scholarly journals Squirming through shear-thinning fluids

2015 ◽  
Vol 784 ◽  
Author(s):  
Charu Datt ◽  
Lailai Zhu ◽  
Gwynn J. Elfring ◽  
On Shun Pak
Keyword(s):  
Asymptotic Analysis ◽  
Numerical Simulations ◽  
Rheological Properties ◽  
Reynolds Numbers ◽  
Shear Thinning ◽  
Fundamental Question ◽  
Low Reynolds Numbers ◽  
Shear Thinning Fluids ◽  
Micro Organisms ◽  
Shear Thinning Fluid

Many micro-organisms find themselves immersed in fluids displaying non-Newtonian rheological properties such as viscoelasticity and shear-thinning viscosity. The effects of viscoelasticity on swimming at low Reynolds numbers have already received considerable attention, but much less is known about swimming in shear-thinning fluids. A general understanding of the fundamental question of how shear-thinning rheology influences swimming still remains elusive. To probe this question further, we study a spherical squirmer in a shear-thinning fluid using a combination of asymptotic analysis and numerical simulations. Shear-thinning rheology is found to affect a squirming swimmer in non-trivial and surprising ways; we predict and show instances of both faster and slower swimming depending on the surface actuation of the squirmer. We also illustrate that while a drag and thrust decomposition can provide insights into swimming in Newtonian fluids, extending this intuition to problems in complex media can prove problematic.

scholarly journals Soft Matter Emerging Investigators Issue 2021 - "Propulsion of an elastic filament in a shear-thinning fluid at low Reynolds numbers"

Soft Matter ◽  
2021 ◽  
Author(s):  
Ke Qin ◽  
Zhiwei Peng ◽  
Ye Chen ◽  
Herve Nganguia ◽  
Lailai Zhu ◽  
...  
Keyword(s):  
Soft Matter ◽  
Reynolds Numbers ◽  
Shear Thinning ◽  
Low Reynolds Numbers ◽  
Elastic Filament ◽  
Low Reynolds ◽  
Micro Organisms ◽  
Surrounding Fluid ◽  
Shear Thinning Fluid ◽  
Flexible Appendages

Some micro-organisms and artificial micro-swimmers propel at low Reynolds numbers (Re) via the interaction of their flexible appendages with the surrounding fluid. While their locomotion have been extensively studied with...

scholarly journals Secondary instabilities in Taylor–Couette flow of shear-thinning fluids

2021 ◽  
Vol 933 ◽  
Author(s):  
S. Topayev ◽  
C. Nouar ◽  
J. Dusek
Keyword(s):  
Numerical Simulations ◽  
Couette Flow ◽  
Vortex Flow ◽  
Shear Thinning ◽  
Taylor Vortex ◽  
Shear Thinning Fluids ◽  
Taylor Vortex Flow ◽  
Viscous Shear ◽  
Taylor Couette ◽  
Shear Thinning Fluid

The stability of the Taylor vortex flow in Newtonian and shear-thinning fluids is investigated in the case of a wide gap Taylor–Couette system. The considered radius ratio is $\eta = R_1/R_2=0.4$ . The aspect ratio (length over the gap width) of experimental configuration is 32. Flow visualization and measurements of two-dimensional flow fields with particle image velocimetry are performed in a glycerol aqueous solution (Newtonian fluid) and in xanthan gum aqueous solutions (shear-thinning fluids). The experiments are accompanied by axisymmetric numerical simulations of Taylor–Couette flow in the same gap of a Newtonian and a purely viscous shear-thinning fluid described by the Carreau model. The experimentally observed critical Reynolds and wavenumbers at the onset of Taylor vortices are in very good agreement with that obtained from a linear theory assuming a purely viscous shear-thinning fluid and infinitely long cylinders. They are not affected by the viscoelasticity of the used fluids. For the Newtonian fluid, the Taylor vortex flow (TVF) regime is found to bifurcate into a wavy vortex flow with a high frequency and low amplitude of axial oscillations of the vortices at ${Re} = 5.28 \, {Re}_c$ . At ${Re} = 6.9 \, {Re}_c$ , the frequency of oscillations decreases and the amplitude increases abruptly. For the shear-thinning fluids the secondary instability conserves axisymmetry. The latter is characterized by an instability of the array of vortices leading to a continuous sequence of creation and merging of vortex pairs. Axisymmetric numerical simulations reproduce qualitatively very well the experimentally observed flow behaviour.

