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Self-propulsion in viscoelastic fluids: pushers vs. pullers
KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
Dept. of Mechanical and Aerospace Engineering, University of California, San Diego, USA.
KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0002-4346-4732
2012 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 24, no 5, 051902- p.Article in journal (Refereed) Published
Abstract [en]

We use numerical simulations to address locomotion at zero Reynolds number in viscoelastic (Giesekus) fluids. The swimmers are assumed to be spherical, to self-propel using tangential surface deformation, and the computations are implemented using a finite element method. The emphasis of the study is on the change of the swimming kinematics, energetics, and flow disturbance from Newtonian to viscoelastic, and on the distinction between pusher and puller swimmers. In all cases, the viscoelastic swimming speed is below the Newtonian one, with a minimum obtained for intermediate values of the Weissenberg number, We. An analysis of the flow field places the origin of this swimming degradation in non-Newtonian elongational stresses. The power required for swimming is also systematically below the Newtonian power, and always a decreasing function of We. A detail energetic balance of the swimming problem points at the polymeric part of the stress as the primary We-decreasing energetic contribution, while the contributions of the work done by the swimmer from the solvent remain essentially We-independent. In addition, we observe negative values of the polymeric power density in some flow regions, indicating positive elastic work by the polymers on the fluid. The hydrodynamic efficiency, defined as the ratio of the useful to total rate of work, is always above the Newtonian case, with a maximum relative value obtained at intermediate Weissenberg numbers. Finally, the presence of polymeric stresses leads to an increase of the rate of decay of the flow velocity in the fluid, and a decrease of the magnitude of the stresslet governing the magnitude of the effective bulk stress in the fluid.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. Vol. 24, no 5, 051902- p.
Keyword [en]
Mixed Finite-Element, Hydrodynamic Interaction, Model Microorganisms, Nutrient-Uptake, Flow, Suspension, Particles, Stress, Viscosity, Rheology
National Category
Mechanical Engineering Applied Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-96939DOI: 10.1063/1.4718446ISI: 000304826100002Scopus ID: 2-s2.0-84861980665OAI: oai:DiVA.org:kth-96939DiVA: diva2:533279
Funder
Swedish Research CouncilSwedish e‐Science Research Center
Note

Updated from "Submitted" to "Published". QC 20140127

Available from: 2012-06-13 Created: 2012-06-13 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Numerical investigation of swimming micro-organisms in complex environments
Open this publication in new window or tab >>Numerical investigation of swimming micro-organisms in complex environments
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. vii, 25 p.
Series
Trita-MEK, ISSN 0348-467X ; 2012:07
Keyword
Hydrodynamic interaction, swimming microorganisms, Low-Reynolds number swimming, stokes flow, squirmer, finite element method, boundary element method, viscoelastic fluid, polymeric flow, microrheology
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-96819 (URN)978-91-7501-411-1 (ISBN)
Presentation
2012-06-14, E3, KTH, Osquars Backe 14, Stockholm, 10:15 (English)
Opponent
Supervisors
Funder
Swedish e‐Science Research Center
Note

QC 20120613

Available from: 2012-06-13 Created: 2012-06-12 Last updated: 2013-04-09Bibliographically approved
2. Simulation of individual cells in flow
Open this publication in new window or tab >>Simulation of individual cells in flow
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, simulations are performed to study the motion ofindividual cells in flow, focusing on the hydrodynamics of actively swimming cells likethe self-propelling microorganisms, and of passively advected objects like the red bloodcells. In particular, we develop numerical tools to address the locomotion ofmicroswimmers in viscoelastic fluids and complex geometries, as well as the motion ofdeformable capsules in micro-fluidic flows.

For the active movement, the squirmer is used as our model microswimmer. The finiteelement method is employed to study the influence of the viscoelasticity of fluid on theperformance of locomotion. A boundary element method is implemented to study swimmingcells inside a tube. For the passive counterpart, the deformable capsule is chosen as the modelcell. An accelerated boundary integral method code is developed to solve thefluid-structure interaction, and a global spectral method is incorporated to handle theevolving cell surface and its corresponding membrane dynamics.

We study the locomotion of a neutral squirmer with anemphasis on the change of swimming kinematics, energetics, and flowdisturbance from Newtonian to viscoelastic fluid. We also examine the dynamics of differentswimming gaits resulting in different patterns of polymer deformation, as well as theirinfluence on the swimming performance. We correlate the change of swimming speed withthe extensional viscosity and that of power consumption with the phase delay of viscoelasticfluids. Moreover, we utilise the boundary element method to simulate the swimming cells in astraight and torus-like bent tube, where the tube radius is a few times the cell radius. Weinvestigate the effect of tube confinement to the swimming speed and power consumption. Weanalyse the motions of squirmers with different gaits, which significantly affect thestability of the motion. Helical trajectories are produced for a neutralsquirmer swimming, in qualitative agreement with experimental observations, which can beexplained by hydrodynamic interactions alone.

We perform simulations of a deformable capsule in micro-fluidic flows. We look atthe trajectory and deformation of a capsule through a channel/duct with a corner. Thevelocity of capsule displays an overshoot as passing around the corner, indicating apparentviscoelasticity induced by the interaction between the deformable membrane and viscousflow. A curved corner is found to deform the capsule less than the straight one. In addition, we propose a new cell sorting device based on the deformability of cells. Weintroduce carefully-designed geometric features into the flow to excite thehydrodynamic interactions between the cell and device. This interaction varies andclosely depends on the cell deformability, the resultant difference scatters the cellsonto different trajectories. Our high-fidelity computations show that the new strategy achievesa clear and robust separation of cells. We finally investigate the motion of capsule in awall-bounded oscillating shear flow, to understand the effect of physiological pulsation to thedeformation and lateral migration of cells. We observe the lateral migration velocity of a cellvaries non-monotonically with its deformability.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. xvi, 55 p.
Series
TRITA-MEK, ISSN 0348-467X
Keyword
Hydrodynamic interaction, swimming microorganisms, capsule, Stokes flow, finite element method, boundary integral method, general geometry Ewald method, spectral element method, viscoelastic fluid, cellular deformation, flow cytometry, cell sorting, microrheology
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-142557 (URN)978-91-7595-036-5 (ISBN)
Public defence
2014-03-28, Sal E1, Lindstedtsvägen 3, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20140313

Available from: 2014-03-13 Created: 2014-03-06 Last updated: 2014-03-14Bibliographically approved

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