Proposal of Surface-Rotating Ball for Wind-Tunnel Using Magnetic Suspension

A wind-tunnel system for a spinning ball has been proposed to measure aerodynamic forces acting on the body. In the proposed system, the ball is suspended and rotated by electromagnets. The forces are measured from the control signal for suspension. However, due to the non-uniformity of the magnetic fields, rotation around a horizontal axis suffered from drag torque caused by eddy currents induced in the surface of the ball. It led to high energy consumption in the electromagnets. In this work, a surface-rotation ball with an adjustable rotating axis is proposed and developed. The ball is suspended stably with various-attitude surface rotation.