A review on aerodynamics and hydrodynamics in sports

Optimization of Ski Attitude for the In-Flight Aerodynamic Performance of Ski Jumping

Simple Summary

Flight distance determines the score of ski jumping and thus should be elongated in the competitions. Research has found that an analysis of aerodynamics is indispensable for ski jumping and the attitudes of athletes and skis are crucial factors to dictate the aerodynamic forces. As a follow-up to our previous computational fluid dynamics work, an optimization of the ski attitudes is conducted to maximize the lift-to-drag ratio under certain lift constraints. The optimal attitudes at these lift levels are of practical importance for athlete training and the angle of attack is proven to be pivotal for the optimal lift-to-drag ratio. The flow structures generated by the ski at the optimal attitudes are also discussed, together with a comparison with previous wind-tunnel measurements.

Abstract

The control and adjustment of in-flight attitudes are critical to enlarging the flight distance of ski jumping. As one of the most important gears, the skis provide sufficient lift and drag forces for the athletes, and thus their in-flight attitudes should be optimized to improve flight performance. Here, the lift-to-drag ratio of a ski jumping ski is optimized with/without a constraint of lift capacity. The ski attitude is defined by three Eulerian angles and the resulting aerodynamic characteristics are predicted by Kriging models, which are established based on computational fluid dynamics (CFD) data. The surrogated models are dynamically updated in the optimization process to ensure their accuracy. Our results find that the optimization of the lift-to-drag ratio should be constrained by a certain lift capacity to be more practical. The angle of attack of the ski dominates the optimal lift-to-drag ratio at different lift levels while the yaw and roll angles are almost independent of the constraint once the required lift coefficient surpasses 0.6. This thus suggests that the athletes should focus on the angle of attack when modifying the ski attitude in the flight, which may reduce the difficulties in their in-flight decision makings.

Towards more valid simulations of slopestyle and big air jumps: Aerodynamics during in-run and flight phase

OBJECTIVES

This study aimed to investigate air drag and lift during the in-run and flight phase of ski and snowboard slopestyle and big air, to allow more valid modeling of jumps and hence reduce injury risk.

DESIGN

We present an experimental, multiple single athlete study based on wind tunnel measurements of 4 skiers and 3 snowboarders.

METHODS

Measurements were carried out in a closed loop wind tunnel, measuring airflow speed and 3D forces acting on the athletes. Athletes performed trials in typical postures at 35, 60 and 85 km/h wearing slim-, regular- and wide fit apparel. Drag and lift area (c_DA; c_LA) were calculated and analyzed using linear and multiple regression to describe their dependencies on posture, apparel and speed.

RESULTS

c_DA values were higher than earlier assumed and ranged from 0.3 to 0.95 m² for skiers and from 0.35 to 0.55 m² for snowboarders, primarily dominated by posture, and followed by apparel. c_LA ranged from -0.1 to 0.45 m² for skiers and from 0.04 to 0.17 m² for snowboarders. To facilitate more valid jump modeling posture- and apparel-dependent formulations for air drag coefficients were provided and the consequences of sport specific differences on modeling were highlighted.

CONCLUSIONS

Applying the air drag coefficients and relationships determined in this study will help to improve validity of jump modeling in big air and slopestyle. The variability in aerodynamic forces in slopestyle and big air is caused by differences between sports, posture and apparel.