A5018554764- Rheology and Fluid Dynamics Studies
- Fluid Dynamics and Turbulent Flows
- Fluid Dynamics and Thin Films
- Fluid Dynamics and Heat Transfer
- Fluid Dynamics and Vibration Analysis
- Blood properties and coagulation
- Enzyme Production and Characterization
- Lattice Boltzmann Simulation Studies
- Microbial Metabolites in Food Biotechnology
- DNA and Nucleic Acid Chemistry
- CRISPR and Genetic Engineering
- Enzyme Catalysis and Immobilization
- Enzyme Structure and Function
- RNA Interference and Gene Delivery
- Material Dynamics and Properties
- RNA and protein synthesis mechanisms
- Pharmacogenetics and Drug Metabolism
- Advanced biosensing and bioanalysis techniques
- Phase Equilibria and Thermodynamics
- Protein purification and stability
- Vitamin D Research Studies
- Solidification and crystal growth phenomena
- Biochemical and Molecular Research
- RNA Research and Splicing
- Polymer crystallization and properties
Indian Institute of Technology Kanpur
2015-2024
Princeton University
2022
Indian Institute of Technology Indore
2006-2015
Savitribai Phule Pune University
1974-2009
National Chemical Laboratory
1987-2004
Indian Institute of Science Bangalore
1992-2002
University of Minnesota, Duluth
2002
Queen's University
1997-2001
University of Minnesota
2001
University of Wisconsin–Madison
1998
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...
Vitamin A is required for reproduction and normal embryonic development. We have determined that all- trans- retinoic acid (atRA) can support development of the mammalian embryo to parturition in vitamin A-deficient (VAD) rats. At day (E) 0.5, VAD dams were fed purified diets containing either 12 μg atRA per g diet (230 rat day) or 250 (4.5 mg supplemented with a source retinol (100 units retinyl palmitate day). An additional group was both combination palmitate. Embryonic survival E12.5...
Newtonian pipe flow is known to be linearly stable at all Reynolds numbers. We report, for the first time, a linear instability of pressure-driven viscoelastic fluid, obeying Oldroyd-B constitutive equation commonly used model dilute polymer solutions. The shown exist numbers significantly lower than those which transition turbulence typically observed flow. Our results qualitatively explain experimental observations in solutions rates where absent. discussed here should form stage hitherto...
Viscoelastic plane Poiseuille flow is shown to become linearly unstable in the absence of inertia, limit high elasticities, for ultradilute polymer solutions. While inertialess elastic instabilities have been predicted curvilinear shear flows, this first ever report a purely linear instability rectilinear flow. The novel continues up Reynolds number (Re) $O(1000)$, corresponding recently identified elasto-inertial turbulent state believed underlie maximum-drag-reduced regime. Thus, highly...
A modal stability analysis shows that pressure-driven pipe flow of an Oldroyd-B fluid is linearly unstable to axisymmetric perturbations, in stark contrast its Newtonian counterpart which stable at all Reynolds numbers. The dimensionless groups govern are the number, elasticity and ratio solvent solution viscosity. mode has a phase speed close base-state maximum over entire region relevant parameter space, implying belongs class viscoelastic center modes. Unlike transition dominated by...
Owing to nonlinear viscoelasticity, materials often show characteristic features that resemble those of thixotropy. This issue has been debated in the literature over past several decades, and experimental protocols have proposed distinguish thixotropy from viscoelasticity. In this work, we assess these by carrying out experiments using polymer solutions, thixotropic clay dispersions, modeling their behavior, respectively, FENE-P constitutive equation a viscoelastic aging model. We find...
A linear stability analysis of plane Poiseuille flow an upper-convected Maxwell (UCM) fluid, bounded between rigid plates separated by a distance $2L$ , has been carried out to investigate the interplay elasticity and inertia on stability. The is governed following dimensionless groups: Reynolds number $Re=\unicode[STIX]{x1D70C}U_{max}L/\unicode[STIX]{x1D702}$ $E\equiv W/Re=\unicode[STIX]{x1D706}\unicode[STIX]{x1D702}/(\unicode[STIX]{x1D70C}L^{2})$ where $W=\unicode[STIX]{x1D706}U_{max}/L$...
