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Position open for 1 B.Tech/M.Tech project (IITB Research internship program)
Research is an attitude, not an activity
Research is an attitude, not an activity
Animation of a thin free-film rupturing due to surface viscosity. The usual singular pinch-off is effectively smoothened out due to surface viscous effects.
Animation of a thin free-film of a octane-toluene liquid mixture with a plateau border (intersection of foam cells). The drainage is driven by Laplace pressure gradient but is hindered by complex Marangoni effects.
Thin film hydrodynamics
Thin film hydrodynamics
Modeling rheology: surface viscosity and elasticity.
The hydrodynamic mechanism of rupturing thin free-films helps us understand long shelf lifes of foams and emulsions. We have explored the modelling of surface viscous effects by systematically inculcating it in the interfacial jump conditions. Using a phenomenological model, we discovered enhanced stability of these thin free-films, deriving a mathematical condition for arbitrary long rupture times. It would be interesting to see how other physical mechanisms like interfacial elasticity can compete with surface viscous and Marangoni effects and fundamentally change our current understanding of hydrodynamic mechanisms.
Modeling rheology: surface viscosity and elasticity.
The hydrodynamic mechanism of rupturing thin free-films helps us understand long shelf lifes of foams and emulsions. We have explored the modelling of surface viscous effects by systematically inculcating it in the interfacial jump conditions. Using a phenomenological model, we discovered enhanced stability of these thin free-films, deriving a mathematical condition for arbitrary long rupture times. It would be interesting to see how other physical mechanisms like interfacial elasticity can compete with surface viscous and Marangoni effects and fundamentally change our current understanding of hydrodynamic mechanisms.
Characterising stability of foams of liquid binary mixtures.
Thin films of liquid mixtures show a very interesting feature: they induce Marangoni effects originating from the concentration differences in the surface and the bulk. Recent research in this field hints towards a combined effect of solutal Marangoni and Gibbs elasticity. We have modelled such complicated effects and developed a self-consistent reduced order model which describes the physical mechanisms observed in experiments. Such a simplified model could prove to be useful in simulating more complicated geometries like the Scheludko cell or the Hele-Shaw configurations.
Characterising stability of foams of liquid binary mixtures.
Thin films of liquid mixtures show a very interesting feature: they induce Marangoni effects originating from the concentration differences in the surface and the bulk. Recent research in this field hints towards a combined effect of solutal Marangoni and Gibbs elasticity. We have modelled such complicated effects and developed a self-consistent reduced order model which describes the physical mechanisms observed in experiments. Such a simplified model could prove to be useful in simulating more complicated geometries like the Scheludko cell or the Hele-Shaw configurations.
Flow-field inside the mucus layer with an unintuitive transport direction. The metachronal wave due to cilia underneath moves to the left while the net mucus flow is towards the right.
Severe shortening of tear film breakup time and the associated transient flow-field.
CSF flow in perivascular spaces. Taken from Kelly & Thomas, Annu. Rev. Fluid Mech, 2023
Bio fluid mechanics
Bio fluid mechanics
Mucociliary clearance
The human pulmonary airways consist of a protective mucus layer sitting atop a bed of active cilia. These cilia move in a coordinated fashion to create a metachronal wave, which transports the mucus layer towards the bronchial tract. A key observation of diseased mucus (for e.g. in cystic fibrosis) is high viscoelasticity and reduced cilia motility. We have developed a hydrodynamic framework to include both these features to model mucociliary transport. Using asymptotic analysis, we derive an expression for net mucus flow rate which is validated by full DNS of a simplified problem geometry. Additional mechanisms like passive airflow due to breathing and mucus generation from the epithelium underneath could lead to a realistic model for the transport process.
Mucociliary clearance
The human pulmonary airways consist of a protective mucus layer sitting atop a bed of active cilia. These cilia move in a coordinated fashion to create a metachronal wave, which transports the mucus layer towards the bronchial tract. A key observation of diseased mucus (for e.g. in cystic fibrosis) is high viscoelasticity and reduced cilia motility. We have developed a hydrodynamic framework to include both these features to model mucociliary transport. Using asymptotic analysis, we derive an expression for net mucus flow rate which is validated by full DNS of a simplified problem geometry. Additional mechanisms like passive airflow due to breathing and mucus generation from the epithelium underneath could lead to a realistic model for the transport process.
Human tear films
Predicting the breakup time of human tear films is a hot topic in the diagnostic industry. Fairly common diseases like the dry eye syndrome may be caused due to several factors. One of the factors is a loss of membrane associated mucins (MAMs) at the corneal epithelium, in patches. Using commercial codes, we have tested mechanisms like inhomogeneous MAMs, modelled by variations in van-der-Waals forces and effective stratified viscosity modelled by negative slip at the epithelium. Our model successfully predicts the qualitative shortening of breakup times. However, other mechanisms based on recent experimental findings like bacterial growth dynamics, non-Newtonian rheology (viscoelasticity and shear-thinning) and inhomogeneous lipid layers are directions worth exploring.
