On the velocity jump discontinuity for single bubbles rising in a viscoelastic fluid

Dieter Bothe, Matthias Niethammer (TU Darmstadt, Germany), Günter Brenn (TU Graz, Austria).

It is well-known that bubbles rising in viscoelastic liquids may exhibit a jump discontinuity of the rise velocity as a critical bubble volume is exceeded. This phenomenon has been extensively investigated in the literature, both by means of experiments as well as numerical simulations. The occurrence of the velocity jump seems to be associated with a change of the bubble shape under formation of a pointed tip at the rear and to the appearance of a so-called negative wake with the liquid velocity behind the bubble pointing in the opposite direction to that in viscous Newtonian fluids.

We revisit this topic, building mainly on our recent numerical work. Besides detailed information on the employed methods and techniques, this talk reports findings from a local conformation tensor analysis, which is able to explain a true discontinuity in the terminal bubble rise velocity.

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