Influence of Form-Induced Shear Stress on Turbulent Kinetic Energy Budget Distributions Above and Within the Flow-Gravel-Bed Interface in Permeable Gravel Bed Stream—a Comparative Study
2021
Ghosh, Mithun | Das, Ratul
Present study aims to illustrate the role of form-induced shear stress on turbulent kinetic energy (TKE) budget distributions in permeable gravel bed streams. In order to achieve the objective of this study, some significant experimental works on turbulent flow characteristics over rough beds are reviewed first and compared with the results of present studies. Uniform gravels (d₅₀ = 4 cm) are arranged randomly in five layers on a 15 cm long open channel. The bed topography and porosity induces spatially heterogeneous flow fields in the near-bed region and to resolve the spatial heterogeneity of flows above and within the flow-gravel-bed interface the traditional time-averaging approach is supplemented by the double-averaging (DA) concept. The form induced shear stress (FISS) depicts significant role in order to obtain total turbulent stress and found to be 40% of the DA Reynolds shear stress (RSS) occurring at the virtual bed level. Also, TKE budget distributions reveal that the TKE production, dissipation and pressure energy diffusion attains maximum values above the virtual bed level and decreases sharply below it. Importantly, the pressure energy diffusion shows a negative magnitude below the gravel crest. Moreover, the TKE dissipation rate is considerably smaller than its production rate above and within the flow-gravel-bed interface.
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