渦輪機葉片冷卻內流道熱傳研究

A Study of Heat Transfer for Internal Cooling Passage of Gas Turbine Blades

李信龍(Hsin-Lung Li)

指導教授 ： 蔣小偉

國立清華大學/工學院/動力機械工程學系/博士(2014年)

摘要

由理想布萊登循環可知，若提高渦輪機進口之燃氣溫度，則系統整體之熱效率也將獲得大幅之提升，在目前的渦輪機葉片內部冷卻方式中，大多以內冷卻流道配合衝擊冷卻方法，以降低渦輪機葉片之溫度；除了高溫的邊界條件外，由於渦輪機葉片在實際操作過程中，處在高速的旋轉情況下，因此為了較真實的探討其內部管道之熱傳現像，研究過程中須同時考慮科氏力之效應。
本研究中以實驗方式探討在測試段旋轉下，柯氏力效應對於流道內部強制對流冷卻及衝擊冷卻熱傳效果之影響，流道之幾何特徵為均勻方形截面(10mm×10mm)且不具肋條之平滑表面，壁面加熱條件為固定熱通量；研究內容分為兩大部分，首先探討四通道蛇型流道於不同轉速及入口雷諾數下之壁面熱傳效果，接下來以具有單一噴流孔之直通道，探討其在不同噴流雷諾數及橫風雷諾數條件下，衝擊靶面受科氏力影響後之熱傳變化。
在實驗中顯示，不論是在靜止或旋轉下，提高入口雷諾數皆可增進流道壁面之熱傳效果，而相較於直流道之壁面，在蛇型流道之彎道處，明顯的有較佳之熱傳效果，且彎道內外側壁面呈現較大之熱傳差異，此外在旋轉下，柯氏力效應造成不同流道中，迎風面與背風面之熱傳差異，而隨著轉速增加流道壁面之平均熱傳效果也隨之提升，特別是在流道下游處。
而在衝擊冷卻實驗中整體而言，加熱靶面之平均熱傳效果隨著衝擊流雷諾數的增加而變好，但隨著轉速提高而變差，此意味著橫風雷諾數及轉速的增加將會使得衝擊流受到偏折，造成靶面之衝擊冷卻效果受到抑制，因此在低橫風雷諾數及低轉速下，衝擊流對於加熱靶面之平均熱傳效果有較大之增益，此現象在低衝擊流雷諾數下更為明顯。

關鍵字

渦輪機葉片 ； 蛇行冷卻流道 ； 科氏力 ； 離心力 ； 衝擊冷卻 ； 旋轉

並列摘要

By ideal Brandon cycle, the turbine’s inlet temperature will be raised up, as well as the whole heat efficiency of the system. So far, most cooling approach of turbine blades’ interior is using internal cooling passage collocated with impingement cooling approach. Because that turbine blade operate in high temperature and high rotational speed condition, the Coriolis force must be considered while discussing the heat transfer of internal passage.
This research discuss how Coriolis force affect the force convection cooling and impingement cooling inside the passage in rotating condition by experiment. The geometry of the passage is 10 mm x 10 mm square without ribs. The surface heating condition is uniform heat flux; the contents of this research divide into two parts, firstly, discuss the heat transfer effect of Serpentine Passage with three corners in different rotating speed and different inlet Reynolds’ number. Finally, consider Coriolis effect on Impinge surface and discuss the variation of heat transfer effect inside the straight passage with single jet hole in different Reynolds’ number of Impingement Flow and cross flow.
By experiment, it reveals that whether it rotates or not, increase inlet Reynolds’ number can raise up the heat transfer effect on passage surface. The corner of Serpentine Passage has better heat transfer effect than straight passage, and it has more heat transfer difference between inside and outside corner surface. In addition, while rotating, Coriolis effect cause heat transfer difference between the surface against the wind and the leeward surface in different flow channels, and due to the increase of rotational speed, the average heat transfer effect also raise up, especially at the downstream of the flow channel.
In sum, in the Impingement cooling experiment, the average heat transfer on Heated Target Surface will be better with the increase of the Reynolds’ number of Impingement Flow but will be worse with the increase of rotational speed. It reveals that the Reynolds’ number of cross flow and the increase of rotational speed will make the Impingement Flow slant, restraining the Impingement cooling effect. As a result, In the condition of low Reynolds’ number of cross flow and low rotational speed, cross flow can cause much more increase of average heat transfer on Heated Target Surface, this phenomenon is more obvious in low Reynolds’ number of Impingement Flow.

並列關鍵字

Turbine Blade ； Serpentine Cooling Passage ； Coriolis force ； Centrifugal Force ； Impingement Cooling ； Rotation

參考文獻

1. Kim Kyung Min, Kim Yun Young, Rhee Dong Ho, and Cho Hyung Hee,2004, “An Investigation Of Duct Aspect Ratio Effects On Heat/Mass Transfer In A Rotating Duct With 90-Degree Ribs, ”ASME IGTI. GT2004-53533.

2. Cho Hyung Hee, Kim Yun Young, Kim Kyung Min, Rhee Dong Ho,2003, “Effects Of Rib Arrangements And Rotation Speed On Heet Transfer In A Two Pass Duct , ”ASME IGTI. GT2003-38609.

3. Kuo, C. R., and Hwang, G. J., 1993, “Experimental Study of Convective Heat Transfer in a Radially Rotating Square Duct with Uniform Wall Heat Flux and Inward Flow,” 93-WA/HT-54, presented at the ASME Winter Annual Meeting, New Orleans, Lousiana, Nov. 28-Dec. 3

4. Kuo, C. R., Chen, J. L., and Hwang, G. J., 1993, “Experimental Study of Convective Heat Transfer in a Radially Rotation Square Duct with Uniform Wall Heat Flux and Inward Flow, 93-WA/HT-54,” presented at the ASME Winter Annual Meeting, New Orleans, Lousiana, Nov. 28-Dec.3.

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