A5033216852- Micro and Nano Robotics
- Rheology and Fluid Dynamics Studies
- Fluid Dynamics and Turbulent Flows
- Microfluidic and Bio-sensing Technologies
- Pickering emulsions and particle stabilization
- Fluid Dynamics and Thin Films
- Advanced Thermodynamics and Statistical Mechanics
- Blood properties and coagulation
- Particle Dynamics in Fluid Flows
- Material Dynamics and Properties
- Lattice Boltzmann Simulation Studies
- Molecular Communication and Nanonetworks
- Cavitation Phenomena in Pumps
- Advanced Materials and Mechanics
- Electrostatics and Colloid Interactions
- Nonlinear Dynamics and Pattern Formation
- Meteorological Phenomena and Simulations
- Genomics and Chromatin Dynamics
- Fluid Dynamics and Heat Transfer
- Granular flow and fluidized beds
- Modular Robots and Swarm Intelligence
- Computational Fluid Dynamics and Aerodynamics
- Experimental and Theoretical Physics Studies
- Geophysics and Gravity Measurements
- Orbital Angular Momentum in Optics
University of Edinburgh
2015-2024
University of Strathclyde
2024
Princeton University
2022
Skolkovo Institute of Science and Technology
2020
Scottish Universities Physics Alliance
2014-2019
Anstalt für Verbrennungskraftmaschinen List (Austria)
2010-2019
Central Aerohydrodynamic Institute
1999-2017
Institute of Physics and Technology
2009
Moscow Institute of Physics and Technology
2009
Leiden University
2004-2008
Viscoelastic fluids can exhibit striking flow instabilities under conditions where ordinary Newtonian are stable, owing to the nonlinear coupling of elastic and viscous stresses. This article provides perspectives on viscoelastic by integrating input from speakers at a recent international workshop: historical remarks, characterization flows, discussion experimental simulation tools, modern questions puzzles that motivate further studies this fascinating subject. The materials here will be...
It is presently believed that flows of viscoelastic polymer solutions in geometries such as a straight pipe or channel are linearly stable. Here we present experimental evidence can be nonlinearly unstable and exhibit subcritical bifurcation. Velocimetry measurements performed long, microchannel; flow disturbances introduced at the entrance system by placing variable number obstacles. Above critical rate size perturbation, sudden onset large velocity fluctuations indicates presence nonlinear...
We show, using differential dynamic microscopy, that the diffusivity of non-motile cells in a three-dimensional (3D) population motile E. coli is enhanced by an amount proportional to active cell flux. While mutants without flagella and with paralysed have quite different thermal diffusivities therefore hydrodynamic radii, their are same extent swimmers regime densities explored here. Integrating advective motion non-swimmers caused finite persistence-length trajectories predicts our...
In this Letter, we study the collective behaviour of a large number self-propelled microswimmers immersed in fluid. Using unprecedently large-scale lattice Boltzmann simulations, reproduce transition to bacterial turbulence. We show that, even well below transition, swimmers move correlated fashion that cannot be described by mean-field approach. develop novel kinetic theory captures these correlations and is non-perturbative swimmer density. To provide an experimentally accessible measure...
Solutions of long, flexible polymer molecules are complex fluids that simultaneously exhibit fluid-like and solid-like behavior. When subjected to an external flow, dilute solutions elastic turbulence—a unique, chaotic flow state absent in Newtonian fluids, like water. Unlike its counterpart, turbulence is caused by stretching aligning the can occur at vanishing inertia. While experimental realizations well-documented, there currently no understanding mechanism. Here, we present large-scale...
Swimming bacteria create long-range velocity fields that stir a large volume of fluid and move around passive particles dispersed in the fluid. Recent experiments simulations have shown long-time mean-squared displacement bath swimming exhibits diffusive behaviour with an effective diffusion coefficient significantly larger than its thermal counterpart. A comprehensive theoretical prediction this understanding enhancement mechanism remain challenge. Here, we adapt kinetic theory by Lin et...
Yield-stress materials, which require a sufficiently large forcing to flow, are currently ill-understood theoretically. To gain insight into their yielding transition, we study numerically the rheology of suspension deformable droplets in 2D. We show that displays yield-stress behavior, with remaining motionless below critical body-force. In this phase, jam form an amorphous structure, whereas they order flowing phase. Yielding is linked percolation transition contacts droplet-droplet...
The lid-driven cavity flow is a well-known benchmark problem for the validation of new numerical methods and techniques. In experimental studies with viscoelastic fluids in such flows, purely-elastic instabilities have been shown to appear even at very low Reynolds numbers. A finite-volume code, using log-conformation formulation, used this work probe effect viscoelasticity on appearance two-dimensional cavities wide range aspect ratios (0.125 ≤ Λ = height/length 4.0), different Deborah...
