Quantifying unsteady shear effects on clay-loaded media: stability and surface roughness implications

Clay-laden flows play a significant role in shaping rivers, estuaries, coastal systems, and deep-sea environments by controlling erosion, sediment movement, and water quality. However, despite their environmental and engineering importance, the influence of clay on flow behavior remains poorly understood. This award will explore how clay interacts with fluid motion across a range of real-world conditions by studying how these flows behave under controlled high-frequency oscillations. Laponite, a synthetic clay that forms a transparent suspension in water, will be used to enable researchers to observe and measure particle motion and turbulence development using advanced optical techniques. The project will lead to new models for predicting sediment transport, erosion, and flow stability in both natural systems and industrial settings. The findings can improve flood risk assessments, water quality monitoring, and the design of hydraulic structures. The award will also support hands-on learning for students in engineering and environmental science, encouraging interest in research careers and helping train the next generation of scientists and engineers in fluid dynamics and sustainability. This award focuses on the fundamental physics of clay-laden flows subjected to transitional flow conditions, where turbulence develops under intense, time-dependent shear driven by high-frequency, small-amplitude oscillations. The project aims to systematically quantify how clay concentration alters the onset, structure, and evolution of turbulence in such flows. Using a custom-designed laboratory flume, the study will explore three primary regimes: (1) the transition from laminar to turbulent flow as a function of clay concentration and oscillatory shear, (2) the development and scaling of boundary layers over smooth surfaces, and (3) the influence of organized and random roughness on turbulence modulation in clay-laden boundary layers. Experimental results will be used to derive functional relationships linking turbulence characteristics to key control parameters: clay concentration, shear frequency, amplitude, and surface roughness. Emphasis is placed on identifying instability mechanisms, characterizing coherent structures, and quantifying energy redistribution across flow scales and regimes. These findings will inform predictive scaling laws for transitional clay flows and support models of sediment transport and boundary-layer behavior in engineered and natural systems. By bridging fundamental fluid mechanics with environmental and engineering relevance, this award will offer critical insights applicable to natural sediment-laden flows, infrastructure resilience, slurry transport systems, and water quality management across multiple scales. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.