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You are here : eLibrary : IAHR World Congress Proceedings : 36th Congress - The Hague (2015) ALL CONTENT : Sediment management and morphodynamics : Mechanics of particle entrainment from a rectangular cavity
Mechanics of particle entrainment from a rectangular cavity
Laboratory experiments are conducted in an open-channel flume to investigate the mechanics of particle entrainment from
a rectangular cavity under various test conditions. The motivation of this study is the sediment entrainment from gaps
between the large concrete blocks used in grade control structures, which are constructed to prevent pier-scour during
typhoon-induced floods in Taiwan. Video recordings of particle movement in the cavity reveal that particle entrainments
are significantly influenced by the random fluctuations of the flow field; with particles being entrained at widely varying time
durations ranging from as short as 10 seconds to as long as 10 minutes and beyond, even under the same experimental
condition. Particle trajectories inside the cavity are observed to be predominantly affected by the cavity aspect ratio and
the initial release position of the particle. This is because the flow field undergoes significant changes with different cavity
dimensions, causing the particle to be subjected to different flow structures depending on its position in the cavity. The
presence of the rectangular cavity in the open channel leads to a sudden geometrical expansion, causing the 2-
dimensional flow to transition into a 3-dimensional flow in the cavity. The new flow field affects both the lateral and vertical
movements of the particle; and eddies that form at the downstream cavity edge are observed to be the agent primarily
responsible for directly entraining the particle out of the cavity. In summary, the mechanics of particle entrainment from a
rectangular cavity in an open channel flow involves interaction of the particle with the flow field and the random
fluctuations in the flow. When a particle experiences a favorable, albeit sporadic sequence of events, entrainment of the
particle occurs.
File Size : 342,083 bytes
File Type : Adobe Acrobat Document
Chapter : IAHR World Congress Proceedings
Category : 36th Congress - The Hague (2015) ALL CONTENT
Article : Sediment management and morphodynamics
Date Published : 13/08/2015
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