First Advisor
Xiaowei Zhu
Term of Graduation
January 2026
Date of Publication
6-1-2026
Document Type
Thesis
Language
English
Subjects
Direct Numerical Simulation, Dispersion mechanisms, Inertial particles, Preferential concentration, Secondary flows, Urban roughness
Physical Description
1 online resource ( pages)
Abstract
This study employs direct numerical simulation (DNS) to investigate the dispersion of inertial particles in turbulent flow over three-dimensional urban-like roughness at Reτ = 200. Particles with Stokes numbers St = 5, 25, and 100 are tracked over cubic arrays with spanwise spacings Sy from 2h to 32h, where h = δ/8 and δ is the half-channel height, alongside a smooth-wall reference case. The results reveal scale-dependent particle responses characterized by three distinct regimes. First, high-inertia particles (St = 100) align strongly with mean secondary flows, exhibiting organized plumes above roughness elements. Their vertical transport peaks at intermediate spacing (Sy = 8h) due to inertial filtering of turbulent fluctuations. Second, intermediate particles (St = 25) display maximum preferential concentration, with clustering intensity reaching its peak at Sy = 16h. This enhanced clustering is attributed to turbophoretic effects that optimally drive intermediate particles toward the wall. Third, low-inertia particles (St = 5) remain relatively uniformly distributed, responding primarily to small-scale turbulent diffusion. Voronoi analysis quantifies the spatial clustering, confirming that intermediate particles experience the strongest preferential concentration. Spanwise velocity profiles further demonstrate that only high-inertia particles replicate the secondary flow pattern. These findings establish a comprehensive framework linking particle inertia to dominant dispersion mechanisms, providing physical insights for urban air quality management strategies targeting different pollutant size classes.
Rights
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Recommended Citation
Riddle, Rae, "Scale-Dependent Particle Transport over Urban-Like Roughness in Turbulent Flow" (2026). Dissertations and Theses. Paper 7103.