Aerodynamics of a skater leg

Abstract

The design of current skating suits is based on the assumption that the flow across the skater body parts is highly similar to cylinder flow. The latter features drag crisis behaviour, resulting in significant drag reduction at the critical Reynolds number. However, whether the aforementioned assumption is valid and whether a drag crisis along the different body parts occurs, so far remains unknown.

The goal of this study is to investigate Reynolds number effects along the leg of a skater mannequin. To do so, potential drag crisis behaviour is studied via robotic Particle Image Velocimetry and Infrared Thermography for speeds ranging between 5 m/s and 25 m/s. The boundary layer state and the critical velocity distribution along the leg, based on the wake width variation, are evaluated for the bare mannequin and the mannequin wearing a skating suit optimized for ∼ 15 m/s.

Results reveal drag crisis behaviour along the knee, lower and upper leg. Furthermore, the flow topology is not only governed by the leg geometry, but also by streamwise vortices. These streamwise vortices cause an increase of the wake width below the calf and a reduced velocity deficit behind the upper leg. Most significant differences in wake width between the bare and the dressed leg are observed at 17.5 m/s. The latter observation is also supported by the Infrared Thermography results.

It can be concluded that the flow across the leg partly differs from cylinder flow, mainly because of streamwise vortices that locally affect the drag crisis behaviour.