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14:40   Aerodynamics in wintersports Chair: John Goff 14:40 20 mins FLOW VISUALIZATION OF DOWNHILL RACER IN ALPINE SKIING USING COMPUTATIONAL FLUID DYNAMICS Takeshi Asai, Hong Sungchan, Koichi Ijuin Abstract: In downhill alpine skiing, racers often exceed maximum speeds of 120 km/h, with air resistance substantially affecting their timing. To date, studies on air resistance in alpine skiing have used wind tunnels and actual skiers to examine the relationship between gliding posture and drag, as well as for the design of skiing equipment, including the suit. However, these studies do not reveal the flow velocity distribution and vortex structure around the skier. The present study used computational fluid dynamics (CFD) with the lattice Boltzmann method to show the relationship between flow velocity in the full tuck position (the downhill racer’s speed) and total drag. Furthermore, we visualised the flow around the downhill racer through CFD and examined its vortex structure. The results showed that the total drag force in the downhill racer model was 27.0 N at a flow velocity of 15 m/s; 46.2 N, at 20 m/s; 74.3 N, at 25 m/s; 107.6 N, at 30 m/s; 144.7 N, at 35 m/s; and 185.8 N, at 40 m/s. Moreover, the visualisation of the flow field indicated that the main locations where substantial drag was generated in the downhill racer model at a flow velocity of 40 m/s were the head, upper arms, lower legs, and thighs (including the buttocks). 15:00 20 mins ANALYSIS OF PERFORMANCE INDICES FOR SIMULATED SKELETON DESCENTS Chen Gong, Eric Rogers, Stephen Turnock, Christopher Phillips Abstract: In the winter Olympic sport of Skeleton, sliders sprint and load themselves onto the sled facing head forwards. The slider uses primarily their shoulders and torso to apply control to the direction of the sled as it progressively gains speed during its descent. These small control course keeping maneuvers alongside more severe use of toe tapping onto the ice will help determine the eventual trajectory of the sled. It is therefore of interest to consider for a possible trajectory what control actions will determine the fastest descent time and in particular what metrics should be examined. In this paper a three degree-of-freedom simulation has been developed to analyse the influence of different control strategies on the descent time of a bob-skeleton. A proportional-derivative (PD) controller is used to steer the simulation down a representation of the Igls ice-track. Parametric variations of the simulation's performance were analysed and compared to identify possible correlations for controllers assist the design of an optimal controller. Analysis of the results have identified positive correlations between descent time, transverse distance travelled and energy dissipation establishing that the fastest descent time is achieved by minimising the energy lost through the descent. 15:20 20 mins SOME RESULTS ON BOBSLEIGH AERODYNAMICS Harm Ubbens, Richard Dwight, Andrea Sciacchitano, Nando Timmer Abstract: For a long time sleighs have been used as a means of transportation. After the addition of a steering mechanism to the steel frame in the late 19th century, the sport of bobsleigh was born. This sport, also known as the Formula 1 of the Winter Games, reaches speeds over 135 km/hr over races where the winner leads the pack by only hundredths of a second. The design of modern bobsleighs is strictly regulated by the rules imposed by the International Bobsleigh & Skeleton Federation (IBSF). These rules are mainly imposed to guarantee the safety of the athletes but they also reduce the possibility of an unfair competition as larger teams have more resources to design and improve the bobsleigh. However, there is some freedom left in the design in order to gain marginal advantages over the competitors, as suggested by Dabnichki [1]. This paper will discuss the aerodynamic shape optimization of a two-men bobsleigh cowling to reduce the drag due to the misalignment of the front and rear cowling parts as a consequence of lateral rotation in a track bend. The bobsleigh cowling is optimized with the use of a parametrized Computational Fluid Dynamic analysis. A two-dimensional investigation is performed on the longitudinal symmetry plane where the misalignment of the front and rear cowling parts induces a gap. This analysis is performed to verify the flow behaviour through the gap and bobsleigh cavity. The flow through the gap reduces the pressure inside the cavity and therefore increases the suction force of the wake behind the bobsleigh, and hence increases the drag. After the flow behaviour is verified the three-dimensional shape of the bobsleigh will be altered through the optimization process and finally result in a cowling shape for reduced drag when front and rear cowling parts are laterally rotated with respect to each other.