MEAN FLOW AND TURBULENCE STRUCTURE OVER DUNES WITH SUPERIMPOSED SMALLER BEDFORMS

摘要

This work presents results of an experimental project aimed at investigating the meanrnand turbulence structure induced by small dunes superimposed over two-dimensionalrnbedforms, that represent field observations in a 1:30 scale physical model of thernParaná River, Argentina. An acoustic Doppler velocimeter (ADV) is used to measurernthe three components of velocity at 25 Hz. Velocities were sampled at a total of 16rnverticals, with approximately 14 points in each vertical, and having a sampling lengthrnof 3 minutes each, allowing thus for an excellent spatial and temporal resolution ofrnthe flow domain. Processing of the data allowed for the computation of local verticalrnprofiles of mean velocity, Reynolds stresses, turbulence intensities, turbulent kineticrnenergy, etc. as well as the estimation of spatial averages over a wavelength of thernlarger bedform and the computation of relative contributions of the different quadrantsrnto the total Reynolds stress. Drag coefficients were estimated that coincide withrnreported values in the literature. Furthermore, the spatial structure of the turbulentrncoherent events (ejections and sweeps) along the dune wavelength is investigated,rnand the development of a roughness sublayer is characterized.