Date of Award
Civil and Environmental Engineering
Biswas, Niharendu (Civil & Environmental Engineering)
Water Resources Engineering.
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In this thesis, detailed experiments are performed to study the effect of the flow depth on turbulent structures in smooth and rough bed open channel flow. When the rough bed is introduced in the shallow flow, the local turbulence near the roughness element intensifies and becomes highly heterogeneous. The model roughness under study consists of a train of two dimensional square ribs spanning the whole length of the channel. The height of the ribs (k) occupy 10-15% of the depth of flow (d) and falls in the category of large roughness. Velocity measurements were conducted using laser Doppler velocimetry (LDV) and particle image velocimetry (PIV) systems. While on the smooth bed, mean velocity scaling in the classical logarithmic format was confirmed from the present experiments, for the deep-flow cases, turbulence quantities were found to be influenced by the free surface. A modified length scale based on a region of constant turbulence intensity is proposed to account for the effect of the free surface. Two-dimensional PIV measurements were made in the streamwise-wall normal plane of the smooth open channel flow at d = 0.10 m and Red = 21,000 to further study the influence of the free surface on the turbulent structures. Proper orthogonal decomposition (POD) and swirling strength analysis were employed to investigate the structures present in the flow. Analysis of the POD reconstructed velocity fields reveals the presence of large-scale energetic structures near the free surface.
Roussinova, Vesselina, "Turbulent structures in smooth and rough open channel flows: effect of depth" (2009). Electronic Theses and Dissertations. 94.