衝擊距離對平板受振盪噴流衝擊之流場與熱傳特性的影響

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研究生：	彭韋綸 Wei-Lun Peng
論文名稱：	衝擊距離對平板受振盪噴流衝擊之流場與熱傳特性的影響 Effects of Impinging Distance of a Pulsating Jet on Flow and Heat Transfer Properties
指導教授：	黃榮芳 Rong-Fung Huang 許清閔 Ching-Min Hsu
口試委員:	黃榮芳 Rong-Fung Huang 許清閔 Ching-Min Hsu
學位類別：	碩士 Master
系所名稱：	工程學院 - 機械工程系 Department of Mechanical Engineering
論文出版年：	2016
畢業學年度：	104
語文別：	中文
論文頁數：	294
中文關鍵詞：	振盪噴流、衝擊距離、噴流衝擊熱傳
外文關鍵詞：	pulsating jet, impinging distance, jet impingement heat teansfer
相關次數：	點閱：258 下載：0
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上一筆

本研究使用振盪噴流衝擊一平板，以實驗方法探討衝擊距離、激擾史卓數及擾動強度對平板與噴流之間的流場特徵行為、壓力分佈與熱傳特性的影響。藉由調整揚聲器的頻率及電壓，控制振盪噴流的激擾史卓數與擾動強度。透過煙霧流場可視化技術的觀察，在激擾史卓數與擾動強度的域面上，流場行為可劃分為凝序性渦旋結構(coherent vortices)與具渦旋列之渦旋結構(vortex train)兩種特徵模態。藉由熱線風速儀量測噴流出口速度振盪及剪流層速度特性，分析時序圖及相對應的頻譜圖，並且根據流場可視化影像及熱線風速儀速度訊號，計算渦旋結構的群體移動速度。渦旋結構的群體移動速度隨著擾動強度與衝擊距離的提升而增加。利用壓力掃描器量測平板表面的壓力分佈，當衝擊距離減小與擾動強度增大時，在平板表面產生較大的壓力值。應用質點影像測速儀(PIV)量測全域速度場，量化流場結構、渦度場及紊流強度分佈。以紅外線熱顯像儀量測加熱平板的表面溫度分佈，比較自然對流、連續噴流及振盪噴流的紐塞爾數(Nusselt number)。具渦旋列之渦旋結構模態的紐塞爾數約為連續噴流的1.6至2.7倍，而凝序性渦旋結構模態的紐塞爾數約為連續噴流的1.2倍。因此，具振盪特性的衝擊噴流比連續噴流有較強的熱傳效果；振盪衝擊噴流在渦旋列模態時比凝序性模態有更顯著的熱傳效能。

The effects of impinging distance, excitation Strouhal number, and pulsation intensity on the instantaneous flow patterns, time-averaged velocity fields, pressure coefficients, and heat transfer characteristics of the pulsating jets impinging on a flat plate were experimentally investigated. According to the streak images of the laser-light sheet assisted smoke-flow visualization results, two characteristic flow modes, coherent vortices and vortex train, were identified in the domain of the excitation Strouhal number and pulsation intensity. The instantaneous velocities were measured simultaneously in the shear-layer near the jet exit and the flat plate by two hot-wire probes. The convection velocity of the vortical flow structure increases with increasing impinging distance and pulsation intensity. Surface pressure along a line on the flat plate across the center of the jet impinging area was measured by a pressure scanner. The results of pressure measurement showed that the averaged surface pressure increases with increasing pulsation intensity and decreasing impinging distance. The velocity field was quantified by employing the particle image velocimeter (PIV). The velocity vector field, streamline patterns, vorticity contours and turbulence intensity distribution were presented and discussed. The temperature distribution on the surface of the heated plate was measured by an infrared imaging system. The Nusselt numbers of the excited jet impingement are drastically larger than those of the unexcited jet. In the vortex train mode, the Nusselt numbers of the excited case are about 1.6 to 2.7 times of the unexcited case. In the coherent vortices regime, the Nusselt numbers of the excited case are about 1.2 times of the unexcited case.

摘要 ......................................................................................................i
Abstract ................................................................................................ii
誌謝 ....................................................................................................iii
目錄 ....................................................................................................iv
符號索引...........................................................................................vii
圖表索引............................................................................................ix
第一章 緒論 ......................................................................................1
1 研究動機 .....................................................................................1
2 文獻回顧 .....................................................................................1
2.1 振盪噴流 ..................................................................................1
2.2 壁面噴流 ..................................................................................3
3 研究目標 .....................................................................................5
第二章 實驗設備、儀器與方法 ...................................................7
1振盪噴流模型 .............................................................................7
2 實驗儀器與方法 ........................................................................7
2.1 連續噴流控制 .........................................................................7
2.2 噴流速度振盪量測 ................................................................8
2.3 煙霧流場可視化 .....................................................................9
2.4 質點影像速度儀 ...................................................................13
2.5 壓力量測 ................................................................................15
2.6 溫度量測 ................................................................................16
第三章 噴流的速度振盪特性 ......................................................17
1 噴流出口的速度特性 ..............................................................17
1.1速度振盪的時序訊號 ............................................................19
1.2 速度振盪的特性 ....................................................................25
1.3 時間差的特性 ........................................................................25
2 擾動強度與激擾電壓之關係 .................................................26
第四章 振盪噴流衝擊平板時的流場特徵與速度特性 ..........27
1 流場特徵 ....................................................................................27
1.1 H/d = 3的流場特徵 ................................................................28
1.2 H/d = 5的流場特徵 ................................................................34
1.3 H/d = 7的流場特徵 ................................................................39
1.4 衝擊距離與流場特徵之關係 ..............................................44
1.5 影像分析之群體速度 ...........................................................45
2 渦旋結構速度特性 ...................................................................46
2.1速度時序訊號 ..........................................................................46
2.2 速度訊號分析之群體速度 ...................................................58
第五章 平板表面壓力特性 ............................................................60
1 平板表面壓力分佈 ....................................................................60
2 平均壓力分佈 .............................................................................68
3 壓力係數 ......................................................................................73
第六章 振盪噴流衝擊平板時之速度場 ......................................75
1 速度流線 .....................................................................................75
2 渦度特性 .....................................................................................81
3 平均速度與紊流強度分佈特性 .............................................86
第七章 平板受振盪噴流衝擊時之熱傳特性 .............................97
1 自然對流的熱傳特性 ...............................................................98
2 連續噴流的對流熱傳特性 ......................................................99
3 振盪噴流的對流熱傳特性 ....................................................101
第八章 結論與建議 .......................................................................110
1 結論 ............................................................................................110
2 建議 ............................................................................................112
參考文獻  ...........................................................................................113

                                

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