Towards a Multi-Flagella Architecture for E.coli Inspired Swimming Microrobot Propulsion

2008 ◽  
Author(s):  
Arash Taheri ◽  
Meysam Mohammadi-Amin
Keyword(s):  
Escherichia Coli ◽  
Reynolds Numbers ◽  
Helical Motion ◽  
Mesoscopic Scale ◽  
Low Reynolds Numbers ◽  
Left Handed ◽  
Low Reynolds ◽  
Localized Drug Delivery ◽  
Micro Organisms ◽  
Flow Inertia

One of the primary goals of medical micro and nano robots is to reach currently inaccessible areas of the human body and carry out a host of complex operations, such as minimally invasive surgery (MIS), highly localized drug delivery, and screening for diseases at their very early stages. One of the innovative approaches to design microrobot propulsion is based on the flagellar motion of bacteria [1]. Certain bacteria, such as Escherichia coli (E.coli) use multiple flagella often concentrated at one end of their bodies to induce locomotion. Each flagellum is formed in a left-handed helix and has a motor at the base that rotates the flagellum in a corkscrew motion. As pointed out by Purcell in his Lecture “Life at low Reynolds numbers” [2], microorganisms experience an environment quite different from our own. In particular, because of their small size (of the order of microns), inertia is, to them, essentially irrelevant. The fact that inertia is irrelevant for micro-organisms makes it difficult for them to move. The propulsive mechanisms based on flow inertia will not work on a mesoscopic scale. To overcome this problem, organisms living in low Reynolds number regimes have developed moving organelles which have a handedness to them. For instance, E. Coli’s flagella rotate with a helical motion, much like a corkscrew. This configuration produces patterns of motion that do not repeat the first half of the cycle in reverse for the second half, allowing the organisms to achieve movement in their environment.

Simulation and Analysis of Fluid Dynamic Behaviour of Foods during Filling Processes

2007 ◽  
Vol 2 (3) ◽  
Author(s):  
Eleonora Bottani ◽  
Roberto Rizzo ◽  
Giuseppe Vignali
Keyword(s):  
Dynamic Behaviour ◽  
Fluid Dynamic ◽  
Shear Thinning ◽  
High Viscosity ◽  
Inlet Section ◽  
Shear Thinning Fluids ◽  
Filling System ◽  
Time Required ◽  
Shear Thinning Fluid ◽  
Steady State Predictions

This research presents a model describing the behaviour of a non-Newtonian shear-thinning fluid during aseptic filling processes, in order to determine the influence of the behaviour of fluids on the performance of filling valves in aseptic beverage plants, mainly in terms of the time required to perform the filling process. The ultimate aim of the study is to explore the possibility of improving the accuracy of industrial filling processes, so as to be able to utilise them with high viscosity fluids.The numerical model, exploiting the Finite Elements Method (FEM), was designed using the commercial software Comsol Multiphysics, and validated by comparing the steady state predictions with outcomes of filling experiments performed in industrial laboratories. Hence, subsequent numerical simulations were performed to investigate the transition from laminar to turbulent flow for shear-thinning fluids under different pressure conditions, in 3D time-dependent configurations. Results of the simulations, performed on a low fat yoghurt, show that laminar flow subsists within the whole filling system when the Metzner-Reed Reynolds number at the inlet section of the valve is lower than approx 444.

Sign in / Sign up

Export Citation Format

Share Document