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Production and Dissipation of Turbulent Kinetic Energy in the Roughness Layer

Author(s): Rui M. L. Ferreira; Mafalda Amatruda; Ana M. Ricardo; M′Ario J. Franca; Cristiana Di Cristo

Linked Author(s): Cristiana Di Cristo, Rui M.L. Ferreira, Ana Margarida Ricardo

Keywords: Gravel-sand beds; Turbulent flows; TKE production and dissipation; PIV; LD

Abstract: In turbulent open-channel flows with low relative submersion, mobile bottom boundary and high spatial variability there is little experimental evidence on the budget of TKE. In particular, upscaling TKE characterization with double-average (DA) should be necessary to fully understand the terms of turbulent production. The objectives of the present experimental work are i) to quantify the production and dissipation terms of the equation of conservation of TKE in turbulent open-channel flows with low to moderate submergence, verifying local equilibrium hypothesis ii) to assess the influence of a mobile boundary. To fulfil the objectives, instantaneous velocity data were obtained in two similar flumes with 2D PIV and with LDA. The production terms were computed assuming that, in the absence of buoyancy forces, conversion of mean kinetic energy into TKE corresponds to shear production. The rate of dissipation was computed from the transverse Taylor microscale. The results show that equilibrium between rates of production and dissipation is pushed further up in the water column as the bed mobility becomes important and bedload increases. Wake production terms are non-negligible below the crests of the roughness elements.

DOI:

Year: 2010

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