arXiv subjects

Orr Avni

Publications and source records attributed to Orr Avni.

5 recordsLinked to original sources

arXiv2026

Maximal spreading of impacting viscoelastic droplets

Droplet impact and spreading on solid substrates are well understood for Newtonian fluids, yet how viscoelasticity alone modifies the maximal spreading remains unclear. To identify the mechanisms governing the spreading dynamics, we conducted impact experiments and measured the maximal spreading diameter to quantify how fluid elasticity modifies the maximal spreading of impacting droplets. Experiments were performed using fluids within a narrow range of viscosity and surface tension, but with varying relaxation times. For a wide range of conditions, viscoelastic droplets follow a similar behavior as Newtonian ones; however, their maximal spreading diameter is significantly reduced compared with the Newtonian behavior when the Deborah number is of order unity. These observations are rationalized by incorporating the viscoelastic effects into a classical energy balance model. The scaling argument obtained from this model explains the reported reduction in maximal spreading and identifies the range of fluid properties for which the strongest viscoelastic effects emerge.

physics.flu-dyn↗

arXiv2025

Heavy Particle Motion in Rotational Vortices

This study examines the motion of spherical inertial particles in a three-dimensional rotating cylindrical vortex - a simplified model of geophysical flow structures such as oceanic eddies. The analytical vortex formulation enables the isolation of the key mechanisms that govern particle transport in rotating flows. Using Lagrangian particle tracking simulations, we investigate the influence of drag, buoyancy, virtual mass, Coriolis, and Magnus lift forces across a range of particle sizes, densities, and vortex rotation rates. Results show that particle aggregation and periodic stability depend on both particle inertia and flow parameters. Rotational lift forces, though often neglected for spherical particles, become dominant at moderate particle Stokes numbers and introduce slow vertical oscillations in both particle position and spin. The balance of forces determines whether particles settle into stable periodic orbits or escape the vortex. Our analysis reveals unique equilibrium positions that exhibit bifurcations, with multiple or vanishing steady states depending on particle and flow characteristics. Our results demonstrate how particle aggregation and orbital stability stem from the complex coupling between rotational lift, Coriolis, drag, buoyancy, and virtual mass forces. This model may promote informed modeling of dispersed phase transport in marine flows and industrial mixing processes.

physics.flu-dyn↗

arXiv2024

On the early stages of vapor bubble growth: From the surface-tension to the inertial regime

This paper presents a new analytical model for the early stages of vapor bubble growth in superheated liquids. The model bridges a gap in current knowledge by focusing on the surface tension-controlled, near-equilibrium growth regime and its transition to an inertia-controlled regime. A unified analytical model is derived by combining a perturbation method for the initial growth regime with a complementary outer solution to model the subsequent bubble growth rate. The model successfully predicts the initial delay in bubble growth due to surface tension effects. Two non-dimensional parameters govern this delay period: the initial perturbation from the equilibrium radius and the Ohnesorge number at the onset of nucleation. The Ohnesorge number encapsulates the interplay between viscous damping and surface tension forces acting on the bubble during its early growth stages. The analytical solutions presented here allow for quantifying the surface-tension, inertial, and transitional regimes while establishing a simple criterion for estimating the influence of thermal effects on early-stage growth. Our findings emphasize the significance of considering the surface tension delay, particularly for short timescales. The derived analytical solutions and the obtained correlation for surface-tension-induced delay may prove a practical tool and could be integrated into existing models of vapor bubble growth.

physics.flu-dyn↗

arXiv2022

Dispersion of Free-Falling Saliva Droplets by Two-Dimensional Vortical Flows

The dispersion of respiratory saliva droplets by indoor wake structures may enhance the transmission of various infectious diseases, as the wake spreads virus-laden droplets across the room. Thus, this study analyses the interaction between vortical wake structures and exhaled multi-component saliva droplets. A self-propelling analytically-described dipolar vortex is chosen as a model wake flow, passing through a cloud of micron-sized evaporating saliva droplets. The droplets' spatial location, velocity, diameter, and temperature are traced and coupled to their local flow field. For the first time, the wake structure decay is incorporated and analyzed, which is proved essential for accurately predicting the settling distances of the dispersed droplets. The model also considers the non-volatile saliva components, adequately capturing the essence of droplet-aerosol transition and predicting the equilibrium diameter of the residual aerosols. Our analytic model reveals non-intuitive interactions between wake flows, droplet relaxation time, gravity, and transport phenomena. We reveal that given the right conditions, a virus-laden saliva droplet might translate to distances two orders of magnitude larger than the carrier-flow characteristic size. Moreover, accounting for the non-volatile contents inside the droplet may lead to fundamentally different dispersion and settling behavior compared to non-evaporating particles or pure water droplets. Ergo, we suggest that the implementation of more complex evaporation models might be critical in high-fidelity simulations aspiring to assess the spread of airborne respiratory droplets.

physics.flu-dyn↗

arXiv2022

Dynamics of Evaporating Respiratory Droplets in the Vicinity of Vortex Dipoles

A new mathematical analysis of exhaled respiratory droplet dynamics and settling distances in the vicinity of vortical environments is presented. Recent experimental and theoretical studies suggest that vortical flow structures may enhance the settling distances of exhaled respiratory droplets beyond the two-meter distancing rule recommended by health authorities lately. We propose a mathematical framework to study the underlying physical mechanism responsible for the entrapment and subsequently delayed settling times of evaporating droplets and solid particles. A dipolar vortex is considered self-propelling through a cloud of micron-sized evaporating droplets. This configuration might be utilized to approximate an indoor environment in which similar unsteady vortical flow structures interact with exhaled respiratory droplets. We demonstrate the vortex dipole effect on droplet and solid particles settling distances, depending on the evaporation rate, the vorticity of the dipole, and the droplet's initial diameter and location relative to the vortex core. Our theoretical analysis reveals non-intuitive interactions between the vortex dipole, droplet relaxation time, gravity, and mass transfer. The existence of optimal conditions for maximum displacement is suggested, where the droplet entrainment reaches up to an order of magnitude larger than the vortex core length scale. We present a basic model that may be applied for evaluating the spread of exhaled respiratory droplets in vortical environments. Our theoretical study suggests that exhaled respiratory droplets initially at rest can translate to significant distances, hence implying that vortical flow might enhance the transmission of airborne pathogens.

physics.flu-dyn↗