IAHR, founded in 1935, is a worldwide independent memberbased organisation of engineers and water specialists working in fields related to the hydroenvironmental sciences and their practical application. Activities range from river and maritime hydraulics to water resources development and ecohydraulics, through to ice engineering, hydroinformatics, and hydraulic machinery.





EVALUATION OF INTEGRAL LENGTH SCALE FROM EXPERIMENTAL FROM EXPERIMENTAL DATA IN A FLOW THROUGH SUBMERGED VEGETATION 
Author : 
PAOLA GUALTIERI , SERGIO DE FELICE , VITTORIO PASQUINO & GUELFO PULCI DORIA , 
The interaction between flow and vegetation is a complex topic. Effects of vegetation on turbulent characteristics can be stressed through experimental measurements. One of the main concerns in turbulence studies is the estimate of temporal and, if possible, spatial characteristics of the existing eddies in the flow. Possibly most easy is the evaluation of the integral timescale of turbulence defined with the use of the autocorrelation function R(t) derived by the analysis of time series collected in fixed positions. The transformation from temporal characteristics of the signal to spatial characteristics can be made by means of the Taylor hypothesis of the ?frozen turbulence?, which is applicable if the intensity of the turbulence of the flow is small. Generally, the autocorrelation function of the longitudinal velocities assumes the shape of curve rapidly decaying to its first zerocrossing, after which an alternation of positive and negative values may be evident. In these cases this characteristic point determines the time lag. In other cases the determination of the integration domain could be not straightforward. In particular, the domain of the autocorrelation function from experimental data is finite, and there is some uncertainty on how best to define the integration domain. Sometimes the integral timescale is assumed corresponding to the time lags at which R(t) drops to 1/e. In this paper the results of experimental studies aimed to the recognition of Eulerian integral length scale in channel with simulated woody vegetation, are discussed. The model of vegetation consisted of regular arrays of stiff vertical cylinders with variation in cylinders density. Two measurements locations were considered. In order to measure instantaneous velocities an LDA system was used. A software was developed to evaluate autocorrelation functions. n The integral timescales were assumed corresponding to the time lags at which R(t) drops to 1/e , testing different values of the exponent n. Eulerian integral length scales were evaluated through Taylor?s hypothesis. Their distributions suggest n that, increasing n, the time lag 1/e corresponds to larger integral length scales and measuring location and cylinders density affect Eulerian integral length scales.

File Size : 
416,575 bytes 
File Type : 
Adobe Acrobat Document 
Chapter : 
IAHR World Congress Proceedings

Category : 
36th Congress  The Hague (2015) FULL PAPERS

Article : 
THEME 2 HYDROENVIRONMENT

Date Published : 
18/04/2016 