Abstract Self-propelled particles such as bacteria or algae swimming through a fluid are non-equilibrium systems where particle motility breaks microscopic detailed balance, often resulting in large-scale collective motion. Previous theoretical work has identified long-ranged hydrodynamic interactions the driver of motion unbounded suspensions rear-actuated (“pusher”) microswimmers. In contrast, most experimental studies microswimmer have been carried out restricted geometries both swimmers’...
When subjected to sufficiently strong velocity gradients, solutions of long, flexible polymers exhibit flow instabilities and chaotic motion, often referred as elastic turbulence. Its mechanism differs from the familiar, inertia-driven turbulence in Newtonian fluids is poorly understood. Here, we demonstrate that dynamics purely pressure-driven channel flows dilute polymer are organized by exact coherent structures take form two-dimensional traveling waves. Our results no linear instability...
The production rate of polymer fibers by extrusion is usually limited the appearance a series instabilities ("melt fracture") that lead to unwanted undulations surface. We present both qualitative and quantitative experimental evidence that-in addition previously known polymer-specific scenarios-there an intrinsic route towards melt fracture type phenomena: nonlinear ("subcritical") instability viscoelastic Poiseuille flow.
Recent studies of pressure-driven flows dilute polymer solutions in straight channels demonstrated the existence two-dimensional coherent structures that are disconnected from laminar state and appear through a subcritical bifurcation infinity. These travelling-wave were suggested to organise phase-space dynamics purely elastic elasto-inertial chaotic channel flows. Here, we consider wide range parameters, covering cases, demonstrate unstable when embedded sufficiently three-dimensional...
A collection of microswimmers immersed in an incompressible fluid is characterised by strong interactions due to the long-range nature hydrodynamic fields generated individual organisms. As a result, suspensions rear-actuated ‘pusher’ swimmers such as bacteria exhibit collective motion state often referred ‘bacterial turbulence’, large-scale chaotic flows. The onset pusher classically understood within framework mean-field kinetic theories for dipolar swimmers. In bulk two and three...
Using a retarded-motion expansion to describe the polymer stress, we derive low-dimensional model understand effects of elasticity on self-sustaining process that maintains coherent wavy streamwise vortical structures underlying wall-bounded turbulence. Our analysis shows at small Weissenberg numbers, Wi, enhances structures. At higher however, stresses suppress vortices (rolls) by calming down instability streaks regenerates rolls. We show this behavior can be attributed nonmonotonic...
Views Icon Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Twitter Facebook Reddit LinkedIn Tools Reprints and Permissions Cite Search Site Citation Marc-Antoine Fardin, Ovidiu Radulescu, Alexander Morozov, Olivier Cardoso, Julien Browaeys, Sandra Lerouge; Stress diffusion in shear banding wormlike micelles. J. Rheol. 1 November 2015; 59 (6): 1335–1362. https://doi.org/10.1122/1.4930858 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends...
Recent experiments show that shear-banded flows of semidilute wormlike micelles in Taylor-Couette geometry exhibit a flow instability the form Taylor-like vortices. Here we perform nonaxisymmetric linear stability analysis diffusive Johnson-Segalman model shear banding and nature this depends on applied rate. For experimentally relevant parameters, find at beginning stress plateau is driven by interface between bands, while most occupied bulk high-shear-rate band. Our work significantly...
We examine experimentally the deformation of flexible, microscale helical ribbons with nanoscale thickness subject to viscous flow in a microfluidic channel. Two aspects flexible microhelices are quantified: overall shape helix and frictional properties. The coefficients determined by our experiments consistent calculated values context resistive-force theory. helices is well described nonlinear finite extensibility. Under distributed loading, pitch distribution nonuniform, from this we...
We demonstrate an unexpected connection between isotropic turbulence and wall-bounded shear flows. perform direct numerical simulations of forced at large scales moderate Reynolds numbers observe sudden transitions from a chaotic dynamics to spatially simple flow, analogous the laminar state in wall bounded find that survival probabilities are exponential typical lifetimes increase superexponentially with number. Our results suggest both flows qualitatively share same phase-space dynamics.
Recently, detailed experiments on visco-elastic channel flow have provided convincing evidence for a nonlinear instability scenario which we had argued based calculations Couette flow. Motivated by these extend the previous to case of Poiseuille flow, using Oldroyd-B constitutive model. Our results confirm that subcritical is similar both types and transition occurs Weissenberg numbers somewhat larger than one. We provide convergence our expansion spatial structure mode drives instability....
Suspensions of rear- and front-actuated microswimmers immersed in a fluid, known respectively as "pushers" "pullers," display qualitatively different collective behaviors: beyond characteristic density, pusher suspensions exhibit hydrodynamic instability leading to motion active turbulence, phenomenon which is absent for pullers. In this Letter, we describe the dynamics binary pusher-puller mixture using kinetic theory large-scale particle-resolved simulations. We derive verify an criterion,...