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- Title
Streamwise Turbulence Modulation in Non‐Uniform Open‐Channel Clay Suspension Flows.
- Authors
de Vet, M. G. W.; Fernández, R.; Baas, J. H.; McCaffrey, W. D.; Dorrell, R. M.
- Abstract
Cohesive sediment particles are ubiquitous in environmental flows. The cohesive properties of clay promote the formation of clay flocs and gels and relatively small suspended clay concentrations can enhance or suppress turbulence in a flow. Furthermore, flows are naturally non‐uniform, varying in space and time, yet the dynamics of non‐uniform open‐channel clay suspension flows is poorly understood. For the first time, the adaptation time and length scales of non‐uniform clay suspension flows were quantified using novel experiments with spatially varying but temporally uniform flow. Different levels of turbulence enhancement and attenuation were identified as the flow decelerates or accelerates. Results highlight that decelerating clay suspension flows crucially have a longer adaptation time than accelerating clay suspension flows. This is explained by the longer timescale required for the formation of bonds between cohesive particles in turbulence attenuated flows after deceleration than the rapid breakdown of bonds in turbulent flows after acceleration of clay suspension flows. This hysteresis is more pronounced for higher concentration decelerating flows that pass through a larger variety of clay flow types of turbulence enhancement and attenuation. These different adaptation time scales and associated clay flow type transitions are likely to affect clay flow dynamics in a variety of fluvial and submarine settings. Plain Language Summary: Flows in natural environments, such as rivers, estuaries, seas, and oceans, can transport sediment in suspension. The suspended sediment can increase or decrease turbulence in a flow, depending on the sediment concentration. Clay has the ability to form bonds between the individual particles and therefore even small concentrations are sufficient to alter turbulence levels in a flow. The amount of alteration of turbulence is known for uniform, constant flow conditions, but in natural environments, flows are often non‐uniform. For example, flow variations can occur due to changes in river width or bed slope. The influence of these variations on clay suspension flows is unknown. New physical experiments were conducted where clay suspension flows were decelerated and accelerated. As the flow decelerates, turbulence in the flow is reduced and bonds between the suspended clay particles are established. Turbulence increases as the flow accelerates and clay bonds are broken. Decelerating flow requires more time to adjust to changes in velocity than accelerating flow, as establishing the bonds between clay particles requires more time than breaking them. This means that, especially for the decelerating flows, the influence of a change in velocity is noticeable further downstream. Key Points: Comparable to uniform flow, the combination of flow velocity and clay concentration influences the clay flow type in non‐uniform flowsAccelerating clay‐laden flows adapt faster to velocity changes than decelerating flows; breaking clay bonds is easier than establishing themAdaptation timescales grow with clay concentration for decelerating clay‐laden flows passing through a larger variety of clay flow types
- Subjects
TURBULENCE; CLAY; SEDIMENT transport; NON-uniform flows (Fluid dynamics); TRANSITION flow; PARTICLE acceleration
- Publication
Journal of Geophysical Research. Earth Surface, 2023, Vol 128, Issue 8, p1
- ISSN
2169-9003
- Publication type
Article
- DOI
10.1029/2022JF006781