Boundary layer characteristics just above sub-urban roughness
Dutta, Satya Ranian
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With regard to the reliable design of distribution lines (less than 60 ft) and other structures that stand just above the suburban roughness, it is very important to accurately study the complex turbulence structures in the region of suburban roughness sublayer. In this study, it has been found that the profiles of mean wind velocity, turbulence intensity and integral length scale parameters (longitudinal, lateral, and vertical) are not exactly the same as those used in ASCE 7, which considers the ideal case of turbulence above open terrain or well above the roughness. To accomplish this, wind tunnel experiments were carried out in Texas Tech University's wind tunnel facility and then the data was analyzed to determine the variation of turbulence and gust size just above the roughness. Very close simulations of open and suburban terrain were accomplished by respectively laying carpet and carpet plus 12 house models (in 4 rows) in the upstream section of the wind tunnel. To determine the integral length scales, cross correlation and auto correlation methods were employed with the help of Math CAD software. The profiles of different parameters were determined with respect to height and surface roughness. Also, to determine the effect of an abrupt change of terrain, a single row of 3 house models was placed in front of the line of measurement and the corresponding test data analyzed. It has been primarily concluded that the suburban roughness sublayer turbulence affects the gust effect factors which in turn affect the design wind load on distribution lines and the other structures that stand just above the suburban roughness.