Flow around three-dimensional obstacles in boundary layers

An experimental investigation was carried out to study the structure of the flow field around three-dimensional obstacles of different aspect ratios, in two different types of boundary layers. The dimensions of the rectangular block obstacles were chosen to represent generic shapes of buildings. In order to study the flow field around a building structure in a wind tunnel test, the simulation of a boundary layer similar to the atmospheric boundary layer was a crucial issue. For the oncoming flow, a boundary-layer profile representing a suburban site was adopted in the present investigation. The studies were performed using different kinds of flow visualisation techniques and a laser Doppler anemometry (LDA) system, specially developed for wind tunnel applications and designed to provide a high spatial resolution. The results of the experiments showed the dependence of the flow structure around the obstacle on its aspect ratio, the angle of attack, the Reynolds number, and the type of boundary layer. Detailed quantitative information of turbulence parameters in the vicinity of the obstacle was attained. In addition, all data were compiled to schematic sketches of the flow topology around three-dimensional obstacles.