Investigation of the turbulent flow beneath an ice block using particle image velocimetry
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Date
2020
Authors
Ahmed, Tanzim
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Abstract
Transported ice blocks can contribute to the development of river ice jams leading to flooding, which has social, economic and ecological impacts on different parts of the northern hemisphere. The moving ice blocks can either be entrained into the flow or halted by an intact ice cover. Understanding the flow physics beneath an ice block is critical for understanding the stability of ice blocks, which is important for river ice jam development and the design of river ice control works. The present study used particle image velocimetry to analyze the flow field beneath an ice block. A 0.025 m thick rectangular acrylic sheet was used to simulate an ice block and detailed velocity measurements conducted beneath it for various approach Froude number and thickness-to-depth ratios (t/h). The flow field in the recirculation, reattachment regions and some selected locations after the reattachment beneath the block were evaluated.
Results showed that, the higher the Froude number and t/h ratio, the greater the flow separation at the leading edge of the block resulting in greater reattachment length beneath the ice block. This is important, as it is known that flow separation at the leading edge causes a pressure reduction that can destabilize the blocks. The mean velocity profile, the turbulence intensity profile and the Reynolds shear stress profile at some selected locations beneath the block were analyzed. The analysis suggested that the mean velocity, the turbulence intensity and the Reynolds shear stress were greatly enhanced by increasing Froude number and t/h ratio within the recirculation region and started to decrease after the recirculation region. This finding supports the breakup of large scale vortical structures dominating the recirculation region formed beneath the ice block due to the flow separation at the leading edge. The results also demonstrated that the presence of an ice block in a channel could alter the flow field locally from open water conditions.
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Keywords
Turbulent flow, Ice block, Particle image velocimetry