Viscous rebound of a quasi-two-dimensional cylinder on a solid wall

The concept of apparent coefficient of restitution is extended, to describe the wall-bouncing of a cylinder falling in a viscous fluid. When the Stokes number (St) is increased, the coefficient of restitution increases from 0 to 1 over two decades of St, with a critical Stc=75±{}25 (compared to Stc≈10 for spheres). While rationalizing results from experiments and numerical simulations, we evidence the relevance of lumping the complex details of physical phenomena involved during contact into a simple concept based on the contact apparent roughness and elasticity. The increase of dissipation associated with the contact elasticity is well captured by a model based on solid contact time scale.