In turbulent open-channel °ows with low relative submersion, mobile bottom boundary and high spatial vari- ability 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 °ows with low to moderate submergence, verifying local equilibrium hypothesis ii) to assess the in°uence of a mobile boundary. To ful¯l the objectives, instantaneous velocity data were obtained in two similar °umes 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.

Production and dissipation of turbulent kinetic energy in the roughness layer.

DI CRISTO, Cristiana
2010

Abstract

In turbulent open-channel °ows with low relative submersion, mobile bottom boundary and high spatial vari- ability 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 °ows with low to moderate submergence, verifying local equilibrium hypothesis ii) to assess the in°uence of a mobile boundary. To ful¯l the objectives, instantaneous velocity data were obtained in two similar °umes 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.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11580/5321
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