Human tear films
Predicting the breakup time of human tear films is a hot topic in the diagnostic industry. Fairly common diseases like the dry eye syndrome may be caused due to several factors. One of the factors is a loss of membrane associated mucins (MAMs) at the corneal epithelium, in patches. Using commercial codes, we have tested mechanisms like inhomogeneous MAMs, modelled by variations in van-der-Waals forces and effective stratified viscosity modelled by negative slip at the epithelium. Our model successfully predicts the qualitative shortening of breakup times. However, other mechanisms based on recent experimental findings like bacterial growth dynamics, non-Newtonian rheology (viscoelasticity and shear-thinning) and inhomogeneous lipid layers are directions worth exploring.
New opening: (1) B.Tech/M.Tech project (IITB research internship program)
Cerebro-spinal fluid flow
Circulation of cerebrospinal fluid (CSF) through the brain helps transport solutes which includes nutrients, drugs, and metabolic wastes. This circulation has implications for neurodegenerative disorders, for tissue damage during stroke and cardiac arrest, and for flow-related disorders such as hydrocephalus. Recent experimental results reveal several features of this flow, but most flow dynamics are not fully understood, including its driving mechanisms. We propose computational and theoretical modelling of cerebrospinal fluid flow in two sub-systems corresponding to two distinct diseases: (i) flow in ventricular system to model hydrocephalus and (ii) flow across the perivascular space to model Alzheimer’s disease.
Cerebro-spinal fluid flow
Circulation of cerebrospinal fluid (CSF) through the brain helps transport solutes which includes nutrients, drugs, and metabolic wastes. This circulation has implications for neurodegenerative disorders, for tissue damage during stroke and cardiac arrest, and for flow-related disorders such as hydrocephalus. Recent experimental results reveal several features of this flow, but most flow dynamics are not fully understood, including its driving mechanisms. We propose computational and theoretical modelling of cerebrospinal fluid flow in two sub-systems corresponding to two distinct diseases: (i) flow in ventricular system to model hydrocephalus and (ii) flow across the perivascular space to model Alzheimer’s disease.
Relevant publications:
A Choudhury, M Filoche, NM Ribe, N Grenier, GF Dietze (2023). Journal of Fluid Mechanics 971, A33 PDF
A Choudhury, M Dey, HN Dixit, JJ Feng (2021). Physical Review E 103 (1), 013108 PDF
Kelley, D. H., & Thomas, J. H. (2023). Cerebrospinal fluid flow. Annual review of fluid mechanics, 55(1), 237-264.
Flow visualisation of the area near a moving contact line formed with air-water-glass system. The red curve depicts the air-water interface.
Simulations of a fixed cylinder in a granular shear-flow. The pink lines are the velocity profiles formed due to the Mu-I rheology and gravity direction.
Other systems with hydrodynamics
Other systems with hydrodynamics
Flow near moving contact lines
A contact line is an intersection of three phases, such as the rim of a droplet on a horizontal plane. The interfacial shape involving a static contact line can be characterised by a contact angle. However, a moving contact line is much more complicated and no "singularity-free" theory exists in literature. Generally speaking, the current models on moving contact lines uses an ad-hoc route of implementing an abrupt slip region right at the contact line. Our experimental work however provides new insights into modelling the complex phenomenon, shedding new light on smoothly varying slip regions . Nevertheless, many unanswered questions remain to be explored, like flow patterns observed near the contact line, which have long been known to contradict with existing theories.
Flow near moving contact lines
A contact line is an intersection of three phases, such as the rim of a droplet on a horizontal plane. The interfacial shape involving a static contact line can be characterised by a contact angle. However, a moving contact line is much more complicated and no "singularity-free" theory exists in literature. Generally speaking, the current models on moving contact lines uses an ad-hoc route of implementing an abrupt slip region right at the contact line. Our experimental work however provides new insights into modelling the complex phenomenon, shedding new light on smoothly varying slip regions . Nevertheless, many unanswered questions remain to be explored, like flow patterns observed near the contact line, which have long been known to contradict with existing theories.
Granular media flows in the continuum limit
Flows of granular media are largely modelled as discrete elements. Although it gives a much more accurate picture of the microscopic dynamics, it is restricted by the huge computaional power needed to simulate larger systems. The Mu-I rheology model is an efficient way of modelling granular media as a continuum, which has been proven to accurately predict simple systems like a granular collapse. Our group currently works on more complicated problems, specifically in using the Mu-I rheology to model granular media interacting with solid objects. This has important consequences in modelling real phenomena of interests like segregation, the observation that big particles separate from smaller ones in granular flows composed of grains of different sizes, and lift forces on mixing blades, which has been experimentally observed to be much higher than Newtonian/non-Newtonian fluids.
Granular media flows in the continuum limit
Flows of granular media are largely modelled as discrete elements. Although it gives a much more accurate picture of the microscopic dynamics, it is restricted by the huge computaional power needed to simulate larger systems. The Mu-I rheology model is an efficient way of modelling granular media as a continuum, which has been proven to accurately predict simple systems like a granular collapse. Our group currently works on more complicated problems, specifically in using the Mu-I rheology to model granular media interacting with solid objects. This has important consequences in modelling real phenomena of interests like segregation, the observation that big particles separate from smaller ones in granular flows composed of grains of different sizes, and lift forces on mixing blades, which has been experimentally observed to be much higher than Newtonian/non-Newtonian fluids.
Particles on liquid crystal interfaces
Particles on liquid crystal interfaces
Relevant publications:
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