4 research outputs found
Experimental evidence of flow destabilization in a 2D bidisperse foam
Liquid foam flows in a Hele-Shaw cell were investigated. The plug flow
obtained for a monodisperse foam is strongly perturbed in the presence of
bubbles whose size is larger than the average bubble size by an order of
magnitude at least. The large bubbles migrate faster than the mean flow above a
velocity threshold which depends on its size. We evidence experimentally this
new instability and, in case of a single large bubble, we compare the large
bubble velocity with the prediction deduced from scaling arguments. In case of
a bidisperse foam, an attractive interaction between large bubbles induces
segregation and the large bubbles organize themselves in columns oriented along
the flow. These results allow to identify the main ingredients governing 2D
polydisperse foam flows
Dissipative flows of 2D foams
We analyze the flow of a liquid foam between two plates separated by a gap of
the order of the bubble size (2D foam). We concentrate on the salient features
of the flow that are induced by the presence, in an otherwise monodisperse
foam, of a single large bubble whose size is one order of magnitude larger than
the average size. We describe a model suited for numerical simulations of flows
of 2D foams made up of a large number of bubbles. The numerical results are
successfully compared to analytical predictions based on scaling arguments and
on continuum medium approximations. When the foam is pushed inside the cell at
a controlled rate, two basically different regimes occur: a plug flow is
observed at low flux whereas, above a threshold, the large bubble migrates
faster than the mean flow. The detailed characterization of the relative
velocity of the large bubble is the essential aim of the present paper. The
relative velocity values, predicted both from numerical and from analytical
calculations that are discussed here in great detail, are found to be in fair
agreement with experimental results
Viscous instabilities in flowing foams: A Cellular Potts Model approach
The Cellular Potts Model (CPM) succesfully simulates drainage and shear in
foams. Here we use the CPM to investigate instabilities due to the flow of a
single large bubble in a dry, monodisperse two-dimensional flowing foam. As in
experiments in a Hele-Shaw cell, above a threshold velocity the large bubble
moves faster than the mean flow. Our simulations reproduce analytical and
experimental predictions for the velocity threshold and the relative velocity
of the large bubble, demonstrating the utility of the CPM in foam rheology
studies.Comment: 10 pages, 3 figures. Replaced with revised version accepted for
publication in JSTA