Novel method to control the floating motion of a sphere in vertical wind

The feasibility of controlling a levitating sphere over a vertical fan array wind tunnel (FAWT) is investigated. Based on the Coanda effect, and using a velocity gradient to exert a horizontal force on the sphere in levitation, a control algorithm is developed, allowing translation in a horizontal plane and precise positioning of the levitating sphere across the vertical test section. By tuning the fans’ speeds as well as various parameters of the controller, the sphere was able to translate in aerodynamic levitation and in a stable manner.

In order to gain more stability, several stabilisation methods were investigated. The stability of the sphere was demonstrated to be proportional to the size of the sphere.

To further understand the phenomena at play, 3D flow measurements with a five-hole pressure probe allowed to visualise the air flow generated by the FAWT in two different configurations: a stationary levitation pattern, and a translation one. A motion tracking camera system was used to capture the motion of the sphere in the test volume.