arXiv subjects

Chandi Sasmal

Publications and source records attributed to Chandi Sasmal.

7 recordsLinked to original sources

arXiv2026

Contrary to Newtonian trends: Early flow transition and drag enhancement at low to intermediate Reynolds number flows of structured fluids

The flow of structured fluids, such as polymeric and micellar solutions, involves a strong two-way coupling between flow kinematics and internal microstructural dynamics, including polymer stretching, micellar scission, and reformation. These interactions yield complex nonlinear rheological responses, including viscoelasticity, shear-thinning, and thixotropy. In this study, we perform high-fidelity numerical simulations of micellar solution flow past a circular cylinder using the Modified Bautista-Manero (MBM) model, which couples a viscoelastic constitutive equation with a kinetic equation for fluidity to capture reversible micellar breakage and reformation. Model parameters are derived from quantitative fitting of experimental data for the EHAC-NaSal system. Our results reveal substantially richer flow dynamics than in Newtonian fluids under the same conditions. Transitions to unsteady flow occur at significantly lower Reynolds numbers, indicating greater instability driven by microstructural effects. At intermediate Reynolds numbers, micellar flows exhibit quasi-periodic behaviour, contrasting with classical periodic vortex shedding in Newtonian cases. Unlike the monotonic drag reduction in Newtonian fluids, micellar solutions show an anomalous drag increase. Wake characteristics reverse with regime: larger recirculation zones at low Reynolds numbers but more compact wakes in unsteady flows. Lift coefficients and Strouhal numbers are consistently increased. Vorticity fields display pronounced spatial localisation within thin near-wake shear layers. A dynamic mode decomposition analysis reveals coexisting unstable time-decaying and self-sustained modes in micellar flows, whereas only self-sustained modes appear in Newtonian cases.

physics.flu-dyn↗

arXiv2021

Flow dynamics of wormlike micellar solutions through a model porous media

The flow of viscoelastic wormlike micellar solutions (WLMs) in porous media is encountered in many practical applications like enhanced oil recovery or groundwater remediation. To understand the flow dynamics of these complex fluids in porous media, a model porous media consisting of a straight microchannel with micropore throats present in it, is very often used. In this study, we perform an extensive numerical investigation to understand the flow dynamics of wormlike micellar solutions based on the two-species Vasquez-Cook-McKinley (VCM) model for micelles through such model porous media. We find the existence of an elastic instability once the Weissenberg number exceeds a critical value; likewise, it was seen in many prior experimental and numerical studies dealing with polymer solutions. However, for the present case of a WLM solution, we observe that this elastic instability is greatly influenced by the breakage and reformation mechanisms of the wormlike micelles. In particular, we notice that the intensity of this instability (characterized by the fluctuating flow fields) increases as the Weissenberg number increases; however, beyond a critical value of it, this elastic instability and/or the flow field fluctuation is suppressed because of the breakage of long micelles. This is in contrast to the polymer solutions for which the flow field gradually transits to a more chaotic and turbulent-like state (or the so-called elastic turbulence state) as the Weissenberg number gradually increases. Additionally, we observe that the flow dynamics of these WLM solutions are strongly dependent on the type of micropore throat, the number of pore throats, and the spacing between two consecutive pore throats. An extensive discussion on the pressure drop and apparent viscosity is also presented in the present study.

physics.flu-dyn↗

arXiv2021

Effect of micelle breaking rate and wall slip on unsteady motion past a sphere translating in wormlike micellar solutions

In a recent numerical study, we have shown that the unsteady motion past a sphere translating steadily in a wormlike micellar solution is caused due to the breakage of long micelles downstream of the sphere once the Weissenberg number exceeds a critical value based on the two-species Vasquez-Cook-McKinley (VCM) constitutive model for wormlike micelles (C. Sasmal, Unsteady motion past a sphere translating steadily in wormlike micellar solutions: a numerical analysis, Journal of Fluid Mechanics, 912, A52, 2021). This study further shows that this unsteady motion is strongly influenced by the micelle breakage rate and wall slip present on the sphere surface. In particular, we find that the onset of this unsteady motion is delayed to higher values of the Weissenberg number as the micelle breakage rate decreases or, in other words, as the micelles become hard to break. Additionally, we observe that at some values of the micelle breakage rate, a transition in the flow field from steady to unsteady occurs as the Weissenberg number increases, and then again, a transition from unsteady to steady occurs as the Weissenberg number further increases. Therefore, there is a window of the Weissenberg number present in which one can see this unsteady motion past the translating sphere. On the other hand, we show that the presence of wall slip on the sphere surface suppresses this unsteady motion past the translating sphere, and a probable explanation for the same is provided in this study.

