The research will explore sediment dislodgement under the influence of fluctuating hydrodynamic forces for boundaries spanning hydraulically smooth to fully-rough, and flow conditions from laminar to fully turbulent. At the present time, the mean boundary shear stress is widely used as the criterion for identifying the threshold of motion for particles in streams, as well as biological and industrial flows. Unfortunately, the dynamic features of these flows are not adequately captured by such criteria, nor even by models based upon instantaneous hydrodynamic forces. That is, these approaches ignore the time-dependent dynamic aspects of the flow (recently demonstrated by Diplas, Dancey et al. (2008).) The basic premise in this study is that fluctuating forces and associated impulse due to the highly unsteady and dynamic nature of turbulent flow, and grain-induced vortex shedding for both the laminar and turbulent cases, are responsible for sediment transport at near threshold conditions. The research will investigate the scaling behavior of flow structures which are most effective at imparting the necessary impulse. This will be accomplished experimentally, using state-of-the- art time-resolved (>1000 kHz) digital particle image velocimeter measurements simultaneous with dynamic grain surface pressure measurements and non-intrusive grain motion detection.
Intellectual merit: Flow over an erodible boundary is the central problem in earth surface dynamics and is applicable to biological flows and many industrial processes. The process is complex and still poorly understood. The intellectual merit of this research relates to both the advancement of our knowledge and understanding of the phenomena as well as practical predictive capabilities. This research will: Advance our fundamental understanding of the dynamic interplay between fluctuating fluid forces and particle dislodgement and may contribute to the development of new analytical approaches and experimental methods, as well, Identify the flow structures that are most effective in imparting sufficient momentum/impulse to entrain particles, Contribute to the development of a new universal criterion for identifying threshold of motion conditions, Facilitate the development of improved bed load transport equations, especially those using the notion of excess shear stress.
Broader Impact: The research relates to a broad range of societal problems associated with the Earth's Critical Zone and various industrial processes, among them: 1. Dynamics of water processes in the environment. Improvement of existing engineering methods for the design of stable waterways. Discovery of the mechanisms responsible for scour around bridge piers and other structures. Establishment of risk-based methods for preventing the removal of contaminated sediments. Identification of consequences on stream ecology and biology 2. Climate change and Natural Hazards. Prediction of effects on reservoir sedimentation and its life expectancy. Identification of beach erosion mechanisms and implementation of effective protection schemes 3. Industrial processes. Development of improved models for solid phase transport in pipelines. Establishment of better models for removal (flushing) of solid phase contaminates.
