Aerodynamic drag measurement of a moving object in stationary air

Aerodynamic drag in sports can be assessed using a multitude of methods such as wind tunnel tests, computational fluid dynamics simulations or field tests. All these methods are able to simulate specific situations in sports. The goal of this study was to describe a measurement system that assesses the aerodynamic properties of textile covered cylinders in a special situation: contrary to wind tunnel measurements, fabric-covered samples were moved in stationary air over a distance of up to 20 m at speeds from 5 to 20 ms⁻¹. The measurement system showed a precision better than 2%. The course of the drag coefficient over speed was very similar to comparison measurements in a wind tunnel, but the drag coefficient was lower by up to 18% with respect to the wind tunnel and the speed at which the drag crisis occurred in the wind tunnel was higher by up to 10 ms⁻¹. Reasons could be a higher turbulence intensity in our measurement setup or, more likely, that the motion of the sample was too short to build up a steady air flow as in wind tunnels. The limited duration of the experiment, however, maybe brings it closer to the reality in situations in sports where the athlete's posture and/or direction of motion change frequently or for some aspects of sports ball aerodynamics.