Field study of the flow behind single and double row herbaceous windbreaks

Field experiments in the Argentinean Pampas on strong wind days (pampero) have been carried out to investigate aspects of the wind sheltering ability on single and double-row field shelterbelts of Triticale) inserted in wheat plantations (Buck Charrua variety). In the present experiments hot-wire anemometry and continuous wavelet transform analysis were used to describe turbulent features of a relatively small wake region near the shelterbelt 0.5<x/H<3 in which we have found significant variations in the distributions of mean velocities, autocorrelation, power density spectra, turbulence intensity, skewness and kurtosis. The purpose of this study is to examine aspects of the fine structure of turbulence in a highly sheltered region of a wheat plantation protected by other inserted fast growing wheat species. We have analyzed the influence of the width of an herbaceous barrier by simply adding a 15 cm parallel downwind shelterbelt of similar characteristics in the turbulence processing ability of the oncoming wind. We have also focused on the analysis of the sheltering ability of the corresponding wake flows and have examined the penetration phenomena of the outer large-scale structures into the plantation. The reported results strengthen the evidence that descending vertical transport of upstream turbulence contained within the upper external flow into the upper level of the highly protected shelterbelt adjacent region is more important than horizontal bleed flow through the shelterbelt.