UBC Fluids Seminar

Weekly fluids seminar by researchers or guests at UBC.

++++ Dec 8, 2023 ++++

Bonus session!

Speaker: Arisa Yokokoji (OIST)

Title: Rheological effects on purely-elastic flow asymmetries in the cross-slot geometry

Abstract: Viscoelastic flows in the cross-slot geometry can undergo a transition from a steady symmetric to a steady asymmetric flow state, ostensibly due to purely-elastic effects arising beyond a critical flow rate, or Weissenberg number Wi. However, some reports suggest that shear thinning of the fluid’s viscosity may also play an important role in this transition. We employ a series of polymer solutions of varying rheological properties to investigate in detail how the interplay between fluid elasticity and shear thinning affects the onset and development of asymmetric flows in the cross-slot. Flow velocimetry is performed on each of the polymer solutions, and to assess the degree of fow asymmetry I in the cross-slot as a function of both Wi and a dimensionless parameter S quantifying the fow-rate-dependent extent of shear thinning. Typically, the flow field breaks symmetry as Wi is increased beyond a critical value, but the magnitude of I is found to also be dependent on S. For a few specific polymer solutions, the flow field recovers symmetry above a second, higher critical Wi as S becomes small. The experimental results are summarized in a flow state diagram in Wi-S space, showing the relationship between flow asymmetry and fluid rheology. Finally, to gain a deeper understanding of the effects of shear thinning, numerical simulations are performed using the linear simplified Phan-Thien-Tanner model. We demonstrate that the degree of both shear thinning and elasticity of the fuid, and their interplay, are important factors controlling elastic instabilities in the cross-slot geometry.

Bio: I obtained my MSc degree in polymer science from Osaka University, Japan in 2022. After that I began my work a PhD student at OIST under the supervision of Prof. Amy Shen on the Microfluidics Unit. My current interests are viscoelastic flow instabilities and elastic turbulence.

Speaker: Mauricio Andres Rios Maciel (OIST)

Title: Duplex electrochemical microfluidic device for co-detection of COVID-19 antibodies/Environmental viscosity tuning by enzyme activity on the droplet system

Abstract: In this talk I’ll go through two different works, on the first one we addressed the need for a tool to monitor humoral responses in the context of COVID-19 infections to discriminate between vaccine and natural-induced immunological markers. This was achieved by an electrochemical immunoassay based on screen-printed electrodes functionalized with gold nanoflowers (AuNf). Moreover, the immunosensor was integrated in a microfluidic platform in order to obtain a convection-driven transport of target analytes and reduce the detection time to less than 7 minutes while maintaining high sensitivity and selectivity. On the other work we tackle the question if enzyme activity can affect the microenvironment in terms of physical properties (i.e., viscosity), by recreating a droplet system obtained from liquid-liquid phase separation we obtained a biological relevant macromolecular crowding, we then investigated the effect of enzyme activity on the shear viscosity of the system, finding that the catalytic activity can lead to decrease in viscosity which can be related to an enhance diffusion of small molecules.

Bio: I am a PhD student in OIST (Okinawa Institute of Science and Technology) in Japan on the Microfluidics unit led by Prof. Amy Shen. I previously completed my Master in Biotechnology in Mexico City, where I focus on the effect of hydrogels for 3D in vitro cell cultures. Next, I joined Prof. Shen’s unit to work on microfluidic biosensors for an internship, and enrolled on the PhD program to focus on the behavior and mechanism of biological complex fluids.

++++ Dec 7, 2023 ++++

Speaker: M. F. Naccache (PUC-Rio)

Title: Microstructure and rheology in fluids of the oil industry

Abstract: Non-Newtonian fluids are widely used in a variety of research areas as well as numerous industrial applications, including the food, pharmaceutical, and petroleum industries. As rheologists, the internal structures of these complex fluids are of significant interest as it allows us to analyze and understand better the obtained results of rheological experiments. Looking specifically at the oil industry, there are several model fluids that are used to understand and improve some operations like re-start flow in pipelines, plug & abandonment, drilling and cementation. Rheology plays an important role in all these processes. Then, it is interesting to look and relate the fluid microstucture to rheology, to help understanding the effects of rheology in the processes. Cryo-Scanning Electron Microscopy (cryo-SEM) is a one reasonable means for observing and investigating the microstructure of complex fluids. Using this method, we show the microstructure of some fluids and nanofluids, and relate these microstructures to the rheology and to flow behavior. We present some promising implementation cases of this cryo-SEM approach for various non-Newtonian fluids.

