Research

I work in broad areas of analytical and numerical fluid dynamics like hydrodynamic instabilities, micro-hydrodynamics, non-linear, stochastic modelling, and particle dynamics in context of geophysical flows. Some of the topics I am working on are listed below.

Dynamics of micro-plastics in surface gravity waves

Microplastics in the ocean are a very serious concern all over the world. These microplastics can be assumed as spheroidal particles. Anisotropic tracer particles attain preferential alignment in a linear wavy flow, depending on the particle's shape and oscillation's amplitude. Microplastics can be found in various sizes and shapes in the upper part of the ocean. We have analyzed the drift of a finite-size anisotropic particle and derived the higher-order correction, which depends on size using the perturbation expansion. We found that the drift of such particles can eighter increase or decrease depending on an initial orientation and size of a particle. Then we have studied the translation and orientation dynamics of finite-size anisotropic particles and derived the coupled non-linear evolution equation. Further we have shown that if linear flow approximation is good in analyzing microplastics' transport. In reality, microplastics can have a wide range of densities and are classified into positive and negative buoyant particles depending on the relative density of water. Negative buoyant particles tend to settle down in ocean. We studied the effect of orientation and size of such particles on settling. We showed that the particle's densities and size could alter the trajectory in a wave propagation direction. We obtain non-zero drift for the direction along with the gravity. The ratio of drift velocities in two directions can explain the amount of translation and settling of a finite-size particle. Then we begin with studying the effects of particle inertia in our coupled evolution equation and studied the drift and orientation of anisotropic particles at a wavy flow field. We demonstrate that considering such an effect could provide a complete picture of the transport and dynamics of microplastics in the upper part of the ocean can be described accurately.

Dynamical study on the orientation of an anisotropic particle in shear flows

We have studied the rotation dynamics of the settling particle in the induced uniform electric field. The motivation behind this study is to understand the dynamics of the orientation of ice crystals in a cloud with an external field. Particle orientation in an external field has also been used in microfluidic applications for the separation of anisotropic particles due to lateral migration. When an anisotropic particle experiences an electric field, it may generate rotation along with oscillation and may lead to chaotic behavior. However, as the field's strength increases, a particle is pinned to a specific angle. We further study the orientation dynamics of the particle with including particle and fluid inertia in the presence of the external field.

Then we investigate the effect of noise to the above study. The noise can be attributed to Brownian diffusion, particle-particle collision and anisotropic turbulence.

Rotational dynamics of an ice crystal in clouds

We have studied the orientation dynamics of an ice crystal subjected to a homogenous isotropic turbulence and electric field. It has been shown that most of the settling ice crystal attains the "horizontal" alignment in atmosphere. However, on-field observation revealed that this is not true for all ice crystals in clouds. We investigate the preferred alignment and rotational behavior of ice crystal on varying the intensity of turbulence and electric field. We show that, depending on parameter, these particles can exhibit field induced alignment which can change when direction of electric field changes. This electric field induced alignment can change the visibility and overall radiation budget of the cloud.

Stability of a multiple holdup solutions in an incline two-layered channel flow

Research in past have revealed that, unlike in a horizontal stratified channel flow, two-layered inclined channel flows can have multiple base state solutions. These base states differ by the location of the interface from the wall, called holdup. In a counter-current flow, two holdups solutions are identified; in a co-current flow, up to three base state solutions can be formed at the same parameters. We have analyzed the hydrodynamic stability of each holdup solution in both counter- and co-current flows with wall slip conditions. Neutral stability boundaries are presented for each base state, with comparisons made with the previous results obtained for the no-slip boundary condition. We found that the wall slip could have both stabilizing and destabilizing effects depending on the flow rates and the value of holdup—the location of an interface.

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