Berlin 2015 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 72: Microswimmers, Active Liquids I (joint session CPP, BP, DY)
CPP 72.5: Vortrag
Donnerstag, 19. März 2015, 17:15–17:30, PC 203
The many faces of drag in micro-swimming — •Jayant Pande1, Laura Merchant1,2, Jens Harting3, and Ana-S. Smith1,4 — 1Inst. for Theo. Phys., Friedrich-Alexander Univ., Erlangen, Germany — 2School of Phys. and Astronomy, Univ. of St. Andrews, Scotland — 3Dept. of Appl. Phys., Eindhoven Univ. of Technology, Eindhoven, the Netherlands — 4Ruđer Bošković Inst., Zagreb, Croatia
Although the theoretical study of micro-swimming is becoming increasingly important, the role of the drag force faced by swimmers–clearly one of the cornerstones of micro-locomotion–remains inadequately understood. We shed light in this talk on some of the fundamental ways in which this force affects micro-swimming, using a very simple yet versatile model of a bead-spring swimmer, based on the three-sphere design of Najafi and Golestanian. The drag force on these swimmers enters in various guises–through the influence of the mean bead shape, through any induced transitory shape changes during the swimming cycle if the beads are non-rigid, and through the fluid viscosity. We consider the effect of each contribution separately by letting the beads be of any shape as well as of rigid or flexible material, and by analyzing the various forces on them in fluid. We show that in general an increase in the drag force can have a net positive or a negative impact on the velocity, and it is the swimmer elasticity which decides this. Depending on the latter, we present precise expressions for the parameter ranges where the drag has opposing effects. We support the theory using lattice Boltzmann method-based simulations, and discuss the parts of the theoretical parameter space which are accessible to the simulations.