Bio: Mônica F. Naccache is an Associate Professor in the Department of Mechanical Engineering at Pontifícia Universidade Católica do Rio de Janeiro, Brazil (PUC-Rio), where she served as head of the Department of Mechanical Engineering at PUC-Rio, from 2014 to 2021. She was visiting Professor at the University of British Columbia, in 2007-2008. Monica was founder of the Brazilian Society of Rheology (BSR), has served as president from 2017 to 2019, and is currently vice-president of the BSR. She organized four Brazilian Conferences on Rheology, the Workshop: Viscoplastic Fluids: From Theory to Applications in 2011 and was vice-chair of the 18th International Congress on Rheology, 2020. She currently serves as Associate Editor of the Physics of Fluids Journal.

Monica is a Mechanical Engineer and received her Master’s and DSc also in Mechanical Engineering at PUC-Rio. She has experience in the areas of fluid mechanics and rheology, focusing on numerical simulation of flows of non-Newtonian fluids, rheology of thixotropic and elasto-viscoplastic materials, and interfacial rheology. She has co-authored more than 65 publications in peer-reviewed journals and contributed as reviewer for Journal of Rheology, Journal of Non-Newtonian Fluids Mechanics, Rheologica Acta, Physics of Fluids, among others. Monica has a strong collaboration with industrial partners, including energy companies and cosmetic industries. Monica is vice-coordinator of the Rheology Group at PUC-Rio, a research group sponsored by Industry and Government agencies involving around 30 people including faculty, researchers, technicians, and students.

++++ Nov 30, 2023 ++++

Speaker: Marjan Zare (UBC)

Title: Unlocking the Secrets: Time-dependent yield stress materials and the liberation of methane bubbles

Abstract: Almost half of global methane emissions come from diverse aquatic environments, including natural lakes and industrial ponds. Methane production in these systems occurs in sediments that exhibit yield stress behaviour and are capped with water. Bubbles become trapped when buoyancy generates insufficient stress to yield the surrounding material. However, the small rising bubbles recorded in in-situ measurements do not conform to the stability criterion. This raises the question: how are these single bubbles released from these systems? In this talk, I will discuss our computational efforts and experiments aimed at understanding the effects of the time dependence of yield stress materials on the flow around rising single bubbles. I will show how nonuniform rheology influences the stability criterion of bubbles, as well as the shape and trajectory of ascending bubbles. I will demonstrate how the time dependency of these fluids facilitates bubble motion through the creation of self-generated networks. Finally, I will detail the role of these bubbles in transporting materials from sediments to the water layer.

Bio: Dr. Marjan Zare is the manager of the Complex Fluids laboratory and a Research Associate at the University of British Columbia. She uses experimental and computational tools to understand and model the rheology and flow of complex fluids, in particular yield stress fluids. Her research tackles problems of high relevance to GHG emission and Canada’s renewable and sustainable energy.

++++ Nov 23, 2023 ++++

Speaker: Marco E. Rosti (OIST)

Title: Polymeric turbulence at large Reynolds and Deborah numbers

Abstract: Turbulent flows containing modest amounts of long-chained polymers have remained an intriguing area of research since the discovery of turbulent drag reduction. Here, we perform direct numerical simulations of statistically stationary, homogeneous, and isotropic turbulent flows of dilute solutions of polymers at various Deborah numbers. We present evidence that there is a range of scales r over which the energy spectra and the structure functions show new scaling consistent with recent experimental results. In particular, we find that for small wavenumbers k, the kinetic energy spectrum shows Kolmogorov-like behavior which crosses over at a larger k to a novel, elastic scaling regime, E(k)~k^−ξ, with ξ ≈ 2.3. We uncover the mechanism of the elastic scaling by studying the contribution of the polymers to the flux of kinetic energy through scales, and show that this elastic behaviour is non-monotonic in the Deborah number. Finally, I’ll briefly show how the results change when the Reynolds number is reduced.

