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Numerical investigation of swimming micro-organisms in complex environments
KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
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 [en]
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: urn:nbn:se:kth:diva-96819ISBN: 978-91-7501-411-1 (print)OAI: oai:DiVA.org:kth-96819DiVA: diva2:532908
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
List of papers
1. Locomotion by tangential deformation in a polymeric fluid
Open this publication in new window or tab >>Locomotion by tangential deformation in a polymeric fluid
2011 (English)In: Physical Reivew E, ISSN 1539-3755, Vol. 83, no 1, 011901- p.Article in journal (Refereed) Published
Abstract [en]

In several biologically relevant situations, cell locomotion occurs in polymeric fluids with Weissenberg number larger than 1. Here we present results of three-dimensional numerical simulations for the steady locomotion of a self-propelled body in a model polymeric (Giesekus) fluid at low Reynolds number. Locomotion is driven by steady tangential deformation at the surface of the body (the so-called squirming motion). In the case of a spherical squirmer, we show that the swimming velocity is systematically less than that in a Newtonian fluid, with a minimum occurring for Weissenberg numbers of order 1. The rate of work done by the swimmer always goes up compared to that occurring in the Newtonian solvent alone but is always lower than the power necessary to swim in a Newtonian fluid with the same viscosity. The swimming efficiency, defined as the ratio between the rate of work necessary to pull the body at the swimming speed in the same fluid and the rate of work done by swimming, is found to always be increased in a polymeric fluid. Further analysis reveals that polymeric stresses break the Newtonian front-back symmetry in the flow profile around the body. In particular, a strong negative elastic wake is present behind the swimmer, which correlates with strong polymer stretching, and its intensity increases with Weissenberg number and viscosity contrasts. The velocity induced by the squirmer is found to decay in space faster than in a Newtonian flow, with a strong dependence on the polymer relaxation time and viscosity. Our computational results are also extended to prolate spheroidal swimmers and smaller polymer stretching are obtained for slender shapes compared to bluff swimmers. The swimmer with an aspect ratio of two is found to be the most hydrodynamically efficient.

National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-30511 (URN)10.1103/PhysRevE.83.011901 (DOI)000286754100001 ()2-s2.0-78751500433 (Scopus ID)
Funder
Swedish Research CouncilSwedish e‐Science Research Center
Note

QC 20110315

Available from: 2011-03-15 Created: 2011-02-28 Last updated: 2014-03-13Bibliographically approved
2. Self-propulsion in viscoelastic fluids: pushers vs. pullers
Open this publication in new window or tab >>Self-propulsion in viscoelastic fluids: pushers vs. pullers
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
Keyword
Mixed Finite-Element, Hydrodynamic Interaction, Model Microorganisms, Nutrient-Uptake, Flow, Suspension, Particles, Stress, Viscosity, Rheology
National Category
Mechanical Engineering Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-96939 (URN)10.1063/1.4718446 (DOI)000304826100002 ()2-s2.0-84861980665 (Scopus ID)
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
3. Low-Reynolds number swimming in a capillary tube
Open this publication in new window or tab >>Low-Reynolds number swimming in a capillary tube
2013 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 726, 285-311 p.Article in journal (Refereed) Published
Abstract [en]

We use the boundary element method to study the low-Reynolds-number locomotion of a spherical model microorganism in a circular tube. The swimmer propels itself by tangential or normal surface motion in a tube whose radius is of the order of the swimmer size. Hydrodynamic interactions with the tube walls significantly affect the average swimming speed and power consumption of the model microorganism. In the case of swimming parallel to the tube axis, the locomotion speed is always reduced (respectively, increased) for swimmers with tangential (respectively, normal) deformation. In all cases, the rate of work necessary for swimming is increased by confinement. Swimmers with no force dipoles in the far field generally follow helical trajectories, solely induced by hydrodynamic interactions with the tube walls, and in qualitative agreement with recent experimental observations for Paramecium. Swimmers of the puller type always display stable locomotion at a location which depends on the strength of their force dipoles: swimmers with weak dipoles (small alpha) swim in the centre of the tube while those with strong dipoles (large alpha) swim near the walls. In contrast, pusher swimmers and those employing normal deformation are unstable and end up crashing into the walls of the tube. Similar dynamics is observed for swimming into a curved tube. These results could be relevant for the future design of artificial microswimmers in confined geometries.

National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-96940 (URN)10.1017/jfm.2013.225 (DOI)000319736300012 ()2-s2.0-84880231544 (Scopus ID)
Note

QC 20140311. Updated from "Submitted" to "Published"

Available from: 2012-06-13 Created: 2012-06-13 Last updated: 2017-12-07Bibliographically approved
4. Micropropulsion and microrheology in complex fluids via symmetry breaking
Open this publication in new window or tab >>Micropropulsion and microrheology in complex fluids via symmetry breaking
2012 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 24, no 10, 103102- p.Article in journal (Refereed) Published
Abstract [en]

Many biological fluids have polymeric microstructures and display non-Newtonian rheology. We take advantage of such nonlinear fluid behavior and combine it with geometrical symmetry-breaking to design a novel small-scale propeller able to move only in complex fluids. Its propulsion characteristics are explored numerically in an Oldroyd-B fluid for finite Deborah numbers while the small Deborah number limit is investigated analytically using a second-order fluid model. We then derive expressions relating the propulsion speed to the rheological properties of the complex fluid, allowing thus to infer the normal stress coefficients in the fluid from the locomotion of the propeller. Our simple mechanism can therefore be used either as a non-Newtonian micro-propeller or as a micro-rheometer.

Keyword
Biological fluids, Complex fluids, Deborah numbers, Micro propulsion, Micro-rheometers, Microrheology, Non-newtonian, Non-Newtonian rheology, Nonlinear fluids, Normal stress, Oldroyd-B fluid, Polymeric microstructures, Propulsion characteristics, Rheological property, Second-order fluids, Symmetry-breaking
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-96941 (URN)10.1063/1.4758811 (DOI)000310595100021 ()2-s2.0-84868629219 (Scopus ID)
Funder
Swedish e‐Science Research Center
Note

QC 20121205. Updated from submitted to published.

Available from: 2012-06-13 Created: 2012-06-13 Last updated: 2017-12-07Bibliographically approved

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