Aerodynamics of loose sports garments

Ski Cross rules require loose garments and skin suits are not allowed. This study investigated the aerodynamic behaviour of flapping garments of different looseness ratios (garment length to cylinder circumference) mounted on a horizontal cylinder. Three fabrics of different roughness were tested in a wind tunnel from 20 to 140 kph. Tight fitting textiles showed the standard flow transition and critical flow regime known from smooth and rough cylinders. Flapping textiles exhibited a higher drag coefficient (on average 1.5 times higher than the tight fitting fabrics in the subcritical regime), which decreased slightly with speed. The high drag coefficient can be attributed to the flutter amplitude which increases the wake diameter and prevents backward movement of the separation points. The looseness ratio (fineness ratio) affects the drag coefficient only marginally (drag decreases with the ratios).