Flow around cylindrical towers : the stabalising role of vertical ribs
Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2006.
The aim of this thesis is to study the stabilising effect which vertical ribs may have on a tall cylindrical structure, with the focus on the proposed Solar Chimney. The report begins with a brief introduction to the Solar Chimney concept. A study is made of flow regimes which exist for flow around a circular cylinder and these flow regimes, together with their characteristics, are described. Various threats to the Solar Chimney are identified and will be investigated. The natural shape and strength of the Saguaro Cactus leads to the investigation of vertically ribbed cylinders. Experimental wind tunnel tests are performed in Tokyo, Japan to obtain external pressure distributions. A smooth cylindrical model, as well as two different configurations of vertically ribbed cylinders are tested. These external pressure distributions are numerically integrated in order to obtain calculated drag coefficient values for the cylinders. The drag coefficients for a smooth cylinder and cylinders with vertical ribs are obtained experimentally by means of total drag force measurements. These tests were performed in the wind tunnel at the University of Stellenbosch. The effect of aspect ratio of a smooth cylinder is also addressed. Computational Fluid Dynamics (CFD) analyses are carried out using the CFD software program, FLUENT. Both the drag coefficient and the external pressure distributions were investigated in this way. The differences between theoretical conditions and those of real life conditions of a smooth cylinder are discussed. The report ends by concluding the stabilising effect of vertical ribs on tall cylindrical structures and how these ribs may eliminate some of the present threats to the proposed Solar Chimney.