Drag Reduction Method for a Cylinder Using an Airfoil with a Free Rotating Shaft

Abstract

A novel drag reduction method for a cylinder using a pivoted airfoil is proposed in this study. The pivoted airfoil can rotate freely on a shaft so that the airfoil can head windward. First, we conducted a water tunnel test to validate the drag reduction method. Contrary to our expectation, the airfoil did not head windward completely. The airfoil started to move from an initial angle of 0º to a stable angle of about 14º. Next, we calculated the aerodynamic force of the airfoil by a computational fluid dynamics (CFD) method. The reason the airfoil did not head windward completely was revealed. This is because the sign of the moment coefficient around the rotating shaft changes with increasing angle of attack. The CFD simulation also revealed that the drag reduction method can decrease the drag by 34%.