Bio: Marco Edoardo Rosti is an Assistant Professor at the Okinawa Institute of Science and Technology (OIST), Japan, since 2020. He received a Master in Aeronautical Engineering from Politecnico di Milano in 2013, and PhD in Aeronautical Engineering at City, University of London in 2016. Before joining OIST, he spent time as postdoctoral fellow at the KTH Royal Institute of Technology, Sweden, and at the University of Tokyo, Japan. Marco’s research interests are in the general area of multiphase turbulence and complex fluids. He was the recipient of the RYUMON Award for distinguished young researcher in fluid mechanics, by the Japanese Society of Fluid Mechanics in 2021, and he is associate editor of the European Journal of Mechanics/B and editor of Results in Engineering.

++++ Nov 16, 2023 ++++

APS DFD Special

Speakers: Zelai Xu, Jiahao Gong, Zhouyang Ge, Guodong Gai (all from UBC)

Titles: Hystereses in one-dimensional compression of a poroelastic hydrogel (Xu)

Spheroidal swimmers in viscosity gradients (Gong)

Activity-induced dynamics in dense binary suspensions of shakers (Ge)

Dynamics and Rheology of Immersed Elastic Capsules in A Simple Shear Flow (Gai)

Bio: Zelai Xu is currently in the third year of his Ph.D. program working with Professor James Feng. His focus lies in numerically simulating the interplay between flow fields and hydrogels. In the talk, Zelai is going to introduce his findings from his latest study, “Hystereses in one-dimensional compression of a poroelastic hydrogel”.

Jiahao Gong is a final-year Ph.D. candidate at the University of British Columbia. He earned his Bachelor’s and Master’s degrees in Mechanical Engineering from Shanghai Jiao Tong University and the University of California, San Diego, respectively. His research focuses on utilizing asymptotic methods and the reciprocal theorem to investigate the dynamics of active particles with various shapes in complex fluids. During APS DFD, he will give a presentation on the topic of spheroidal swimmers in the presence of viscosity gradients.

Zhouyang Ge is an international postdoc jointly hosted by UBC and KTH (Sweden). His expertise is in computational fluid dynamics and he is currently interested in problems at the intersection of fluid mechanics and active matter, e.g. the collective dynamics of microswimmers.

Guodong GAI is a PIMS-CNRS Postdoctoral Fellow at the University of British Columbia in Vancouver, Canada. His research is deeply rooted in applied mathematics and High-Performance Computing, using highly-resolved numerical methods for numerical investigation of multi-phase flows. The scope of his research encompass various domains such as the deformation of blood cells, the dynamics of solid angular particles in inertial flow, and droplet interactions with compressible flow, such as shock waves.

++++ Nov 9, 2023 ++++

Speaker: Aashish Goyal (UBC)

Title: An accurate and scalable Direction-Splitting solver for flows laden with non-spherical rigid bodies

Abstract: Flows laden with rigid bodies are ubiquitous in both industrial and natural environments. An accurate representation of particle-laden flows in a computational model requires O(10^9) spatial variables. I present an accurate and scalable solver for non-spherical rigid particle-laden flows implemented on PacIFiC, an in-house C/C++ parallel library to solve Partial Differential Equations. The solver uses a direction splitting algorithm to transform all three-dimensional Poisson problems into a sequence of three one-dimensional sub-problems, thus improving its scalability up to multiple thousands of cores. I employ this algorithm to solve mass and momentum conservation equations in flow laden with non-spherical fixed or moving rigid bodies. The presence of rigid bodies on the Cartesian grid is accounted for by modifying the diffusive, the advection, and the divergence terms to correctly capture the sharp changes in flow that occur in the vicinity of a fluid-solid interface. I demonstrate the accuracy, speed, and scalability of the solver and also show the expanded functionality of the solver to incorporate intricate geometries that are specified in STL files. Finally, I demonstrate two complex flow problems: (i) the influence of a neighbor on the forces experienced by a sphere placed near a wall and (ii) the force and torque distribution in a suspension of non-spherical particles.

