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Abstract: The dynamics of two-dimensional viscous vesicles in shear flow, withdifferent fluid viscosities $\eta { m in}$ and $\eta { m out}$ inside andoutside, respectively, is studied using mesoscale simulation techniques.Besides the well-known tank-treading and tumbling motions, an oscillatoryswinging motion is observed in the simulations for large shear rate. Theexistence of this swinging motion requires the excitation of higher-orderundulation modes beyond elliptical deformations in two dimensions.Keller-Skalak theory is extended to deformable two-dimensional vesicles, suchthat a dynamical phase diagram can be predicted for the reduced shear rate andthe viscosity contrast $\eta { m in}-\eta { m out}$. The simulation resultsare found to be in good agreement with the theoretical predictions, whenthermal fluctuations are incorporated in the theory. Moreover, the hydrodynamiclift force, acting on vesicles under shear close to a wall, is determined fromsimulations for various viscosity contrasts. For comparison, the lift force iscalculated numerically in the absence of thermal fluctuations using theboundary-integral method for equal inside and outside viscosities. Both methodsshow that the dependence of the lift force on the distance $y { m {cm}}$ ofthe vesicle center of mass from the wall is well described by an effectivepower law $y { m {cm}}^{-2}$ for intermediate distances $0.8 R { m p}\lesssim y { m {cm}} \lesssim 3 R { m p}$ with vesicle radius $R { m p}$.The boundary-integral calculation indicates that the lift force decaysasymptotically as $1-y { m {cm}}\lny { m {cm}}$ far from the wall.



Author: Sebastian Meßlinger, Benjamin Schmidt, Hiroshi Noguchi, Gerhard Gompper

Source: https://arxiv.org/







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