adopted in the future as it compensates for the slight change in flow with improved ease of setup assembly and test management. In addition, a new approach to calculate the force on the bike removing the effect of the supports is proposed and a new methodology to take into account the variation of the blockage ratio as a function of the yaw angle is suggested.
La forza aerodinamica è la principale componente delle forze che agistono su un ciclista ad alte velocità su un terreno piatto. Simulazioni al CFD e test in galleria del vento sono i principali strumenti per studiare l’aerodinamica dei ciclisti. La camera di prova a bassa turbolenza della Galleria del Vento del Politecnico di Milano viene utilizzata da oltre 10 anni per effettuare misure sui ciclisti. Questo lavoro si concentra sull’analisi di tre diverse configurazioni di setup mediante l’uso di simulazioni CFD stazionarie. La prima configurazione, denominata "configurazione con tavolo vecchio", è quella solitamente utilizzata per eseguire i test; la seconda, denominata "configurazione con tavolo nuovo", considera una piastra piana sviluppata e utilizzata per lo studio di modelli in scala di treni; la terza, denominata "configurazione a terra", non considera la piastra piana posizionando la bicicletta direttamente sul pavimento della Galleria del Vento. Osservando il campo di velocità, con questo lavoro è stato possibile evidenziare che la configurazione con tavolo vecchio deforma il flusso che è incontrato dalla bicicletta. La configurazione migliore è quella del nuovo tavolo, poiché non modifica il flusso e presenta uno strato limite più piccolo rispetto alla terza configurazione. D’altra parte, drag area, calcolata utilizzando il valore medio della velocità davanti alla bicicletta, mostra un buon accordo tra la seconda e la terza configurazione. Ciò significa che la configurazione con bicicletta a terra è quella che potrebbe essere adottata in futuro, in quanto compensa la leggera variazione del flusso con una maggiore facilità di montaggio e di gestione dei test. Inoltre, viene proposto un nuovo approccio per calcolare la forza sulla bicicletta riducendo l’effetto dei supporti e viene suggerita una nuova metodologia per tenere conto della vari- azione del rapporto di bloccaggio in funzione dell’angolo di yaw.
Cycling aerodynamics: CFD analysis of different setups for measuring aerodynamic forces in the wind tunnel
Magistri, Paolo
2021/2022
Abstract
Aerodynamic drag is the main resistive force in cycling at high speeds and on flat terrain. CFD simulations and wind tunnel tests are the main tools to study cyclist aerodynamics and to develop new products. The low-turbulence test section of the Politecnico di Milano Wind Tunnel has been used for more than 10 years to perform measurements on cyclists. This work focuses on the analysis of three different setup configurations by means of the use of stationary CFD simulations. The first configuration, called “old table configura- tion”, is the one usually used to perform the tests; the second one, called “new table configuration”, consider a developed flat plate actually used for the study of scale model of trains; the third one, called “on ground configuration”, does not consider the flat plate placing the bike directly on the floor of the Wind Tunnel. Looking at the velocity field, with this work it was possible to highlight that the old table shape deforms the flow encountered by the bike. The best configuration is the new table one, since it does not modify the flow and has a smaller boundary layer compared to the third configuration. On the other hand, the drag area, calculated using the speed mean value in front of the bike, shows a good agreement between second and third configura- tion. This means that the bike on ground configuration is the one that could be adopted in the future as it compensates for the slight change in flow with improved ease of setup assembly and test management. In addition, a new approach to calculate the force on the bike removing the effect of the supports is proposed and a new methodology to take into account the variation of the blockage ratio as a function of the yaw angle is suggested.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/197377