Geometric Mixing, Peristalsis, and the Geometric Phase of the Stomach.
Arrieta JMediterranean Institute for Advanced Studies (CSIC-UIB), E-07190 Esporles, Spain; Área de Mecánica de Fluidos, Universidad Carlos III de Madrid, E-28911, Leganés, Spain.
Cartwright JHInstituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, Campus Fuentenueva, E-18071 Granada, Spain.
Gouillart ESurface du Verre et Interfaces, UMR 125 CNRS/Saint-Gobain, 93303 Aubervilliers, France.
Piro NÉcole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
Piro ODepartament de Física, Universitat de les Illes Balears, E-07071 Palma de Mallorca, Spain.
Tuval IMediterranean Institute for Advanced Studies (CSIC-UIB), E-07190 Esporles, Spain.
English
Mixing fluid in a container at low Reynolds number--in an inertialess environment--is not a trivial task. Reciprocating motions merely lead to cycles of mixing and unmixing, so continuous rotation, as used in many technological applications, would appear to be necessary. However, there is another solution: movement of the walls in a cyclical fashion to introduce a geometric phase. We show using journal-bearing flow as a model that such geometric mixing is a general tool for using deformable boundaries that return to the same position to mix fluid at low Reynolds number. We then simulate a biological example: we show that mixing in the stomach functions because of the "belly phase," peristaltic movement of the walls in a cyclical fashion introduces a geometric phase that avoids unmixing.