Flow and stability of a viscoelastic liquid curtain ANTOINE GAIL - LARD

Submitted for the DFD17 Meeting of The American Physical Society Flow and stability of a viscoelastic liquid curtain ANTOINE GAILLARD, LUC LEBON, MATTHIEU ROCHE, CYPRIEN GAY, SANDRA LEROUGE, LAURENT LIMAT, Laboratoire MSC, Matiere et Systemes Complexes, CNRS UMR 7057, Univ Paris Diderot, Paris, France — We experimentally investigate the flow of a sheet of viscoelastic liquid falling freely from a thin slit under gravity. We observe new phenomena that are not described by the Newtonian curtain theory derived by Brown and Taylor. For low-viscosity elastic fluids, the mean falling velocity does not reduce to a free fall, even far downstream from the slit: we observe a shift towards sub-gravity accelerations. This corresponds to a dramatic increase of the length of the transient regime where gravity is balanced by internal stress instead of inertia. The flow in the curtain is stable for dilute and semi-dilute aqueous solutions of polyethylene oxide (PEO), a flexible polymer, but it becomes time dependent and horizontally modulated for aqueous solutions of partially hydrolyzed polyacrylamide (HPAM), a semi-rigid polyelectrolyte. In the latter case, the curtain becomes varicose. This extrusion instability results from the existence of large vortices at the entrance of the slit, where the liquid undergoes a strong planar contraction, which creates over-fed and under-fed regions. Finally, we show that the varicose curtain is prone to hole opening in its thinner parts and may cease to exist. Antoine Gaillard Lab. MSC, Matiere Sys. Complex CNRS UMR 7057, Univ Paris Diderot Date submitted: 31 Jul 2017 Electronic form version 1.4