Entrainment Phenomenon across Scales: From Micro Cough Aerosols to Macro CO₂ movement

This thesis investigates entrainment phenomena across multiple spatial scales, focusing on two distinct but interconnected applications: respiratory droplet transport in cough jets and CO$_2$ mixing in wind turbine wakes. Through comprehensive experimental approaches, this research advances our understanding of how entrainment processes govern fluid transport across these scales while contributing to solutions for pressing environmental and public health challenges.

The first study develops and validates a novel cough simulator for respiratory disease research. Using a subwoofer-driven aerosol chamber controlled by a modified gamma-probability-distribution function, the device generates pulsatile airflow that accurately mimics human coughs. Extensive particle image velocimetry and flow visualization measurements demonstrate the simulator's capability to produce repeatable cough profiles with peak velocities ranging from 2.99 to 38.47 m/s and peak velocity times from 8.75 to 60.00 ms. The device's innovative design offers precise control over key flow parameters while maintaining accessibility through the use of off-the-shelf components.

The second study examines entrainment effects in wind turbine wakes through wind tunnel experiments investigating CO$_2$ transport. Using a scaled wind turbine model and spatial CO$_2$ concentration measurements, this work provides experimental validation of computational predictions regarding turbine-induced mixing. Experiments conducted at two free-stream velocities (4 m/s and 10 m/s) reveal significant differences in CO$_2$ concentration profiles between cases with and without the turbine present, particularly in the near-wake region where turbine-induced mixing most strongly influences vertical redistribution of CO$_2$.

This research demonstrates how careful experimental characterization can illuminate entrainment mechanisms from micro-scale droplet transport to macro-scale atmospheric mixing, while providing practical applications for addressing contemporary challenges in disease transmission and atmospheric transport processes. The findings contribute to both fundamental fluid dynamics understanding and applied solutions for public health and environmental management.