A singularly altered streamline topology allows faster transport from deformed drops Pavan Kumar Singeetham, Sumesh P. Thampi, Ganesh Subramanian Journal of Fluid Mechanics, 2024 We analyse the effect of drop-deformation-induced change in streamline topology on the scalar transport rate (the Nusselt number $Nu$ ) in an ambient planar linear flow. The drop-phase resistance is assumed dominant, and the drop deformation is characterised by the capillary number ( $Ca$ ). For a spherical drop ( $Ca = 0$ ) in an ambient planar extension, closed streamlines lead to $Nu$ increasing with the Péclet number ( $Pe$ ), from $Nu_0$ , corresponding to purely diffusive transport, to $4.1Nu_0$ , corresponding to a large- $Pe$ diffusion-limited plateau. For non-zero $Ca$ , we show that the flow field consists of spiralling streamlines densely wound around nested tori foliating the deformed drop interior. Now $Nu$ increases beyond the aforementioned primary plateau, saturating in a secondary one that approaches $22.3Nu_0$ for $Ca \\rightarrow 0$ , $Pe\\,Ca \\rightarrow \\infty$ . The enhancement appears independent of the drop-to-medium viscosity ratio. We further show that this singular dependence, of the transport rate on drop deformation, is generic across planar linear flows; chaotically wandering streamlines in some of these cases may even lead to a tertiary enhancement regime.
Active compound particles in a quadratic flow: hydrodynamics and morphology Chaithanya K. V. S., Pavan Kumar Singeetham, Sumesh P. Thampi Soft Matter, 2023 The synergy between the fluid flow from an active core and the background flow enables the generation of diverse core–shell morphologies in microfluidic devices.
Dilute dispersion of compound particles: Deformation dynamics and rheology Pavan Kumar Singeetham, K. V. S. Chaithanya, Sumesh P. Thampi Journal of Fluid Mechanics, 2021 Compound particles are a class of composite systems in which solid particles encapsulated in a fluid droplet are suspended in another fluid. They are encountered in various natural and biological processes, for e.g. nucleated cells, hydrogels, microcapsules etc. Generation and transportation of such multiphase structures in microfluidic devices is associated with several challenges because of the poor understanding of their structural stability in a background flow and the rheological characteristics of their dispersions. Hence, in this work, we analyse the flow in and around a concentric compound particle and investigate the deformation dynamics of the confining drop and its stability against breakup in imposed linear flows. In the inertia-less limit (Reynolds number, $Re \\ll 1$ ) and assuming that the surface tension force dominates the viscous forces (low capillary number, $Ca$ , limit), we obtain analytical expressions for the velocity and pressure fields up to ${O}(Ca)$ for a compound particle subjected to a linear flow using a domain perturbation technique. Simultaneously, we determine the deformed shape of the confining drop correct up to ${O}(Ca^2)$ , facilitating the following. (i) Since ${O}(Ca^2)$ calculations account for the rotation of the anisotropically deformed interface, the reorientation dynamics of the deformed compound particles is determined. (ii) Calculations involving the ${O}(Ca^2)$ shape of the confining interface are found to be important for compound particles as ${O}(Ca)$ calculations make qualitatively different predictions in generalised extensional flows. (iii) An ${O}(Ca)$ constitutive equation for the volume-averaged stress for a dilute dispersion of compound particles was developed to study both shear and extensional rheology in a unified framework. Our analysis shows that the presence of an encapsulated particle always enhances all the measured rheological quantities such as the effective shear viscosity, extensional viscosity and normal stress differences. (iv) Moreover, linear viscoelastic behaviour of a dilute dispersion of compound particles is characterised in terms of complex modulus by subjecting the dilute dispersion to a small-amplitude oscillatory shear (SAOS) flow. (v) Various expressions pertaining to a suspension of particles, drops, and particles coated with a fluid film are also derived as limiting cases of compound particles.
Asymptotic Solutions of the Planar Squeeze Flow of a Herschel-Bulkley Fluid Pavan Kumar Singeetham, Vishwanath Kadaba Puttanna Journal of Physics Conference Series, 2018 In this study, we present the analysis of the squeeze flow of a Herschel-Bulkley fluid between parallel plates that are approaching each other with a constant squeeze motion. The classical lubrication analysis predicts the existence of a central unyielded zone bracketed between near-wall regions. This leads to the well-known squeeze flow paradox for viscoplastic fluids. Since the kinematic arguments show that there must be a finite velocity gradient even in the unyielded zone, thereby precluding the existence of such regions. This paradox may, however, be resolved within the framework of a matched asymptotic expansions approach where one postulates separate expansions within the yielded and apparently unyielded (plastic) zones. Based on the above technique, we circumvent the paradox, and develop complete asymptotic solutions for the squeeze flow of a Herschel-Bulkley fluid. We derive expressions for the velocity, pressure and squeeze force. The effects of the yield threshold on the pseudo-yield surface that separates the sheared and plastic zones, and squeeze force for different values of non-dimensional yield stress have been investigated.
