Guangnian Ji | Searcharxiv

arXiv2026

Scale- and Structure-Dependent Fractal Dimensions in a Two-Dimensional Atomizing Liquid Jet

Atomization stretches and folds the liquid-gas interface before fragmenting it into ligaments and droplets, making fractal measures a natural descriptor of the breakup state. We examine this idea in two-dimensional volume-of-fluid direct numerical simulations, VOF-DNS, of a liquid jet with adaptive mesh refinement in Basilisk. Box counting of the full resolved interface does not yield a single scale-independent exponent. Instead, two scaling ranges appear, separated by a crossover near box-counting level Lbox about 7: coarser boxes measure the folded connected jet envelope, whereas finer boxes increasingly sample ligaments, droplets, and nearly smooth local interface segments. Decomposing the interface into detached droplets, ligaments, and the connected main body shows that the relevant effective dimension is structure dependent. Droplets remain near Euclidean at fine scales, ligaments occupy an intermediate level, and the main body carries the largest coarse-scale dimension. This hierarchy persists for liquid Reynolds numbers from 100 to 10000 at fixed gas Weber number 200. Thus, in this two-dimensional VOF-DNS setting, fractal dimension is best interpreted not as a single global exponent, but as a scale- and structure-resolved state variable for interfacial folding and breakup.

physics.flu-dyn↗

arXiv2023

Analysis of Flow Field and Pneumatic Noise of The Flow around Series Cylinder

Noise generation attributed to the flow around a cylinder and its control is of paramount importance in a multitude of engineering applications. In this study, we employ computational fluid dynamics (CFD) coupled with acoustic analogy, complemented by an analysis grounded in vortex dynamics theory, to explore the potential of wavy cylinder shapes in improving aerodynamic performance and mitigating aerodynamic noise. The series cylinder simplified from the aircraft landing gear and elliptical cylinder noise suppression mechanism is analyzed.Our research outcomes clearly indicate that elliptical ylinder designs have a notable impact on aerodynamic performance and noise reduction. Specifically, these designs effectively lower the average drag coefficient and efficiently suppress lift coefficient fluctuations, resulting in an overall reduction in noise production by the elliptical cylinder. To delve into the underlying mechanisms of noise suppression, our study meticulously examines the process of vorticity generation around the elliptical cylinder's surface. This examination yields profound improvements in the distribution of vorticity on the cylinder's surface, along with a remarkable weakening of the boundary vorticity flux and boundary enstrophy flux distribution. These changes result in a notable reduction in vorticity generation near the elliptical cylinder wall.These alterations directly lead to a substantial contraction in the distribution of vortex structures in the wake of the elliptical cylinder, especially affecting large-scale vortex structures.As a result,The elliptical cylinder noise suppression mechanism we propose can effectively reduce aerodynamic noise.

physics.flu-dyn↗