A spinning ball

A spinning ball

Advisor : Pr. François Gallaire, EPFL

Key words : CFD, Magnus force, Lift

The levitation of a light table-tennis ball in a hair-drier stream is a famous table-top experiment. However, the exact origin of the phenomenon is still unclear. It is not clear for instance if the rotation contributes significantly to the lift via the Magnus force, or if the lift force is dominated by the asymetric jet division as it impacts the sphere, a phenomenon sometimes called Coanda effect.

experiment picture
Examples of levitating balls : (a) a large ball on a water jet (Garcia and Chomaz 2000); (b) a ping pong ball on an hair-dryer

The goal of this project, that should be conducted in tandem, is to devise a little experiment as well as a numerical project for solving the somewhat simpler two-dimensional problem of the levitation of a cylinder. The cylinder position will be fixed but free to rotate and the force acting on it will be measured. One looks for a jet source position and direction which brings the cylinder to dynamical equilibrium.