AIRFOLIED DESIGN FOR ALPINE SKI BOOTS

Abstract

In sports where high speed is involved, races are often won by milliseconds. Any advantage can then be important in order to reach the success. The drag acting on the athletes is often the highest force that the athletes have to fight against and, even a small reduction of drag, can create an advantage in terms of performances. However, in sports like ski jumping, the aerodynamic involved gets to be more complex, involving drag and lift force. Wind tunnel measurements have been carried out in the last century in order to understand the physics behind phenomena linked to sport activities (for example ball aerodynamics) or in order to optimize postures and materials. With the performances enhancement as final goal the aerodynamics behind a number of sports have been previously studied. Posture optimization, low drag bycicles, skin suits or even the recent and famous Speedo swimming suits are only some of the achievements of the research carried out. In the present thesis, a wide approach to the topic with particular focus on textile aerodynamics has been used. The thesis has then be divided into two main areas: A research Area 1 named Textiles and their effect on the aerodynamics of athletes and referred RA1 where the influence of textiles and clothing equipement on the drag acting against the athletes have been studied and a Research Area 2 named Performances and Prototyping where more practical examples of how aerodynamics can directy affect athletes performances are given and exposed. In RA1 the topography of textiles have been studied and the surface structure properties has been linked to the aerodynamic properties with particular regards to drag reduction and turbulence tripping. In order to simplify the case the athlete’s body has been simplified as a serie of cylindrical shapes and tests have been carried out mostly on cylinders. Effect of yaw angle, different speed, different diameter, different roughness, different material and distance between body parts have been analyzed. At the same time, test on existing suits have been carried out and a mathematical model in order to estimate performances in speed skating has been made. In RA2 different side projects have been carried out and the results can be summarized as follow: Effects of body weight in ski jumping has been analyzed in order to figure out if the new rules imposed by the FIS (International Ski Federation) were effective in order to reduce the increasing problem of anorexia amongst ski jumpers. Wind tunnel measurements were carried out in order to find the aerodynamic forces acting on a ski jumper in his flight path. The experimental data were then implemented into a mathematical model which is able to simulate the in-run and the flight path. In cycling, the attention was focused on the posture assumed by the cyclists with the goal of reducing the drag while keeping a good biomechanical efficiency. The rules imposed by UCI (International Cycling Union) set the boundaries. However, a impressively good result has been obtained focusing the attention on each athlete and finding a subjective optimum posture for each of the athletes tested. A low drag ski boot have been designed with a airfoiled shape which permitted to obtain an impressive drag reduction on the total drag acting on a downhill skier. Speed skating suits have been tested in order to quantify the influence of different model suits on skating performances. The suit used by torwegian Olympic team of ski-cross has been designed using the knowledge acquired and presented in RA1. An impressive drag reduction has been obtained and it helped two norwegian athletes to win a silver and a bronze medal at theWinter Olympic Games in Vancouver 2010. As previously mentioned, the research areas are: Research Area 1 - Textiles and their effect on the aerodynamics of athletes Research Area 2 - Performances and prototyping The main contributions are: P1: Reducing the Athlete’s aerodynamics P2: Experimental analysis on parameters affecting drag force on athletes P3: Aerodynamic and comfort properties of single jersey textiles for high speed sports P4: Aerodynamic behavior of single sport jersey fabrics with different roughness and cover factors P5: Effect of different skin suits on speed skating performances P6: Aerodynamic optimization and energy saving of cycling postures for international elite level cyclists P7: Effects of body weight on Ski Jumping performances under the new FIS rules P8: Airfolied design for alpine skiers boots P9: Aerodynamic and Comfort Characteristics of A Double Layer Knitted Fabric Assembly for High Speed Winter Sports P10: A Low Drag Suit For Ski-Cross Competitions