Numerical Study on the Characteristics of Air Flows through Helmet Bicycle Racing Using the Effect of Variation of Trailing Edge

Research on aerodynamics on racing bicycles always develops from time to time. The various geometry of a time-trial helmet produces different characteristics of fluid flow, this is due to the relative movements of air that are in the area throughout the body shape of the helmet. Basically the fluid flow that passes on a racing bicycle helmet will produce a drag force, where this must be minimized in order to hinder the pace of drivers to achieve maximum speed, so drivers should pay attention to how to design the geometry of helmet that should be used. Computational fluid dynamics (CFD) method is used to simulate the case studies in this research. In this study, four kinds of models trailing edge geometry was varied to determine where the most optimal in accepting the drag force. The validation was also conducted to determine the suitability of this study with prior research, where in this validation the results of this study are compared with the research owned (Sims and Jenkins, 2011). The results of this validation show that the resulting drag coefficient has a very small difference of 0.001. The four models are simulated with Reynold number values of 7.14 × 104, 1.00 × 105, and 1.16 × 105. The results of this study indicate that with differences in the geometry of the trailing edge affect the drag force that occurs. From the research result when Reynold 7.0 x 10 ^ 4, the drag force produced by model 3 is bigger than model 1 and 2 which is equal to 0.182 N. Whereas on Reynold which is bigger 1.16 x 10 ^ 5 model 3 receives drag smaller than model 1 and 2 which is equal to 0.283 N.  In the world of bicycle racing, the difference in the small drag force affects the speed of the bicycle and affects the resulting victory.