arXiv subjects

Ajay Harishankar Kumar

Publications and source records attributed to Ajay Harishankar Kumar.

3 recordsLinked to original sources

arXiv2026

Hydrodynamic Resistance on Oscillating Planar Interfacial Bodies

We study the unsteady dynamics of floating planar bodies undergoing lateral oscillations along an air-water interface. Scaling arguments indicate that at high Womersley number and small oscillation amplitude the flow beneath the body can be approximated by an oscillatory Stokes boundary layer, yielding a leading-order description of the hydrodynamic resistance. Using magnetic actuation, we drive the interfacial bodies harmonically and measure the amplitude response and phase lag in steady state over a range of frequencies, masses, sizes, and shapes. This frequency-response framework enables direct extraction of effective added mass and damping coefficients, which we find to be consistent with oscillatory boundary-layer theory in the limit of small interfacial deformation. The transient behavior during startup is also shown to be accurately predicted by a history integral that captures the development of the oscillatory boundary layer beneath the body. This work also establishes a simple experimental platform for quantifying unsteady hydrodynamic forces at fluid interfaces.

physics.flu-dyn↗

arXiv2022

Reconfigurable mechanical vibrations laboratory kit

Mechanical vibrations appear across a diverse range of applications, but nevertheless are unified by a core set of principles and phenomena. In this article, we describe a reconfigurable laboratory kit that is designed to be used as part of a first undergraduate course in mechanical vibrations. The kit was designed to be low-cost and allow for a series of laboratory experiments to be performed remotely. Using a common set of core hardware and software, five laboratory experiments are detailed and can be performed to supplement many of the major topics traditionally encountered in a first vibrations course. This accessible platform will readily enable further technical improvements and expansions, as well as the development of additional instructional modules.

physics.ed-ph↗

arXiv2021

Taylor dispersion of elongated rods

Particles transported in fluid flows, such as cells, polymers, or nanorods, are rarely spherical. In this study, we numerically and theoretically investigate the dispersion of an initially localized patch of passive elongated Brownian particles constrained to one degree of rotational freedom in a two-dimensional Poiseuille flow, demonstrating that elongated particles exhibit an enhanced longitudinal dispersion. In a shear flow, the rods translate due to advection and diffusion and rotate due to rotational diffusion and their classical Jeffery's orbit. The magnitude of the enhanced dispersion depends on the particle's aspect ratio and the relative importance of its shear-induced rotational advection and rotational diffusivity. When rotational diffusion dominates, we recover the classical Taylor dispersion result for the longitudinal spreading rate using an orientationally averaged translational diffusivity for the rods. However, in the high-shear limit, the rods tend to align with the flow and ultimately disperse more due to their anisotropic diffusivities. Results from our Monte Carlo simulations of the particle dispersion are captured remarkably well by a simple theory inspired by Taylor's original work. For long times and large Peclet numbers, an effective one-dimensional transport equation is derived with integral expressions for the particles' longitudinal transport speed and dispersion coefficient. The enhanced dispersion coefficient can be collapsed along a single curve for particles of high aspect ratio, representing a simple correction factor that extends Taylor's original prediction to elongated particles.

physics.flu-dyn↗