arXiv subjects

Srikumar Warrier

Publications and source records attributed to Srikumar Warrier.

4 recordsLinked to original sources

arXiv2026

Trapping-loss transition via a saddle-node bifurcation in thermophoretic particle transport driven by a time-periodic vortex

The transport of inertial particles in unsteady flows is often governed by the competition between multiple migration mechanisms. We investigate the interplay between inertia-induced drift and thermophoretic migration in a time-periodic vortex containing a localized temperature field. Starting from the small-Stokes-number limit of the particle equations of motion, we derive a cycle-averaged radial migration model describing the slow evolution of suspended particles over timescales much longer than the forcing period. The competition between outward inertia-induced drift and inward thermophoretic migration gives rise to stable and unstable fixed points of the reduced radial dynamics, corresponding respectively to particle trapping states and separatrices bounding trapped trajectories. The existence and location of these states are shown to be governed by the dimensionless control parameter $\Pi$, which measures the relative strength of inertia-induced transport to the thermophoretic transport. As $\Pi$ is decreased below a critical value, the stable and unstable fixed points coalesce and disappear, resulting in the loss of particle trapping. Phase portraits, bifurcation diagrams, and local asymptotic analysis demonstrate that trapping is destroyed through a saddle-node bifurcation. The transition is further characterized by the vanishing of the dominant eigenvalue and the associated divergence of the relaxation time, indicative of critical slowing down. Additional calculations employing various other velocity and temperature profiles demonstrate that the trapping-loss mechanism is robust and not specific to a particular profile.

physics.flu-dyn↗

arXiv2025

Electrostatic enhancement of particle collision rates in atmospheric flows

Collisional growth of tiny particles is a fundamental process governing the growth of cloud droplets and the aggregation of ash particles in volcanic plumes, with direct implications for precipitation formation, cloud lifetime, and ash plume dynamics. The particles in these scenarios often carry electric charges. In this study, we investigate the collision dynamics of a pair of like charged dielectric spheres subjected to a uniaxial compressional flow, an important linear flow that captures key features of atmospheric straining motions. Finite particle size leads to electrostatic interactions that deviate from the point charge approximation, resulting in far field repulsion and near-field attraction, which in turn generate nontrivial particle trajectories and critical collision thresholds. For certain combinations of charge and size, the interplay between hydrodynamic and electrostatic forces creates strong radially inward particle relative velocities that substantially alter particle pair dynamics and modify the conditions required for contact. For uncharged particles, collision efficiency increases monotonically with particle size ratio. However, in the presence of electrostatic forces with high charge ratio values, the collision efficiency exhibits a nonmonotonic dependence, attaining a maximum at small size ratios and decreasing as the ratio increases, with a crossover beyond which larger particles become less favorable for collision. These results demonstrate that the same polarity charges on finite sized atmospheric particles do not necessarily inhibit collisions. Instead, they can enhance collisional growth for specific charge and size ratio combinations, revealing counterintuitive pathways relevant to cloud microphysical processes and volcanic ash aggregation in electrified atmospheric environments.

physics.flu-dyn↗

arXiv2024

Centre mode instability of a dilute particle-laden swirling jet in a swirl flow combustor

Linear stability of a locally parallel annular swirling jet laden with particles in a swirl flow combustor is considered. At low Stokes numbers, the eigenspectra of the particle-laden jet with uniform particle concentration shows three unstable modes namely centre, sinuous and varicose modes. As the Stokes number is increased to unity, the growth rates of the centre and shear layer modes reduces compared to that of the unladen swirling jet. The magnitude of the velocity eigenmodes peaks in the vortex core and decays radially outward. The variation in particle concentration occurs mostly in the vortex core and almost none in the shear layer. The strength of flow reversal at the jet centreline is given by the backflow parameter. An increase in the backflow parameter increases the growth rate of the centre mode. Non-uniformity in the base-state particle concentration is introduced using a Gaussian function varying in the radial direction and a reduction in the growth rate of the centre mode is seen compared to the uniform particle concentration profile. When the location of the peak of the base-state particle concentration profile is inside the vortex core, the centre modes are stable. Linearized vorticity budget analysis reveals that this is accompanied by a decrease in the net generation of perturbation vorticity in the axial direction and increased radial and azimuthal perturbation vorticity.

physics.flu-dyn↗

arXiv2022

Linear stability analysis of particle-laden planar jet in the dilute suspension limit

Particle laden flows are commonly seen in many industrial applications such as fluidized beds in process industry, air laden with abrasive particles in abrasive machining and particle laden plumes in chemical industries. In the present work, we perform local analysis of a particle laden planar jet in the dilute suspension regime. Unladen parallel planar jets have been extensive studied using normal modes and is shown to have two unstable modes namely sinuous and varicose modes. Sinuous modes are found to be more unstable compared to the varicose modes. In the present study, we investigate the effect of particles on the stability of planar jets. Addition of particles at low Stokes numbers (St) (fine particles) results in higher growth rates than that of the unladen jet. In the intermediate Stokes number regime, addition of particles have a stabilizing effect on both the sinuous and the varicose modes. Interestingly for St~10, the unstable varicose mode is completely damped. Increasing the Stokes number by increasing the particle size, both sinuous and varicose modes show increasing growth rates, while increasing density ratio has a stabilizing effect on the flow. For non uniform particle loading, additional modes apart from the sinuous and varicose modes are observed. These modes suggests occurrence of compositional instability with an increased particle accumulation in the shear layer that is an order of magnitude higher compared to that of the sinuous and varicose modes.

physics.flu-dyn↗