Asymptotic solutions of the planar squeeze flow of a casson fluid Pavan Kumar Singeetham, Vishwanath Kadaba Puttanna Aip Conference Proceedings, 2018 In this study, we present the squeeze flow of viscoplastic fluid using Casson model between parallel plates that are approaching each other with constant squeeze motion. Based on the technique of matched asymptotic expansions, we develop the complete asymptotic solutions for the squeeze flow of viscoplastic Casson fluid model. We derive the expressions for velocity, stress and squeeze force. The effects of the yield threshold on the pseudo-yield surface that separates the sheared and plastic zones and squeeze force for different values of non-dimensional yield stress have been investigated.
Orientation dynamics of a spheroid in the simple shear flow of a weakly elastic fluid PK Singeetham, D Madival, P Garg, G Subramanian arXiv preprint arXiv:2505.23361 , 2025 2025 Citations: 1
A singularly altered streamline topology allows faster transport from deformed drops PK Singeetham, SP Thampi, G Subramanian Journal of Fluid Mechanics 997, A39 , 2024 2024 Citations: 2
Scalar transport from deformed drops: the singular role of streamline topology PK Singeetham, SP Thampi, G Subramanian arXiv preprint arXiv:2301.04843 , 2023 2023
Active compound particles in a quadratic flow: hydrodynamics and morphology KVS Chaithanya, PK Singeetham, SP Thampi Soft Matter 19 (41), 7963-7978 , 2023 2023 Citations: 2
Dilute dispersion of compound particles: deformation dynamics and rheology PK Singeetham, KVS Chaithanya, SP Thampi Journal of Fluid Mechanics 917, A2 , 2021 2021 Citations: 6
Inertia effects in the planar squeeze flow of a Bingham fluid: a matched asymptotics analysis PK Singeetham, VK Puttanna Advances in Fluid Dynamics: Selected Proceedings of ICAFD 2018, 839-849 , 2020 2020 Citations: 1
Dynamics of compound particles in a quadratic flow PK Singeetham, KVS Chaithanya, SP Thampi APS Division of Fluid Dynamics Meeting Abstracts, T05. 002 , 2020 2020
Viscoplastic fluids in 2D plane squeeze flow: a matched asymptotics analysis PK Singeetham, VK Puttanna Journal of Non-Newtonian Fluid Mechanics 263, 154-175 , 2019 2019 Citations: 23
Asymptotic Solutions of the Planar Squeeze Flow of a Herschel-Bulkley Fluid PK Singeetham, VK Puttanna Journal of Physics: Conference Series 1039 (1), 012037 , 2018 2018
Asymptotic solutions of the planar squeeze flow of a casson fluid PK Singeetham, VK Puttanna AIP Conference Proceedings 1953 (1), 100006 , 2018 2018
Squeezing of Bingham Fluid Between Two Plane Annuli S Pavan Kumar, KP Vishwanath Applications of Fluid Dynamics: Proceedings of ICAFD 2016, 385-396 , 2017 2017 Citations: 3
MOST CITED SCHOLAR PUBLICATIONS
Viscoplastic fluids in 2D plane squeeze flow: a matched asymptotics analysis PK Singeetham, VK Puttanna Journal of Non-Newtonian Fluid Mechanics 263, 154-175 , 2019 2019 Citations: 23
Dilute dispersion of compound particles: deformation dynamics and rheology PK Singeetham, KVS Chaithanya, SP Thampi Journal of Fluid Mechanics 917, A2 , 2021 2021 Citations: 6
Squeezing of Bingham Fluid Between Two Plane Annuli S Pavan Kumar, KP Vishwanath Applications of Fluid Dynamics: Proceedings of ICAFD 2016, 385-396 , 2017 2017 Citations: 3
A singularly altered streamline topology allows faster transport from deformed drops PK Singeetham, SP Thampi, G Subramanian Journal of Fluid Mechanics 997, A39 , 2024 2024 Citations: 2
Active compound particles in a quadratic flow: hydrodynamics and morphology KVS Chaithanya, PK Singeetham, SP Thampi Soft Matter 19 (41), 7963-7978 , 2023 2023 Citations: 2
Orientation dynamics of a spheroid in the simple shear flow of a weakly elastic fluid PK Singeetham, D Madival, P Garg, G Subramanian arXiv preprint arXiv:2505.23361 , 2025 2025 Citations: 1
Inertia effects in the planar squeeze flow of a Bingham fluid: a matched asymptotics analysis PK Singeetham, VK Puttanna Advances in Fluid Dynamics: Selected Proceedings of ICAFD 2018, 839-849 , 2020 2020 Citations: 1
Scalar transport from deformed drops: the singular role of streamline topology PK Singeetham, SP Thampi, G Subramanian arXiv preprint arXiv:2301.04843 , 2023 2023
Dynamics of compound particles in a quadratic flow PK Singeetham, KVS Chaithanya, SP Thampi APS Division of Fluid Dynamics Meeting Abstracts, T05. 002 , 2020 2020
Asymptotic Solutions of the Planar Squeeze Flow of a Herschel-Bulkley Fluid PK Singeetham, VK Puttanna Journal of Physics: Conference Series 1039 (1), 012037 , 2018 2018
Asymptotic solutions of the planar squeeze flow of a casson fluid PK Singeetham, VK Puttanna AIP Conference Proceedings 1953 (1), 100006 , 2018 2018
