Experimental investigation of wake flow field and wind comfort characteristics of fractal wind fences

Wind fences are frequently utilized in many areas from agriculture to traffic safety in order to provide a sheltered region behind. The conventional geometry of wind fences are usually porous with circular or rectangular holes. Recent studies on fractal/multiscale grid geometries, i.e. a geometry that consists of smaller scales that are copies of the whole, show interesting results, indicating a potential towards using these types of grids as wind fences. Thus, the main purpose of this study is to investigate the performance of fractal grids as wind fences. For this purpose, four different types of wind fences, three of which have fractal grids, all having the same porosity ratio of 40%, are tested in a wind tunnel. Results of the two-dimensional PIV measurements downstream of each fence are presented. Comparisons of the details of the wake flow structure as well as quantitative comparisons of wind comfort and shelter characteristics up to 10H downstream of fences, where H is the fence height, are also presented. Results show that the jet-wake-wall interactions within the near wake of the fences have a major impact on wind comfort characteristics further downstream. These interactions can potentially be manipulated by custom designing fractal grid fences based on given wind comfort requirements in order to obtain required mean flow and sheltering characteristics.