129 The optimization study taking account of hysteresis in Discus

This paper describes the hysteresis in the aerodynamic properties of a discus near to its stalling angle. Wind tunnel tests were carried out with a full-size woman's discus. The experimental aerodynamic data D, L and M were obtained from wind tunnel tests as functions of the angle of attack. It was found that the drag, lift and pitching moment coefficients, C_D C_L and C_M, increase with increasing the angle of attack up to a stalling angle of 30°. Beyond the stalling angle, C_L and C_M decrease suddenly and abruptly with increasing angle of attack. On the other hand, recovery from the stall does not occur at the same stalling angle of 30° when the angle of attack decreases from the stall state; recovery actually occurs at 25°. The C_L -α(angle of attack) curve is almost the same when the angle of attack is less than 24°. Therefore, hysteresis occurs near the stalling angle.