01. Experimental/Computational Fluid Dynamics

Aerodynamic characteristics of sports suits are an important factor in performance. Particularly in sports characterized by high-speed motion, where flow separation causes significant drag, the aerodynamic characteristics of the suits have substantial effects. The fluid forces acting on the body of competitors are influenced by the surface topology of the fabric, position and size of the seams, use of fasteners, and air permeability of the fabric. Ski jumpers attempt to fly as far as possible upon take-off in competitions, and the fabric used for ski jumping suits plays a crucial role in achieving favorable aerodynamic characteristics. It is generally assumed that ski jumping suits made from fabrics with low air permeability will have favorable aerodynamic characteristics. Therefore, the outstretched fabric was specified only to have a minimum air permeability (40 L/m2/s at a water pressure of 10 mmAq) under the rules and regulations. On the other hand, in our previous study, it was confirmed that stall delay occurs with increasing air permeability of the suit fabric, and an increase in flight distance can be expected. However, the effect of the air permeability of ski jumping suits on aerodynamic characteristics has not been completely clarified yet. In the present study, wind tunnel experiments were carried out on an elliptical cylinder clothed with ski jumping suit fabrics of different air permeability in order to investigate the relationship between aerodynamic forces and flow fields. Stall delay occurs and drag decreases with increasing air permeability. Stall characteristics were affected by the air permeability of the fabric because, for fabrics with higher air permeability, the flow permeates the surface of the elliptic cylinder through the fabric and flows out into the separation region through the fabric again．