The Effects of a Backward-Facing Entrance Step on Heat Transfer and Film Cooling in the Endwall Region of a Vane
邱耀俊、吳佩學
E-mail: 9419540@mail.dyu.edu.tw
ABSTRACT
This article is concerned with a practical problem regarding external heat transfer at the endwall of a vane in a gas turbine. A downward step in the flow direction normally occurs at the exit of the combustion gas duct which connects the combustion chamber and the first stage guide vanes. For a flow passage in between any two adjacent vanes, this is a backward-facing entrance step. Due to thermal expansion of different materials, the size of the step, and thus the downstream thermal and flow fields, may also change with the load of the gas turbine. Based on the smooth endwall condition, the effects of the entrance step on heat transfer coefficient and film cooling effectiveness of the endwall inside the vane passage are investigated in this study. A two-half vane with side bleeding gaps is used as the test model. The downward step size, S, is taken as 4% of the chord length. Film coolant injects into the main flow at an angle of 45 degrees with the endwall. All the film cooling holes do not include any compound angle. The main flow Reynolds number is kept at Rec = while the blowing rate of the film coolant is either 0.5 or 2.0. Experimental results using thermochromic liquid crystal technique show that a backward-facing entrance step causes a remarkable increase in the heat transfer coefficient at the endwall. Although most of the endwall surface has higher film cooling effectiveness for the case with a downward step, it does not help much to eliminate the hot spot near the flow reattachment point. Keywords： downward step, endwall, film cooling, heat transfer coefficient
Keywords : Backward ; Vane ; Film
Table of Contents
封面內頁 簽名頁 授權書 iii 中文摘要 iv 英文摘要 v 誌謝 vii 目錄 viii 圖目錄 x 表目錄 xiv 符號說明 xv 第一章 問題描述 1 1.1 前言 1 1.2 研究動機 2 1.3 研究之目的 4 第二章 國內外之研究情形 5 2.1 端壁區域熱傳與膜冷卻 5 2.2 端壁區域三維流場 13 第三章 研究方法與進行步驟 17 3.1 測試段 17 3.1.1 雙半葉片模型與底板設計 17 3.1.2 進口台階設計 18 3.1.3 間隙大小模擬 18 3.2 熱傳實驗系統 19 3.2.1 熱線風速儀校正 19 3.2.2 溫度量測校正 21 3.2.3 風洞品質鑑定 22 3.2.4 紊流強度場 23 3.2.5 液 晶校正 23 3.2.6 暫態熱傳液晶實驗條件 24 3.2.7 穩態液晶實驗條件 24 3.2.8 暫態熱傳液晶實驗架構 24 3.2.9 穩態液晶實驗架 構 25 3.2.10 暫態液晶實驗影像處理系統 25 3.2.11 穩態液晶實驗影像處理系統 25 3.2.12 暫態液晶實驗數據化約流程 26 3.2.13 穩態液晶實驗數據化約流程 26 3.3 基本理論 26 第四章 結果與討論 34 4.1 端壁熱傳係數結果 34 4.2 端壁膜冷卻有效 性結果 35 第五章 結論 39 參考文獻 41
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