# Improving downhill skier aerodynamics

## Position optimizing of a downhill skier to minimize the drag forces

### In alpine skiing, only a few hundredths of a second can be the

difference between first and second place. The speed of an alpine skier is determined by the balance between the speed produced by the gravitational force and the speed lost due to the resistive forces. Aerodynamic drag accounts for 80-90% of the total resistive force of a downhill skier, hence, reducing the drag force is of high importance to increase speed. Small adjustments in position of the skier could reduce this drag force significantly, gaining valuable milliseconds in a race. By applying the power of CFD, position optimization of the skier can be performed.

A 3D model of the athlete is quickly and accurately obtained using modern, handheld 3D scanners. The skier is scanned in a low tuck position, baseline position, representing the athlete’s currently assumed optimal position. Furthermore, the scan is digitally modified to resemble the postures tested in a wind tunnel.

Knowledge of which body segments that contributes the most to a drag increase and which movement that could give the lowest increase when the optimal low tuck position is not an option is valuable. Computational fluid dynamics (CFD) simulations are performed to evaluate the drag force distribution across each part of the skier's body, providing a basis for new gliding postures. The posture in tucked positions is defined by the torso and thigh angle, thus, these are the variables of interest when investigating the relative changes from the baseline position.

From these results of the drag distribution and the flow profile, it can be concluded that the head, upper arms, lower legs, and thighs are the major sources of drag on a downhill skier. Thus, the drag can be reduced by straightening the airflow around the head, upper arms, lower legs, and thighs, due to decreased wake fields behind the downhill skier. The improved position gives 20 % less drag compared to the baseline position. This gives valuable input to athletes that can be applied in future training and races.