Title page for ETD etd-82697-195326

Type of Document Dissertation
Author Balakrishnan, Mahalingam III
Author's Email Address mbalakri@vt.edu
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
  • Incipient Sediment Motion
  • Open-Channel Flow
  • Roughness Sublayer
Date of Defense 1997-08-28
Availability unrestricted
The Role of Turbulence on the Entrainment of a Single Sphere

and the Effects of Roughness on Fluid-Solid Interaction

Mahalingam Balakrishnan


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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