Bio: Aashish is a final-year Ph.D. candidate at the University of British Columbia. He did his Bachelor’s and Master’s in Chemical Engineering from the Indian Institute of Technology, Kanpur, in India. His research interests involve the mathematical modeling of particle-laden flows on High-Performance Computing (HPC) platforms. As a part of his doctoral research, he has developed a fast and scalable code to solve non-linear Partial Differential equations for fluid flows containing non-spherical rigid bodies.

++++ Oct 26, 2023 ++++

Speaker: Pascale Garaud (UCSC)

Title: Multiscale asymptotic analysis of stratified turbulence at medium and low Prandtl number

Abstract: In this talk, I will present recent theoretical and numerical progress in modeling the dynamics of stratified turbulence in regimes appropriate to the Earth’s atmosphere and oceans, of the interiors of giant planets, and of stellar interiors. Multiscale asymptotic analysis reveals the existence of several different dynamical regimes, each with its specific set of scaling laws relating the turbulence properties to the stratification. Direct Numerical Simulations are then used to test and validate these model predictions.

Bio: Prof. Garaud is the Chair of the Department of Applied Mathematics at UC Santa Cruz, and a fellow of the American Physical Society. She specializes in the study of transport by turbulence in geophysical and astrophysical fluids.

++++ Oct 19, 2023 ++++

Speaker: Jean-Luc Thiffeault (UWisc)

Title: Stirring by microswimmers and their interaction with boundaries

Abstract: Microswimmers and active particles have become a key part of modern soft matter modeling. I will discuss two applications. The first involves how microswimmers affect their environment through their motion – that is, how much fluid stirring they provide. Recent experiments have measured the displacement of small microspheres and characterized their statistics with a high degree of precision, allowing us to test the validity of various theories. We will see how to explain the non-Gaussian statistics observed in experiments, and to predict key quantities such as the effective diffusivity. In the second part, we will examine the dispersion of the microswimmers themselves. How does their swimming, and their interactions with boundaries, dictate how they migrate down narrow channels, such as a pipette? The exact shape of the swimmer plays an important role, since it affects how swimmers align with boundaries.

Bio: Jean-Luc Thiffeault is a professor of Mathematics at University of Wisconsin - Madison. He received his PhD in Physics from the University of Texas - Austin. His research interests include transport and mixing in fluid dynamics, topology and dynamical systems, and microswimmers as active matter.

++++ Oct 12, 2023 ++++

Speaker: Vaseem Shaik (UBC)

Title: Active particles in inhomogeneous environments

Abstract: Active particles are living or non-living entities that convert stored energy to directed motion, and a suspension of these particles is termed active matter. Examples of active particles include nanorobots, microorganisms, birds, fish, and humans. These particles often navigate through inhomogeneous environments such as gradients in heat, light, nutrients, fluid viscosity, or density. They typically respond to these inhomogeneities by displaying directed motion up or down the gradients, known as taxis. Some well-known types of taxis are chemotaxis in chemical/nutrient gradients, phototaxis in light gradients, and gravitaxis in gravitational field.

Here I focus on the μm - mm sized particles swimming in fluid viscosity or density gradients. I discuss the recently understood taxis in viscosity gradients (viscotaxis). I also talk about how these particles behave as light when interacting with sharp viscosity gradients, and how this behavior can be described by a Snell’s like law. I then discuss a new taxis in density gradients (densitaxis), that possibly aids/hinders the diel vertical migration of planktonic organisms in oceans. I also talk about the mixing by these particles and different ways to quantify it. Lastly, I discuss the effect of noise and how the aforesaid inhomogeneities could be used to control active matter under confinements.

Bio: Vaseem obtained his PhD from Purdue University in 2020. In his research, Vaseem uses asymptotic techniques to understand the motion of particles or swimming organisms in complex flows. His current interests are fluid dynamics and non-equilibrium statistical mechanics of active matter.

++++ Oct 5, 2023 ++++

Speaker: Lisa Fauci (Tulane)

Title: Neuromechanical model of injured lampreys locomotion

Abstract: In some vertebrates such as lampreys, swimming function can be regained after spinal injuries, but the exact mechanism of this recovery is not well understood. One hypothesis is that amplified proprioceptive (body-sensing) feedback can allow an injured lamprey to regain functional swimming even if the descending signal is lost. Here we present a multiscale model of an undulatory swimmer whose neural signaling is driven by a phase oscillator model that is fully coupled to a viscous, incompressible fluid. We examine the effects of amplified feedback on swimming behavior, and show that in some cases, feedback amplification below a spinal lesion is sufficient to partially or entirely restore effective swimming behavior. This is joint work with Christina Hamlet (Mathematics, Bucknell University), Eric Tytell (Biology, Tufts University) and Jen Morgan (Marine Biological Lab, Woods Hole).

