Effects of the twisting aloft wind on the wind fields around a high structure in the atmospheric boundary layer

• Main Authors: Da-MingLi, 李達銘
• Other Authors: Chung Fang
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/72357250225604329248

碩士 === 國立成功大學 === 土木工程學系碩博士班 === 100 === The wind fields around high-altitude structures inside the atmospheric boundary layer and the induced dynamic loads in the structures are investigated by using the numerical simulations based on the Fluent package, in which the focus is on the twisting effects of winds caused by the Coriolis force. The structure models employed in the numerical simulations are rigid, cylindrical and square columns with/without shrinking cross-sections with altitude. A number of test simulations have been carried out to identify the shedding frequency and the Strohal number of the ka ̀eman ̀ vortex sheet behind a square column, on which the accuracy of the numerical model has been verified. Results of the numerical simulations are discussed in the following three categories. (1)The steady-state wind fields around a cylindrical column remain symmetrical along the incoming wind direction, which shifts its orientation gradually to the right due to the Coriolis force, as the altitude increases. On the contrary, such a situation does not prevail for square columns: the wake region increases as the altitude increases. For cylindrical/square columns with shrinking cross-sections with altitude, the wake regions near the top of the columns are reduced significantly. (2)When compared to the along/cross wind drags on the cylindrical column from no-twisting incoming winds, the induced along-wind drag due to the twisting aloft wind is nearly the same as before, however, the cross-wind drag increases to about 50% of the along-wind drag. In the cases of square columns, the induced along/cross wind drags are much higher than their counterparts for cylindrical columns. (3)The wind-induced torques on the cylindrical/square columns are much smaller than the drags, either in the along-wind or cross-wind directions. Moreover, it is shown that the drags and torques can be significantly reduced for columns with shrinking cross-sections with altitude. In summary, the effects induced by the twisting aloft wind due to the Coriolis force should be taken into account for high-altitude structures inside the atmospheric boundary layer. Column with shrinking cross-sections provide an alternative design for high altitude structures with smaller along/cross-wind drags and base torques.