A purely elastic linear instability was recently reported for viscoelastic plane Poiseuille flow in the limit of ultra-dilute (solvent to solution viscosity ratio $\beta \gt 0.99$ ), highly (Weissenberg number $W \sim 1000$ ) polymer solutions, within framework Oldroyd-B model (Khalid et al. , Phys. Rev. Lett., vol. 127, 2021, pp. 134–502). This is first instance a strictly rectilinear shearing flow, with phase speed unstable ‘centre mode’ being close base-state maximum velocity at channel...
Experiments are performed to characterize the onset of laminar–turbulent transition in flow high-molecular-weight polymer solutions rigid microtubes diameters range $390~\unicode[STIX]{x03BC}\text{m}{-}470~\unicode[STIX]{x03BC}\text{m}$ using micro-PIV technique. By considering tubes such small diameters, present study probes higher values elasticity numbers ( $E\equiv \unicode[STIX]{x1D706}\unicode[STIX]{x1D708}/R^{2}$ ) compared existing studies, where $\unicode[STIX]{x1D706}$ is longest...
The onset of instability laminar flow in a tube with deformable walls is studied experimentally order to characterize how the affected by elastic (shear) modulus wall. To this end, rectangular blocks polydimethylsiloxane (PDMS) gels different shear moduli are fabricated cylindrical hole (of diameter 1.65 mm) which fluid (water) occurs due an imposed pressure difference. PDMS were range 21 - 608 kPa. When flows through tube, we find that radius changes slowly as function distance along flow,...
Rheological characterization of complex fluids subjected to cyclic shear-rate sweep often exhibits hysteresis. Since both viscoelastic and thixotropic materials show hysteresis loops, it is important understand distinguishing features (if any) in the same shown by either. Lately, there has been substantial work that attempts relate area enclosed loop with manner which shear rate varied cycle, order infer parameters a material. In this work, we use nonlinear Giesekus model study its response...
We show using Brownian dynamics simulations and theory how the shear relaxation modulus G(t) of dilute solutions relatively stiff semiflexible polymers differs qualitatively from that rigid rods. For chains shorter than their persistence length, exhibits three time regimes: At very early times, when longitudinal deformation is affine, approximately t(-3/4). Over a broad intermediate regime, during which chain length relaxes, t(-5/4). long mimics A model polymer as an effectively extensible...
We present a theory of the linear viscoelasticity dilute solutions freely draining, inextensible, semiflexible rods. The is developed expanding polymer contour about rigid rod reference state, in manner that respects inextensibility chain, and asymptotically exact rodlike limit where length L much less than its persistence Lp. In this limit, relaxation modulus G(t) exhibits three time regimes: At very early times, τ∥∝L8/Lp5 required for end-to-end chain to relax significantly after...
The stability of wall modes in fluid flow past a flexible surface is analyzed using asymptotic and numerical methods. Newtonian, while two different models are used to represent the wall. In first model, modeled as spring-backed, plate-membrane-type wall, second model considered be an incompressible viscoelastic solid finite thickness. limit high Reynolds number (Re), vorticity confined region thickness O(Re−1/3) near channel. An analysis carried out for Couette surface, results show that...
The linear stability of fully developed Poiseuille flow a Newtonian fluid in deformable neo-Hookean tube is analysed to illustrate the shortcomings extrapolating elastic model for wall outside its domain validity small strains solid. We show using asymptotic analyses and numerical solutions that description solid dramatically alters behaviour tube. flow-induced instability predicted exist creeping-flow limit based on approximation absent model. In contrast, new low-wavenumber (denoted by k )...
The stability of pressure-driven flow in a rectangular channel with deformable neo-Hookean viscoelastic solid walls is analysed for wide range Reynolds numbers (from Re ≪ 1 to ≫ 1) by considering both sinuous and varicose modes the perturbations. Pseudospectral numerical asymptotic methods are employed uncover various unstable modes, their boundaries determined terms elasticity parameter Γ = V η/( ER ) number RV ρ/η; here maximum velocity laminar flow, R half-width, η ρ respectively...