Numerical analysis of the flow around a speed skydiver

In speed skydiving, the skydiver aims at reaching the highest possible free-fall speed over a given phase of the jump. The athletes therefore jump in a head-down position. In the present article, the aerodynamics and flow field around a speed skydiver have been studied for the first time. First, we defined representative aerodynamic reference conditions and a model of the athlete. We then analyzed the flow field around the skydiver for this baseline case in detail for a Reynolds number based on model length of Re-l = 13.95 center dot 10(6) and identified the flow regions with the largest contributions to the overall drag. To decrease the drag and thus allow for an increase of the free-fall speed, we then implemented and tested multiple configuration modifications. Two main regions of large-scale separation strongly contribute to the overall drag: around the neck of the athlete and at the rear end of the backpack. We thus designed configuration modifications aimed at reducing one of these separation regions at the time: a spoiler-helmet configuration to shift the separation on the helmet downstream and thereby reduce the separation region around the skydiver's neck and shoulder region, a neck-brace configuration to reduce the volume of the re-circulation area by thickening the neck and thus filling in the neck cavity and smoothing the outer contour, and a boattail-backpack configuration to decrease the separation downstream of the backpack. Overall, the neck-brace configuration was most successful: it reduced the drag coefficient by 18.9% and achieved a more symmetric flow field with reduced side forces. Our results indicate that influencing the separation around the neck has a stronger effect on the overall drag and thus the skydiver's performance, and should thus be attempted first. The strong disturbance to the flow field caused by the separation at the athlete's neck affects the overall flow field. However, once this separation region is mitigated by suitable measures, the farther downstream separation at the backpack should also be reduced to be able to achieve further performance increases. (c) 2023 Elsevier Masson SAS. All rights reserved.