physics.flu-dyn↗

arXiv2021

Unsteady motion past a sphere translating steadily in wormlike micellar solutions: A numerical analysis

This study numerically investigates the ow characteristics past a solid and smooth sphere translating steadily along the axis of a cylindrical tube filled with wormlike micellar solutions in the creeping ow regime. The two-species VCM (Vasquez-Cook- McKinley) and single-species Giesekus constitutive models are used to characterize the rheological behaviour of micellar solutions. Once the Weissenberg number exceeds a critical value, an unsteady motion downstream of the sphere is observed in the case of two-species model. We provide the evidence that this unsteady motion downstream of the sphere is caused due to the sudden rupture of long and stretched micelles in this region, resulting from an increase in the extensional ow strength. The corresponding single-species Giesekus model for the wormlike micellar solution, with no breakage and reformation, predicts a steady ow field under otherwise identical conditions. Therefore, it further ascertains the evidence presented herein for the onset of this unsteady motion. Furthermore, we find that the onset of this unsteady motion downstream of the sphere is delayed as the sphere to tube diameter ratio decreases. A similar kind of unsteady motion has also been observed in earlier several experiments for the problem of a sphere sedimenting in a tube filled wormlike micellar solutions. We find a remarkable qualitative similarity in the ow characteristics between the present numerical results on the steadily translating sphere and prior experimental results on the falling sphere.

physics.flu-dyn↗

arXiv2016

Parameter-free prediction of DNA dynamics in planar extensional flow of semidilute solutions

The dynamics of individual DNA molecules in semidilute solutions undergoing planar extensional flow is simulated using a multi-particle Brownian dynamics algorithm, which incorporates hydrodynamic and excluded volume interactions in the context of a coarse-grained bead-spring chain model for DNA. The successive fine-graining protocol [1, 2], in which simulation data acquired for bead-spring chains with increasing values of the number of beads $N_b$, is extrapolated to the number of Kuhn steps $N_\text{K}$ in DNA (while keeping key physical parameters invariant), is used to obtain parameter-free predictions for a range of Weissenberg numbers and Hencky strain units. A systematic comparison of simulation predictions is carried out with the experimental observations of [3], who have recently used single molecule techniques to investigate the dynamics of dilute and semidilute solutions of $λ$-phage DNA in planar extensional flow. In particular, they examine the response of individual chains to step-strain deformation followed by cessation of flow, thereby capturing both chain stretch and relaxation in a single experiment. The successive fine-graining technique is shown to lead to quantitatively accurate predictions of the experimental observations in the stretching and relaxation phases. Additionally, the transient chain stretch following a step strain deformation is shown to be much smaller in semidilute solutions than in dilute solutions, in agreement with experimental observations.

cond-mat.soft↗

arXiv2016

Effect of stretching-induced changes in hydrodynamic screening on coil-stretch hysteresis of unentangled polymer solutions

Extensional rheometry and Brownian Dynamics simulations of flexible polymer solutions confirm predictions based on blob concepts that coil--stretch hysteresis in extensional flows increases with concentration, reaching a maximum at the critical overlap concentration $c^\ast$ before progressively vanishing in the semidilute regime. These observations demonstrate that chain stretching strengthens intermolecular hydrodynamic screening in dilute solutions, but weakens it in semidilute solutions. Flow can thus strongly modify the concentration dependence of viscoelastic properties of polymer solutions.

cond-mat.soft↗

arXiv2014

Brownian dynamics simulations of planar mixed flows of polymer solutions at finite concentrations

Periodic boundary conditions for planar mixed flows are implemented in the context of a multi-chain Brownian dynamics simulation algorithm. The effect of shear rate $\dotγ$, and extension rate $\dotε$, on the size of polymer chains, $\left $, and on the polymer contribution to viscosity, $η$, is examined for solutions of FENE dumbbells at finite concentrations, with excluded volume interactions between the beads taken into account. The influence of the mixedness parameter, $χ$, and flow strength, $\dotΓ$, on $\left $ and $η$, is also examined, where $χ\rightarrow 0$ corresponds to pure shear flow, and $χ\rightarrow 1$ corresponds to pure extensional flow. It is shown that there exists a critical value, $χ_\text{c}$, such that the flow is shear dominated for $χ< χ_\text{c}$, and extension dominated for $χ> χ_\text{c}$.

cond-mat.soft↗