超音速高溫衝擊流之暫態分析

NCU Institutional Repository > 工學院 > 機械工程研究所 > 博碩士論文 > Item 987654321/2577

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题名:	超音速高溫衝擊流之暫態分析
作者:	邱清楓;Ching-feng Chiu
贡献者:	機械工程研究所
关键词:	高溫衝擊流;超音速衝擊流;熱輻射;離散座標法;impinging jet;radiation;supersonic jet;transient flow
日期:	2005-06-28
上传时间:	2009-09-21 11:50:56 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	本論文是應用數值方法，在考慮輻射效應下，探討超音速高溫衝擊流熱流特性隨時間的變化情形。整個幾何模型由於軸對稱，簡化成二維模型。紊流模式採用k-?模型。輻射熱傳利用離散座標法求解，包含吸收與放射效應。數值計算主要分為二個部分，第一部分為固定噴嘴位置，改變噴嘴出口條件和衝擊距離，第二部分為噴嘴隨時間向上移動，改變噴嘴出口條件。固定噴嘴位置時，噴流在離開噴嘴後，即開始向下擴張，馬赫盤逐漸靠近地面，在環流區要產生之前才回升至一固定高度，馬赫盤內為一高溫區，在時間為0.001秒時，噴流受到各震波間相互影響而產生一股強力迴流，將高溫區內的能量往外帶，產生一大範圍的次高溫區，直到環流區形成時，迴流消失，次高溫區內的能量隨著噴流由軸向轉為徑向帶走而跟著消失。增加噴嘴出口溫度時，馬赫盤越快靠近地面而回升，環流區越早形成。當衝擊距離增加到四倍噴嘴直徑(Z/D=4)時，無環流區產生，再增加到Z/D=6時，會有一較小範圍的環流區產生。對所探討之參數範圍，在時間0.01秒後流場與溫度場之特性已趨於穩定。移動噴嘴時，環流區形成之後，噴嘴繼續向上移動，馬赫盤隨之上升，整個環流區向上拉長，直到噴嘴到達Z/D=4時，環流區消失，流場結構轉為無環流結構，當噴嘴持續上升到Z/D=6時，才又產生環流區。噴嘴出口速度和壓力越大時，馬赫盤上升導致環流區被向上拉長的趨勢越明顯，增加噴嘴出口壓力，流場不會先變成無環流結構的狀態之後，再產生環流區，而是一直保持著有環流結構的狀態。在時間為0.01秒之後，噴嘴已遠離衝擊面，流場和溫度場之特性趨於穩定。 The transient flow and thermal characterisitcs of a hot supersonic impinging jet with radiation effects are studied. Two dimensional, cylindrical, unsteady supersonic impinging jet is simulated using the STAR-CD. Turbulent flow is simulated using the κ-ε model. The equation of radiative transfer is solved by the discrete-ordinate method. Results are obtained for two cases. Case one is for fixed nozzle position while case two is for moving nozzle. The effects of various parameters, such as nozzle exit temperature, pressure, velocity and the distance between the nozzle and the impingement surface are studied. For fixed nozzle case, the results show that as the jet leaves the nozzle, it expands down quickly. Before the circulation bubble come to existence, the Mach disk moves towards the impingement surface gradually. At the time of 0.001 second, the jet has a strong recirculation near the end of the oblique shock, creating a large-scale second high temperature field. Increasing the nozzle exit temperature causes the bubble to form earlier. The flow reaches steady state at 0.01 second approximately. For the moving nozzle case, the results show that after the circulation bubble come to existence, the Mach disk moves upwards with the moving nozzle, and hence the circulation bubble is also pulled upward. As the nozzle reaches the position where the distance between the nozzle and the impingement surface is 4 times the nozzle diameter (Z/D=4), the circulation bubble vanishes. The bubble will form again at Z/D=6, but become smaller in size. Increasing the nozzle exit pressure or velocity causes the phenomenon of the circulation bubble be pulled upward more obviously. The circulation bubble does not vanish at Z/D=4 for higher relative pressure (PR=3.4) case. After 0.01 second, the nozzle is far from the impingement surface, the flow is not affected by the pressure of the impingement plate.
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