Type of Document Dissertation Author Balakrishnan, Mahalingam III Author's Email Address email@example.com URN etd-82697-195326 Title The Role of Turbulence on the Entrainment of a Single Sphere and the Effects of Roughness on Fluid-Solid Interaction Degree PhD Department Mechanical Engineering Advisory Committee
Advisor Name Title Brown, Eugene F. Diplas, Panayiotis Ng, W. F. Pierce, Felix J. Dancey, Clinton L. Committee Chair Keywords
- Incipient Sediment Motion
- Open-Channel Flow
- Roughness Sublayer
Date of Defense 1997-08-28 Availability unrestricted AbstractThe Role of Turbulence on the Entrainment of a Single Sphere
and the Effects of Roughness on Fluid-Solid Interaction
Incipient motion criterion in sediment transport is very important, as it defines the flow condition
that initiates sediment motion, and is also frequently employed in models to predict the sediment
transport at higher flow conditions as well. In turbulent flows, even a reasonably accurate
definition of incipient motion condition becomes very difficult due to the random nature of the
turbulent process, which is responsible for sediment motion under incipient conditions. This work
investigates two aspects, both of which apply to incipient sediment transport conditions. The first
one deals with the role of turbulence in initiating sediment motion. The second part deals with the
nature of sediment-fluid interaction for more general and complex flows where the number of sediment
particles that form the rough surface is varied.
The first part of this work that investigates the role of turbulence in initiating sediment motion,
uses a video camera to simultaneously monitor and record the sediment (glass ball) motion and
corresponding fluid velocity events measured by a three-component laser Doppler Velocimeter (LDV).
The results of the single ball experiment revealed that the number of LDV flow measurements increase
dramatically (more than four folds) just prior to the ball motion. The fluid mean velocity and its
root-mean-square (rms) values also are significantly higher than the values that correspond to the
flow conditions that yield no ball motion.
The second part of the work, investigation of the fluid-sediment interaction, includes five tests
with varying number of sediment particles. In order to understand the nature and extent of fluid-solid
interaction, velocity profile measurements using the 3-D laser system were carried out at three locations
for each of these five cases. Plots of mean velocities, rms quantities located the universal layer at about
1.5 ball diameters above the porous bed. However, at higher sediment particle concentrations, this distance
reduced and the beginning of the universal layer approached the top of the porous bed.
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