Lda Study of Turbulence Characteristics in Vegetated Flows

At the present time the study of vegetation effects on the characteristics of the river’s flow is an important topic of research, due not only to ecological reasons but also to its economic impact. In particular, some authors observe that the ecological systems contribute to human welfare and, therefore they represent a part of the economical value of the planet. The aim of our study is to experimentally investigate the effects of two models of rigid submerged vegetation on the turbulence characteristics of a uniform flow. In particular, the vegetation was modelled with brass cylinders; for each model, the cylinders had the same diameter but different height; the number of cylinders per unit area was the same. Experimental measurements were carried out in a plant set in the Department of Hydraulic, Geotechnical and Environmental Engineering of the University of Naples Federico II. First of all the measurement system was calibrated. The effects of the two models of vegetation were compared one another, either evaluating the roughness values or detecting instantaneous velocities through the use of a Laser Doppler Anemometer system with a Real Signal Analyzer in order to investigate the distributions of the instantaneous velocity statistical moments in ascending order (local mean velocity, standard deviation, skewness, kurtosis). At the end of the experiments, some effects of not similarity between the two models of vegetation were pointed out.