以RANS紊流模式計算導流結構對高樓建築風阻減降效果之研究

Investigation of drag reduction for high-rise building by introducing flow guided structures with using the RANS model

許博智(Po-Chih Hsu)

指導教授 ： 朱錦洲

共同指導教授 ： 張建成(Chien-Cheng Chang)

國立臺灣大學/工學院/應用力學研究所/碩士(2022年)

https://doi.org/10.6342/NTU202203013

摘要

本論文是以數值模擬方法利用導流結構對實際尺度之高樓風場進行減阻效果之研究，高樓模型為樓高H=80公尺，高寬比AR=5之立方柱，並在其上游擺放有1/5高樓寬之立方柱作為導流結構。考慮大氣邊界層效應並以半經驗指數律速度剖面作為流場入流條件。在取樓高為特徵長度，並以地面至樓頂高度之入流平均速度作為特徵速度條件下，流場之雷諾數為7.67×10^7。數值模擬使用Fluent Meshing建立數量在940萬至980萬間不等之Poly-Hexcore網格。在邊界層內以15層邊界層網格進行網格設置，並將第一層網格高度限制在對數律層內；在邊界層網格處理上使用增強型壁面函數對壁面進行近壁處理。由於本流場屬於高雷諾數紊流流場且存在分離流動，因此紊流模式使用基於雷諾平均理論的SST k-ω模式進行CFD模擬。
本研究是以導流結構高度h與高樓與導流結構之間的距離S，作為操縱變因，探討高樓上游之導流結構在改變下游流場後對目標高樓風阻減降之效果。研究之導流結構高度共設置有0.5H、0.6H、0.7H、0.8H、0.9H、1.0H六組高度。而高樓與導流結構之間的距離則由起始的0.5D開始，以0.5D作為固定間隔逐漸增加距離至5D為止。研究結果顯示導流結構高度與減阻效果整體趨勢呈現正相關，在h=0.5H之導流結構條件下，高樓的減阻效果最高僅有9.7%；而h=1H之導流結構最高則有66.7%減組效果。在改變間隔距離研究結果方面，在特定間隔距離下會對高樓產生最佳減阻效果，0.9H及1H導流結構高度在S=1.5D、3.0D間隔時有最佳及次佳的減組效果，而0.5H、0.6H、0.7H導流結構高度條件下在3.0D、3.5D間隔時會有最佳的減組效果。

關鍵字

計算流體力學 ； 計算風工程 ； 紊流模式 ； 雷諾平均方程式 ； 高樓減阻 ； 風場模擬 ； 高雷諾數

並列摘要

In the present study, a numerical simulation was carried out for investigating the effect of drag reduction of a full-size high-rise building in the turbulent wind field. The building is an 80-meter high rectangular column with aspect ratio of 5. A flow-guiding structure is placed in the upstream of the building and the dimension is 1/5 of building width of varying height.
The exponential semi-empirical velocity profile is used representing the atmosphere boundary layer(ABL) inflow condition. Mosaic Poly-Hexcore meshes are used for spatial discretization of the computational domain with number of cells ranging from 9.3 to 9.6 million. 15-layers prism cells underneath the unstructured meshes close to wall are generated for the boundary layer treatment, and the first grid point from the wall is set slightly larger than buffer layer height with maximum y+≈50. In purpose of resolving turbulent flow with flow separation region, the SST k-ω model is used with enhanced wall function for efficient calculation due to the large Reynolds number(~10^7 ).
In this study, the height of the flow-guiding structure and the distance between the building and the upstream structure are used as manipulation variables to investigate on the drag reduction effect. The symbol H、 D and S represent the height and the width of the building, and the distance between the building and the flow-guiding structure respectively. The height of the flow guiding structure is 0.5H、0.6H、0.7H、0.8H、0.9H 、1.0H and the distance S ranges from 0.5D to 5.0D with 0.5D fixed intervals.
The results imply that the presence of the taller flow-guiding structure results in lower drag coefficient, having better effect of drag reduction percentage. The maximum drag reduction percentage is 66.7% in the case of 1.0H. Much higher than that of merely 9.7% when the flow-guiding structure is half the building height.
In the case of 1.0H and 0.9H, the highest and second highest drag reduction percentage happened at S=1.5D and 3.0D respectively. On the other hand, when the height of the flow-guiding structure are 0.8H、0.7H and 0.6H, the highest drag reduction percentage happened in farther distance, that is 3.0D and 3.5D.

並列關鍵字

computational fluid dynamics ； computational wind engineering ； turbulent models ； RANS ； high-rise building ； drag reduction ； wind loads simulation ； high Reynolds number

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