Flow around cylindrical towers : the stabalising role of vertical ribs

[摘要] The aim of this thesis is to study the stabilising effect which vertical ribs may have on a tallcylindrical 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 offlow regimes which exist for flow around a circular cylinder and these flow regimes, togetherwith their characteristics, are described. Various threats to the Solar Chimney are identifiedand will be investigated. The natural shape and strength of the Saguaro Cactus leads to theinvestigation of vertically ribbed cylinders.Experimental wind tunnel tests are performed in Tokyo, Japan to obtain external pressuredistributions. A smooth cylindrical model, as well as two different configurations of verticallyribbed cylinders are tested. These external pressure distributions are numerically integrated inorder to obtain calculated drag coefficient values for the cylinders.The drag coefficients for a smooth cylinder and cylinders with vertical ribs are obtainedexperimentally by means of total drag force measurements. These tests were performed in thewind tunnel at the University of Stellenbosch. The effect of aspect ratio of a smooth cylinderis also addressed.Computational Fluid Dynamics (CFD) analyses are carried out using the CFD softwareprogram, FLUENT. Both the drag coefficient and the external pressure distributions wereinvestigated in this way. The differences between theoretical conditions and those of real lifeconditions of a smooth cylinder are discussed.The report ends by concluding the stabilising effect of vertical ribs on tall cylindricalstructures and how these ribs may eliminate some of the present threats to the proposed SolarChimney.

[发布机构] Stellenbosch University