1. Introduction
The shuttlecock used in the game of badminton is the very interesting subject of research from anaerodynamic point of view as the sport of badminton is one of the oldest and most popular sports in the world. The popularity of the game is so immense that over 160 countries have officially joined the Badminton World Federation. The shuttlecock has the smallest ballistic coefficient and exhibits the largest in-flight deceleration of any airborne sporting implement. In other words, the aerodynamic characteristics of badminton shuttlecocks are significantly different from balls used in other racquet sports. The centre piece of the game is no doubt a shuttlecock which is made of natural feathers with an open conical shape. Being a bluff body, the shuttlecock generates significant aerodynamic drag and complex flight trajectory. Initial velocities of shuttlecocks in the rang of 67 m/s are reduced in only about 0.6 sec to near the terminal velocity of roughly 7 m/s[1]. Unlike most racquet sports, a badminton shuttlecock is an extremely high drag projectile and possesses almost parabolic flight trajectory. The hand-manufactured feather shuttlecock was the only available badminton projectile until the development of injection moulding as a manufacturing process had advanced enough to facilitate the production of synthetic shuttlecocks. In the future, it is possible that shuttlecocks may be manufactured with the use of carbon fibre technology. However, top class players still prefer the feather shuttlecock and consequently these are used in all major badminton competitions. These players believe that the synthetic shuttlecock still does not behave like a feather shuttlecock. Several researchers have measured the aerodynamic drag acting on a series of feather and synthetic shuttlecocks under a wide range of wind speeds to compare the results of synthetic shuttlecocks with feather shuttlecocks[2,3] and computer simulations of shuttlecock trajectories have been reported[4]. Knowledge of aerodynamic properties of shuttlecocks can greatly assist both amateur and professional players to understand the flight trajectory as players require considerable skills to hit the shuttlecock for the full length of the court. However, the mechanism of inducing high drag in flight for shuttlecocks has not been clarified yet.
In the present study, measurements of aerodynamic forces and flow visualization experiments were conducted in order to investigate the relationship between fluid forces and vortex behavior around a shuttlecock at high Reynolds numbers (200 km/h). The effect of shuttlecock deformation on aerodynamic properties was also investigated because it is presumed that flight mechanics are affected by the deformation of the shuttlecock skirt. The shuttlecock rotates about the shuttlecock’s major axis in actual flight, and the experiments were performed on shuttlecocks with and without rotation (spin). Furthermore, the effect of the flow passing through the gap between slots (stiffeners) located at leg portion of the shuttlecock skirt on aerodynamic characteristics is also demonstrated. Therefore, the shuttle was set up in the wind tunnel to examine the fluid force that acted on the shuttlecock, and the flow field was made visible with the measurement of the fluid force.