Physical Explanation and Modeling of Wind and Water Dynamics

My study shows that even a small number of infected individuals who travel between communities—what we call “geographical spreaders”—can dramatically influence how a disease spreads. Using a mathematical model, we found that just 1–10% of mobile infected people can speed up the outbreak and create organized patterns like waves or hotspots in places far from the original source. These findings highlight that movement—how far and how often people travel—can be just as important as infection rates when it comes to understanding and controlling outbreaks. Even if most people stay put, a few movers can reshape the entire course of an epidemic.

Epidemiology and Fluid Mechanics

Turbulence and the Wall

A fundamental problem in fluid mechanics is explaining energy dissipation in turbulent flows due to friction at boundaries (or wall friction). Progress on this issue is becoming urgent given the substantial economic implications of transporting oil and methane gas in pipelines across entire continents. Traditional analysis for understanding this phenomenon has and continues to rely on empirical methods such as the Nikuradse/Moody diagrams developed approximately a century ago. These diagrams describe the friction factor as a function of Reynolds number and relative roughness. This work has derived a fundamental physical explanation from turbulence physics. This advancement has unified the Nikuradse curves into a single curve, providing a novel explanation for friction loss based on the turbulence energy spectrum and effectively resolving many aspects of this problem.

Published in Physics of Fluids, 2021

Moving beyond boundary layer hydrodynamics, this research has probed how boundary roughness affects the flow structure and, consequently, the bulk flow properties' that impact natural systems.It developed an asymmetric eddy diffusivity model for vegetated flows and formulated a universal velocity distribution equation through asymptotic analysis and applied mathematics. These analytical results agreed with published measurements across several studies. Moreover, recent technological innovations such as floating treatment wetlands offer environmentally friendly solutions for contaminant removal and wastewater treatment, yet their efficiency has not been extensively studied from a physical standpoint. This work addresses this gap by employing computation fluid dynamics based numerical solutions to a reactive model that quantifies the absorption of contaminants by vegetation. It derived an approximated equation for estimating contaminants' removal efficiency in wetland flows linking microscale physics with bulk scale observations, which correlates well with empirical data from field measurements.

Published in Environmental Research Letters, 2019

Turbulence and the Vegetation

Published in Geophysical Research Letters, 2024

Turbulence and Sediments

This work introduced one of the first models for sediment settling velocity in turbulent flows using perturbation solutions. Traditional studies of suspended sediment concentration typically assume that sediment particles' settling velocity in turbulent flows is equivalent to that in still water. However, my work shows that turbulence reduces settling velocity due to the Basset history force and virtual mass effects. This finding addresses recent inconsistencies with findings from the turbulent Schmidt number, unresolved since Rouse's formulation over a century ago. Expanding upon sediment settling, it derived a comprehensive equation for suspended sediment concentration in turbulent flows, encompassing the full spectrum of turbulent eddies from bulk length scale to the smallest scales (Kolmogorov length). Unlike traditional models that use a mixing length representation for sediment diffusion, my proposed approach accounts for all turbulent scales. This systematic analysis reveals the dependency of sediment concentration on Reynolds number and sediment properties, positioning Rouse's equation as a special case applicable only when turbulence is limited to local transport ranges.

currently under review for Physical Review Letters, 2025

Sediment Carrying Capacity From Turbulence Theory

Assessing channel vulnerability to scouring and deposition is crucial for effective climate solutions. While it is well-understood that these processes are driven by sediment motion, a theoretical linkage between sediment physics and river-scale observations has been lacking. This gap has persisted despite the existence of numerous numerical and empirical models. This work derived a universal prediction formula that elucidates the sediment carrying capacity of turbulent flows, starting from microscale turbulence equations such as the Turbulent Kinetic Energy (TKE) and shear stress budget equations. The resultant formula, which spans 5 orders of magnitude of historical data, offers immediate utility in engineering applications for scouring and deposition structures, thereby enhancing the safety and economic stability of downstream communities.

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