Aerodynamic Analysis and Drag Coefficient Evaluation of Time-Trial Bicycle Riders

Abstract

Evaluation of drag coefficient often requires wind tunnel experiments and can be prohibitively expensive if not impossible for large objects or systems. Computational Fluid Dynamics (CFD) aerodynamic analysis offers an alternative approach and can be used as a very effective design tool in many industries: automotive, aerospace, marine, etc. The main objective of this research is to investigate feasibility of using non-contact digitizers for developing finite element models of large objects for subsequent CFD analysis. The developed methodology is applied to investigation of time-trial bicycle rider efficiency. Companies competing in this class of racing spend millions trying to optimize bicycle and rider geometry in order to reduce aerodynamic drag. This project investigates an alternative way to optimize the aerodynamic efficiency of the rider, considering the rider contributes the majority of the drag force of the rider-bicycle system. If small riding position adjustments could be made to the rider's body during a race, drag may be significantly reduced. This idea, and the fact that the direction of wind impacting the rider can vary, influenced the concept of this project. It was hypothesized that adjusting the time-trial handlebars on the bicycle to stagger the fore-aft position of the rider's hands would influence the upper body to rotate slightly. This could then reduce the frontal area of the rider in the wind direction, therefore reducing the aerodynamic drag. To simulate this situation, the Konica Minolta VIVID 910 non-contact 3-D digitizer was used to scan two separate riders, each aboard a different bicycle, in several positions, as described above. The 3-D scans were then imported into the CFD software package Star-CCM+ and several simulations were run using each of the two rider-bicycle models. The initial simulations seemed to support the theory as the asymmetrical riding position experienced decreased drag at significant wind yaw angles while the normal riding position did not. A second study, using a different rider and bicycle, yielded less conclusive results. The two studies represent the groundwork for similar large system CFD analysis and provide useful recommendations for continued research into bicycle rider aerodynamics.