波狀側壁矩形肋化雙道通暫態熱傳性能

Thermally Transient Heat Transfer Performance of Rectangular Twin-Pass Ribbed Channel with Skewed Wavy Sidewalls

本複合式熱傳強他裝置應用管壁斜肋及傾斜正弦波側壁於管道中所導引之同向渦流，提高熱傳增益效果，強化燃氣渦輪葉片內冷卻系統效能。本研究將此複合式熱傳強他裝置應用於寬高比為1之急彎雙流道，量測雷諾數（Re）為7500、10000、12500、15000、20000，其斜肋壁面之熱暫態傳熱性能。於任一測試雷諾數，測試管道之流體邊界層於熱邊界層發展前，已發展完成。於熱邊界層發展中階段，本研究採用每秒60張檢測面之高速紅外線熱像檢測技術，依時序量測於熱邊界層發展中之詳細斜肋壁面紐塞數（Nusselt number, Nu）分佈。藉由分析此暫態過程量測之熱傳係數分佈面、紐塞數分佈剖面及區域平均紐塞數，說明此測試件於熱暫態過程之熱傳性能，進而探討此測試管道於各測試雷諾數所需之穩態時間及相對應之紐塞數變化範圈。為評估此複合式熱傳強化裝置之熱傳增益效果，將穩態面積平均紐塞數（NU_A）與Dittus-Boelter紐塞數基準值（Nu_∞）比較，並推導出NU_A/Nu_∞之實驗公式，供相關工程領域應用。為彰顯此複合式熱傳強化裝置相應之壓損增益，將穩態條件量測之管道壓損係數（f），以Balssius壓損條數值（f_∞）標準化，並藉以評估此測試管道之熱性能係數。 A compound passive Heat Transfer Enhancement (HTE) method that utilizes the co-swirls tripped by the endwall angled ribs and the skewed sinusoidal sidewall waves is newly devised with cooling applications to gas turbine blades. Fitted with present HTE measure, the thermally transient heat transfer properties of a square twin-pass sharp-bend channel of AR (Aspect Ratio)=1 are detected at Reynolds number (Re) of 7500, 10000, 12500, 15000 and 20000. Prior to initiating the thermal boundary layer at each tested Re, the hydrodynamic boundary layer of the coolant flow is fully developed. A series of successive full-field endwall Nusselt number (Nu) distributions during which the thermal boundary layer is developing are detected using the infrared thermography technique at high rate of 60 FPS (Frame per Second). A set of full-field, sectioned and regionally averaged Nusselt number data is selected to illustrate the thermally transient heat transfer performances of present test channel. Transient periods for thermal boundary layer developments at all the tested Re are determined with the corresponding ranges of Nu variations evaluated. As an index to highlight the HTE benefit achieved by present HTE measure, the steady state area-averaged endwall Nusselt numbers (NU_A) is compared against the Dittus-Boelter Nu_∞, references with the NU_A/Nu_∞, correlation developed to assist relevant engineering applications. Pressure drop coefficients (f) measured at steady states are normalized by the Balssius equation levels (f_∞) to highlight the pressure drop penalties for acquiring the HTE benefits Thermal Performance Factors [TPF=( Nu_A /Nu_∞)/(f/f_∞)^(1/3)] evaluated.