arXiv subjects

Subhasish Guchhait

Publications and source records attributed to Subhasish Guchhait.

3 recordsLinked to original sources

arXiv2026

Hydrodynamic capture and release of a microswimmer by a meniscus corner

Biological microswimmers alter their motility in complex corner geometries, facilitating their survival. However, the dynamical features of low-Reynolds-number swimming at corners remain undefined. Here, we use active droplet microswimmers near a confined meniscus in a microchannel as a model system to study how microswimmer-corner interactions determine swimming patterns. Combining experiments, theory and simulations, we show that pusher-type micrsowimmers are attracted towards a meniscus corner, followed by transient trapping and eventual escape. We demonstrate that hydrodynamic interactions with the wall-interface corner intimately dictate the attraction and trapping or escape of the microswimmer on the basis of its strength. We show that the swimming trajectory at the meniscus corner can be tuned depending on the type of the microswimmer, the corner geometry and the viscosity ratio for the liquid interface. Our study provides a simple way to manipulate microswimmers by exploiting their hydrodynamic interactions near corner geometries.

cond-mat.soft↗

arXiv2024

Flow fields around active droplets squeezing through tight confinements

Biological microswimmers, like euglena, deform their body shape to swim through tight confinements having length scales comparable to the microswimmer length scale. Recently, it was shown that self-propelling active droplets can also squeeze through tight microconfinements by elongating their shape. However, the evolution of the hydrodynamic signature, or the velocity field, generated by the active droplet, as it deforms its shape to swim through increasingly tight microconfinements, has remained scarcely studied. Using high-resolution fluorescence microscopy and $μ$-Particle Image Velocimetry (PIV) analysis, we show here that as the swimming active droplet deforms from a spherical shape to a `stadium'-like shape, and eventually to an elongated `capsule'-like shape in increasingly tighter microchannels, its hydrodynamic signature changes from a `pusher'-like velocity field to a `puller'-like velocity field, and finally to an asymmetric velocity field. We characterize such alterations in the active droplet dynamics using the distributions of the local velocity magnitude, axial and transverse components of the local flow velocity, vorticity, and the filled micelle concentration. Finally, we use finite-element based numerical simulations to explain the aforementioned evolution of the velocity field stemming from the underlying physico-chemical hydrodynamics in the presence of a thin lubrication film between the swimming active droplet and the tight microconfinement walls. The present work provides a comprehensive understanding of the chemo-hydrodynamic characteristics of active droplets navigating extreme confined spaces, which can be beneficial for many autonomous cargo-delivery applications.

cond-mat.soft↗

arXiv2022

Experimental And Numerical Studies Of Interaction Between Liquid Droplets And Hot Surfaces Under Different Conditions

In the present paper, experimental and numerical studies of interaction between different liquid droplets with different hot metal surfaces had been carried out and the obtained results were interpreted using graphs and pictures. Droplet impact, spreading, break-up, and leidenfrost phenomenon were observed with the help of video camera at 100 fps. The interaction studies were done at different surface temperatures and different droplet impinging velocities. Three metals and three liquids were selected for the present study. Copper, Aluminium and Steel were selected as metals with different roughness factors and at different temperatures, while in liquid entities, Methanol, Ethanol and Kerosene (Water was also used in some portion) were selected. The selections of the metals were based on thethermal diffusivity property as it influences the thermal interaction between droplet and the hot metal surface. The temperature range of metal surface was kept from 150° C to 425°C and the impinging velocity range of droplets were in the range of 2.4 - 4.9 m/s. For computational studies Ansys Fluent R3-2019 version was used. Numerical study for the interaction process was carried out using Volume of Fluid (VOF) method, solving Navier-Stokes and energy equations in a 2D-geometry transient simulation. Parameters like surface temperature, heat flux, and spreading ratio with respect to Weber number change were investigated and discussed in the present paper. The output of this study will be useful to understand the physical mechanisms better and to develop novel models for effective spray cooling system designs. The results show that for a lower value of Weber number, after impact the droplets spread less wide compare to high Weber number. The spreading ratio of droplets was almost constant or uniform for different surface temperature and it depends only on the surface roughness.

physics.flu-dyn↗