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研究生:陳世明
研究生(外文):Shi-Ming Chen
論文名稱:風驅動水面下紊流邊界層流場與其分子次層之流場結構
論文名稱(外文):The Flow Structures Within the Turbulent Boundary Layer and the Molecular Sublayer Beneath a Wind-Driven Water Surface
指導教授:蔡武廷
指導教授(外文):Wu-Ting Tsai
學位類別:碩士
校院名稱:國立交通大學
系所名稱:土木工程系
學門:工程學門
學類:土木工程學類
論文種類:學術論文
論文出版年:2003
畢業學年度:91
語文別:中文
中文關鍵詞:邊界層分子次層
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本研究分析數值模擬風趨動水面下紊流邊界層之三維流場資料,以驗證氣-水傳輸「界面更新模式」中更新渦漩之存在,並進而探討更新過程之流場結構。論文首先推導以界面更新模式為基礎之分子次層流場平均分佈(包括速度、溫度與氣體濃度),此理論分佈呈現指數函數形態,異於傳統無滑移牆面邊界分子次層流場之線性分佈。數值模擬與實驗量測結果之比較亦呈現此指數函數分佈形態,故間接驗證界面更新過程之存在。論文之第二部分為數值模擬流場之視覺化,以探討更新過程之流場結構。比較數值模擬與實驗觀測之水面流場,兩者呈現相同之水面特徵流場結構: 高速、低溫之沿流向條痕,以及阻擋條痕並使其分歧之低速、高溫水面發散局部區域。視覺化水面下三維流場發現,水面上發散區域乃自水下混合紊流湧升至水面之低速、高溫水流所造成。自水下三維流場之觀察,我們成功描述更新過程之流場結構,並進而解釋形成此流場之更新渦漩的產生與演化。然而對於分子次層內高速且低溫之沿流向條痕的生成,本研究僅討論其與冷表面效應之關聯性,其生成的動力機制仍有待進一步研究。

The three-dimensional field data from direct numerical simulations of the turbulent boundary layer beneath a wind-driven water surface is analyzed to validate the surface renewal model in air-water flux parameterization. The emphasis is on visualizing the surface renewal eddies as well as on elucidating the flow tructures associated with the renewal process. In the first part of the thesis, we reappraise the theoretical mean field distributions within the molecular sublayer, which is derived based on the conceptual surface renewal model. Both the theoretical distributions and the numerical results reveal that the mean velocity, temperature and gas concentration all exhibit exponential distributions across the sublayers beneath an air-water interface, which are different from the traditional linear profiles next to a no-slip wall boundary. By fitting the numerical data to the exponential profiles, and also by comparing the results with the experiment measurements, we validate indirectly the existence of the surface renewal
process. We then further investigate the transport process through two- and three-dimensional visualizations of the simulated field data. Cross examinations of the two- and three-dimensional flow visualizations reveal two major characteristic structures associated with the renewal process:
the streamwise-elongated, high-speed, cool streaks within the sublayer, and the intermittent, low-speed, warm upwellings arising from the mixed turbulent regime. From the observations
of these two coherent flow structures, we depict the formation and evolution of the renewal eddies in the transport process. We also discuss the correlation between the cold streaks within the thermal sublayer and the well-known cool skin effect.

一、前言
1.1 海洋與大氣的垂直交換過程
1.2 界面更新模式
1.3 水面下邊界層流場的實驗觀測
1.4 數值模擬數據之產生
1.5 論文架構
二、紊流邊界層之平均流場分佈
2.1 分子次層之熱量、動量與氣體之傳輸
2.2 以更新模式推導分子次層平均分佈函數
2.3 對數層平均分佈函數
2.4 分子次層指數分佈函數與對數層對數函數之交會
2.5 數值模擬與理論平均分佈之比較
三、三維流場結構與更新過程
3.1 水面特徵結構
3.2 三維流場結構
3.3 流場結構與更新過程之關係
四、結論與討論

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