Résumé
Flow fields behind a sphere settling in polymeric fluids are investigated using a Particle Image Velocimetry (PIV) technique. Complex features including both a negative wake and a surrounding cone are quantified. In particular, an oscillation zone, which takes place behind the negative wake, is identified for the first time. A physical understanding of various phenomena involved in the wake is gained. The damping phenomenon can be attributed to the viscoelastic properties and the surrounding cone stems from a propagation front of lateral viscoelastic wave emitted by the settling sphere. The oscillation frequency and open angle of the surrounding cone are theoretically related to a viscoelastic Mach number. Satisfactory agreement with experiments is observed.