Bio: Lisa Fauci received her PhD from the Courant Institute of Mathematical Sciences at New York University, and directly after that joined the Department of Mathematics at Tulane University in New Orleans. Her research focuses on biological fluid dynamics, with an emphasis on using modeling and simulation to study the basic biophysics of organismal locomotion and reproductive mechanics. Lisa served as president of the Society for Industrial and Applied Mathematics (SIAM) in 2019-2020. In 2023, she was elected to the US National Academy of Sciences.

++++ Sep 28, 2023 ++++

Speaker: Xiaoyu Mao (UBC)

Title: A Unified Eulerian Variational Framework for Multiphase Fluid-structure Interaction

Abstract: Multiphase fluid-structure interaction is a bi-directional coupling between multiphase fluids with immersed/floating deformable structures. It is omnipresent in biological flows and marine/offshore engineering applications such as cardiovascular systems, offshore wind turbines, oil/gas platforms and ships. Of particular interest in this work is to develop a fully coupled continuum mechanics framework for multiphase and multicomponent fluid-structure interaction with contact dynamics and topology changes. The framework unifies the kinematic descriptions of both fluids and solids in a spatially fixed Eulerian frame of reference. Evolving fluid-fluid and fluid-solid interfaces are captured by the phase-field description. Specifically, we developed a novel interface and geometry-preserving phase-field method for consistent diffuse interface transition and accurate geometric representation. The proposed framework has been systematically assessed for an increasing complexity of problems such as multiple bubbles rising with surface tension effect, the flow passing an elastic solid and a cylinder-flexible plate system, contact of immersed deformable solids and a full-scale demonstration of ship-ice-water-air interaction. With our parallelized 3D FEM-based implementation, the framework enables high-performance computing and high-fidelity simulation of general multiphase FSI problems for both low and high Reynolds numbers.

Bio: Xiaoyu is a post-doctoral fellow in the Computational Multiphysics Lab under the supervision of Prof. Rajeev Jaiman at UBC. After defending his Ph.D. thesis in August, he is currently working on ANSYS funded project focusing on the numerical stability of fluid-structure interaction for biomechanics and marine engineering applications. He has developed the interface and geometry-preserving methods for a novel and general-purpose unified continuum mechanics framework, which can simulate multiphase fluid-structure interactions with contact dynamics and topology changes at low and high Reynolds numbers.

++++ Sep 21, 2023 ++++

Speaker: Zhouyang Ge (UBC)

Title: Rheology of periodically sheared suspensions undergoing reversible-irreversible transition

Abstract: Suspensions are fluids loaded with solid particles that interact hydrodynamically through the suspending fluid and non-hydrodynamically upon direct contact. Interestingly, when sheared periodically at low Reynolds number, the particle dynamics can undergo a reversible-irreversible transition (RIT) characterized by a critical strain amplitude: below this amplitude, all particles return to their original positions after each period; above it, they diffuse. In this talk, I will describe the corresponding rheology of this process. Specifically, I will show that there are at least four rheological signatures at the onset of RIT, and they are related to the emergent dynamics through a shear-induced microstructure that tends to be hyperuniform at steady state. Furthermore, I will discuss the possibility of a second transition threshold and the associated suspension rheology, even if the particles are only weakly adhesive. In general, these results suggest that non-hydrodynamic interactions dictate the particle dynamics, while hydrodynamic interactions influence the suspension rheology.

Bio: Zhouyang Ge obtained his PhD degree in fluid mechanics from KTH Royal Institute of Technology (Sweden) in 2020. Since then, he has been a postdoc at the Department of Mechanical Engineering, UBC (advised by Prof. Gwynn Elfring), as well as the Department of Engineering Mechanics, KTH (since 2022). In his research, Zhouyang develops computational fluid dynamics methods to simulate multiphase and complex flows. His current interests are suspension rheology and active matter.