arXiv subjects

Robert A. Handler

Publications and source records attributed to Robert A. Handler.

3 recordsLinked to original sources

arXiv2025

Interaction of a Vortex Pair with a Polymeric Fluid Layer

The interaction of vortical structures with boundaries has been extensively studied in Newtonian fluids, where conditions such as no slip walls, free surfaces, or contaminated surfaces dictate whether vortices rebound, dissipate, or generate secondary structures. In this work, we investigate a related but fundamentally different problem: the interaction of a vortex pair with a finite, non uniform layer of polymeric fluid. Numerical simulations employing the finitely extensible nonlinear elastic Peterlin model are used to examine the effects of polymer concentration, relaxation time, polymer layer thickness, and maximum polymer extension on the evolution of kinetic energy and enstrophy. The results show that, while the polymeric fluid dissipates vortical motion, vortex polymer layer interactions can also generate new coherent structures. In particular, the formation of secondary and tertiary vortices coincides with transient increases in kinetic energy, a behavior absent in the Newtonian case. Unlike classical vortex boundary interactions, where the primary vortex survives, we find that under certain conditions it completely dissipates upon interaction with the polymer layer. These findings emphasize that fluids with non-uniform polymer concentrations, act not only as dissipative agents but also as sources of vorticity, extending the traditional view of polymer induced drag reduction and providing new insight into vortex polymer interactions.

physics.flu-dyn↗

arXiv2023

Model for the structure function constant for index of refraction fluctuations in Rayleigh-Benard turbulence

A model for the structure function constant associated with index of refraction fluctuations in Rayleigh-Benard turbulence is developed. The model is based upon the following assumptions: (1) the turbulence is homogeneous and isotropic at or near the mid-plane, (2) the rate of production is in balance with the rate of dissipation, (3) an inertial region exists, and (4) estimates for the rate of dissipation of temperature fluctuations and of turbulent kinetic energy can be made by assuming that the large-scale turbulence is dissipated in one eddy turnover time. From these assumptions, the dependence of the structure function on the geometry, heat flux, and the properties of the fluid is obtained. The model predicts that the normalized structure function constant is independent of the Rayleigh number. To verify the model, numerical simulations of Rayleigh-Benard turbulence were performed using two different approaches: an in-house code based on a pseudo-spectral method, and a finite volume code which employs a model for the smallest scales of the turbulence. The model was found to agree with the results of the simulations, thereby lending support for the assumptions underlying the theory.

physics.flu-dyn↗

arXiv2023

Generation of Laminar Vortex Rings by an Impulsive Body Force

It is shown that laminar vortex rings can be generated by impulsive body forces having particular spatial and temporal characteristics. The method produces vortex rings in a fluid initially at rest, and once generated, the flow field automatically satisfies the boundary conditions and is divergence-free. Numerical simulations and analytical models show that the strength of these rings can be accurately predicted by considering diffusion alone, despite the nonlinear nature of the generation process. A particularly simple model, which approximates the source of vorticity within vertical slabs, is proposed. This model predicts the ring circulation almost as accurately as a model which uses the exact geometry of the source of vorticity. It is found that when the duration of the force is less than a time scale based on the force radius and fluid viscosity, the ring circulation can be predicted accurately using an inviscid model.

physics.flu-dyn↗