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Analysis of 3 Rd Order Moments on a Natural Vegetated Flow

Author(s): Silvia Saggiori; Sergio Rita; Rui M. L. Ferreira; Mario J. Franca

Linked Author(s): Mário Franca, Rui M.L. Ferreira

Keywords: No Keywords

Abstract: Mixing and transport processes occurring in open channel flows still pose important research challenges. The understanding of their dynamics, namely in what concerns interaction of hydrodynamic and environmental variables, is essential to predict accurately mass transfer processes (important to pollution dispersion and other water quality issues), momentum transfer processes (important to flow resistance issues), and sediment transport (important to the design of stable channels). The presence of vegetation induces extra complexity on the turbulent flow structure due to production at stems and leaves. In such flows, turbulence production is a consequence of local shear layers caused by flow separation at the vegetation body. Hence, coherent movement detected within the water column is intrinsically conditioned by several local effects, namely: riverbed, vegetation stems and vegetation leaves. The objective of this study is to evaluate how third-order velocity moments vary throughout the water column on a vegetated river. To accomplish the proposed objective, AcousticDopplerVelocimetry (ADV-Vectrino) measurements were performed along several vertical profiles on a natural river populated by submerged and flexible vegetation. The use of ADV in fieldwork allows resolving 3D turbulent process within the vegetation with a frequency of 100 Hz. Time-average velocities, Reynolds stresses, probability density function of fluctuating velocities and third-order velocity moments are herein shown and discussed.


Year: 2012

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