半圓頂大跨度屋蓋結構在平滑流場及大氣邊界層流場中之風載重特性

characteristic of wind load on a hemispherical dome in smooth flow and tubulent boundary layer flow

傅仲麟(Chung-Lin Fu)

指導教授 ： 鄭啟明

淡江大學/工學院/土木工程學系博士班/博士(2010年)

https://doi.org/10.6846/TKU.2010.00564

摘要

近年來對於容納數萬人的體育場館或儲存大量工業原料的儲存空間之建築需求越趨殷切，而在利用風洞試驗評估此大跨度曲面結構屋蓋之受風載重時，曲面造型之風壓分佈會隨雷諾數之變化，而有不同的分佈狀況。本文之主要研究會分為三個階段，第一階段是以可視化方式，初步瞭解半圓球曲面屋頂在不同雷諾數周邊流場特性。而第二階段，將針對半圓球曲面屋頂建築，在平滑流場及紊流邊界層流場條件下進行較完整雷諾數範圍（約為7×104∼2×106）之風洞試驗，並針對風壓分佈及風壓特性之深入探討。第三階段將針對不同雷諾數及不同紊流條件下之風壓分佈及風載重特性進行試驗及討論。
研究結果顯示，在平滑流場條件下，在雷諾數小於2.0×105時，氣流接觸半球體後，在半球體表面形成層流邊界層，而後約於85度與半球體分離。當雷諾數大於3.0×105時，因邊界層由層流轉變為紊流，分離點往下游延伸，並且形成separation bubble，因此使得流體分離後的區域大幅縮減，因而使得在臨界雷諾數處阻力大幅下降。
在紊流邊界層的流場條件下，紊流邊界層流場之臨界雷諾數會低於平滑流場之臨界雷諾數。因此在雷諾數大於1.8×105時，流場開始保持較穩定狀態。因此，壓力分佈及風力係數皆達到穩定狀態。而與平滑流場比較，紊流邊界層流場條件下，除了在分離點附近會有較大之擾動風壓外，約20度處受邊界層大尺度紊流影響，亦會產生較大的擾動風壓。
此外，當大跨度建築所在流場整體紊流強度大於15％時，即使雷諾數低於2.0×105，建築物所受風壓特性亦不受雷諾數之影響。但若雷諾數大於3.0×105，則即使紊流強度偏低，則建築物所受風壓特性亦可維持穩定不再隨雷諾數變化而變動，但不同紊流強度其風壓特性會有所不同。由POD模態分析結果可知，在紊流強度較大的流場條件下，其擾動能量較集中於前幾個模態，而紊流強度較低的流場條件下，擾動能量較分散於各個模態上。此外，紊流強度除影響能量分佈外，亦會影響模態分佈形狀。

關鍵字

大跨度 ； 半球體 ； 風洞實驗 ； 雷諾數

並列摘要

Due to the structural efficiency and economic benefit, the hemispherical dome is a common structural geometry shape for large span sports stadiums or for storage purposes. The curved shape makes the accurate estimation of the wind pressure fluctuations on a hemispherical dome a difficult task due to the Reynolds number effects.
A series of wind tunnel tests were performed to investigate the effects of Reynolds number on the aerodynamic characteristics of hemispherical dome in smooth and turbulent boundary layer flows. Reynolds number of this study varies from 5.3 × 104 to 2.0 × 106. Instantaneous pressures were measured through high frequency electronic scanner system. Mean and RMS pressure coefficients on the center meridian and the overall pressure patterns of domes were calculated for comparative study. The results indicate that, In the smooth flow, the transition phenomenon of separated free shear layer occurs near Re=1.8×105 ~ 3.0×105；The separation/reattachment occurs in this Reynolds number region. The mean and R.M.S. pressure distributions become relatively stable after Re>3.0×105. The mean meridian drag coefficient decreases with Reynolds number for Re<3.0×105, and then increase monotonically up to Re=2.0×106; RMS meridian drag coefficient shows maximum and minimum values at Re≒1.5×105 and 3.0×105, respectively. The correlation coefficients of mean and RMS pressure contours indicate that, the pressure distributions become relatively stable at Re=2.0~3.0×105.
In turbulent flow, the transition phenomenon of separated free shear layer occurs at a lower Reynolds number, Re<1.1×105, and both mean and RMS pressure distributions approach Reynolds number independent when Re=1.2~1.5×105. The mean and RMS meridian drag coefficients, Cd and Cd’, become invariant when Re>2×105. The correlation coefficients of mean and RMS pressure contours indicate that, in turbulent boundary layer flow, the pressure distributions become Reynolds number independent at Re=1.0~2.0×105.
The Proper Orthogonal Decomposition (POD) was then applied to the pressure measurements of the uniformly distributed dome to study the wind load patterns of the hemisphere dome in both smooth and turbulent boundary layer flows. For a hemisphere dome submerges in a turbulent flow, the fluctuating energy concentrated the few POD mode. For the dome in smooth flow, however, the fluctuating energy is spread over large number of POD modes.

並列關鍵字

long span ； Hemisphere ； wind tunnel test ； Reynolds number

參考文獻

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