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Environmental flows form the basis of processes that span sediment transport in rivers, drag reduction in pipelines, and the evolution of severe atmospheric vortices. Despite significant efforts to address related phenomena, a predictive, mechanistic description of how particles, non‑Newtonian carrier fluids, and coherent vortical structures interact across scales remains an open problem. This dissertation addresses key gaps through three interrelated laboratory investigations. The first study examines the collective settling of sphere particles over a broad range of Galileo numbers in both homogeneous and two‑layer stratified fluids. High‑inertia conditions promote wake‑driven path instabilities and lateral dispersion, whereas viscous dominated regimes yield rectilinear descent. Ensemble measurements reveal that particle proximity suppresses drag relative to isolated behaviour, while crossing a density interface induces a transient slowdown governed by entrainment‑driven buoyancy forces. Pair‑dispersion statistics transition from ballistic to super‑diffusive growth below the interface, and mixed‑density arrays exhibit pronounced parachute‑like clustering, demonstrating the sensitivity of settling to buoyancy contrast and initial arrangement. The second study probes turbulence modulation in wall‑bounded flows laden with dilute polymeric and clay suspensions. Even trace concentrations of Xanthan gum or Laponite attenuate high‑wavenumber fluctuations and substantially reduce wall shear stress. The clay suspension further displays time‑dependent enhancement of drag reduction as its microstructure ages, confirming that weak viscoelasticity and thixotropy provide passive spectral filtering of near‑wall turbulence. Building on these insights, the third study constitutes a first step toward coupling particulate matter with tornado‑like vortices. A customized vortex simulator demonstrates that vortex structure, momentum distribution, and turbulent kinetic energy are all influenced by the swirl ratio, shaping the flow characteristics that ultimately govern saltation and debris entrainment in atmospheric storms. The experiments and setups establish a multiscale framework that links inter‑particle hydrodynamics, rheology‑controlled turbulence, and coherent‑vortex structure. The scaling laws and mechanistic insights derived herein advance predictive modeling and inform strategies for sediment management, drag reduction, and hazard mitigation in natural and engineered environmental systems.
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