This dissertation presents the aerodynamic characteristics of rectangular cylinders with various corner cuts in the uniform flow of different attack angles. To accomplish this objective, a series of wind tunnel tests are performed for the various topics in the uniform flow as follows.
At first, the aerodynamic characteristics of a square cylinder with various corner modifications under different attack angles is investigated. It is also considered that the aerodynamic characteristics of a square cylinder with various corner cutting shapes under different attack angles. From the test results, the corner modifications are effective to the galloping phenomenon at relatively small attack angles. Especially, corner cut method shows best behavior for the galloping phenomenon. However, vortex-induced vibration occurs at relatively small wind velocity, and has sharp peak at a relatively high attack angle. It is observed that the aerodynamic behaviors of the test models are nearly dominated by the upwind shapes of the models, i.e., the separation from upwind corners of the models.
Then, the experiments on the blockage effect and determination of Strouhal number are performed. A parametric study on the wind tunnel blockage effect on the wind-induced dynamic characteristics of two test models, i.e., the square and the square with corner cut, is presented. From a series of tests, it has been concluded that the wind-induced dynamic characteristics of test models are in good agreements in case of models with up to 10% blockage ratios and the models with up to 10% blockage ratios can be treated as the same group which behaves similarly.
A new approach is suggested to determine the Strouhal number of rectangular cylinders in a uniform flow based on the aerodynamic behaviors of the body. The validity of the proposed method is evaluated by comparing with the results obtained by previous studies. Therefore, it is concluded that the new method is as good as any previously suggested methods to obtain the Strouhal number.
Finally, the aerodynamic characteristics of rectangular cylinders with various corner cuts under various attack angles is presented. From a series of wind-induced vibration tests, it is discussed that the aerodynamic behaviors of rectangular cylinder with corner cuts and the determination of the optimal corner cut size. The effect of corner cut on the aerodynamic stability for the galloping phenomenon is clear and increases as the attack angle is increased. However, the effect of corner cut on the stability for the vortex?induced vibration are not so large as the case of galloping phenomenon but specific cutting ratios are effective to reduced the amplitude of vortex-induced vibration. Especially, the torsional mode vibrations, i.e., flutter and vortex-induced vibration, can be successfully restrained when the optimal corner cut sizes are introduced to the original section. The effective and ineffective corner cut size can be determined by the wind-induced vibration tests.
Then, the experiments on the variation of Strouhal number and flow visualization are performed to investigate the aerodynamic characteristics of rectangular cylinders with various corner cuts. When the optimal corner cut size is introduced to the original section, Strouhal number has larger values than those of other corner cut sizes throughout all test models. It means that the flow separation of the body is restrained when the effective corner cut size is used, and it results in an increase of Strouhal number. From a series of flow visualization test, it is verified that the separation from upper and lower side of the model is almost restrained. This means that the separation starts from the first edge of corner cut and completely reattaches to the second edge generated by corner cut, thus lead to the restraint of the galloping and vortex-induced vibration phenomenon. These all test results correspond well with observations in the wind-induced vibration test and the variations of Strouhal number.
