Incompressible-compressible transition in falling granular jets

Université Bordeaux 1, Laboratoire Ondes et Matière d'Aquitaine, CNRS UMR 5798 351 cours de la libération, 33405 Talence, France, EU

^(a) y.amarouchene@loma.u-bordeaux1.fr

Received: 20 February 2013
Accepted: 10 April 2013

Abstract

Through a systematic experimental investigation of the behavior of falling granular jets under the action of gravity for different particle sizes, funnel diameters and ambient air pressures, necessary conditions to obtain incompressible granular jets are identified. A transition from compressible (characterized by a significant density decrease along the propagation) to incompressible granular jets (characterized by a constant density) is observed. This transition depends solely on the aspect ratio between the diameter of the particles and the diameter of the funnel. Surprisingly, the incompressible liquid-like behavior observed here seems to find its origin in the balance between the heat flux and the dissipation in the funnel independently of the ambient fluid pressure. A simple granular hydrodynamic model provides a good description of the transition.