Berlin 2008 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 27: Micro and Nano Fluidics II: Slipping + soft objects in flow

CPP 27.5: Talk

Thursday, February 28, 2008, 15:00–15:15, C 264

Motion of an elastic capsule in time dependent shear flow — •Steffen Kessler, Reimar Finken, and Udo Seifert — II. Institut für Theoretische Physik, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart

The motion of an elastic three-dimensional micro-capsule in a time dependent shear flow is studied numerically using a spectral method. The shape of the capsule and the hydrodynamic flow field are expanded into smooth basis functions. Analytic expressions for the derivative of the basis functions permit the evaluation of elastic and hydrodynamic stresses and bending forces at specified grid points in the membrane. Compared to methods employing a triangulation scheme, this method has the advantage that the resulting capsule shapes are automatically smooth, and few modes are needed to describe the deformation accurately. Better stability properties compared to simple boundary integral methods follow from this strategy, which has been tested successfully recently in linear shear flow. This code is used to study the response of capsules to a modulated shear flow. We examine both a purely oscillating shear rate and a modulated shear rate around a constant value. In the latter case, we focus on the question whether dynamical phase transitions can be induced by small modulations. Computations are performed for capsules both with spherical and ellipsoidal unstressed reference shape, different elastic parameters, and different viscosity contrasts.