本研究分別使用質點影像測速儀(Particle Image Velocimetry)與紅外線測溫儀(Infrared Thermography)量測一渦輪機葉片中180度銳轉平滑壁面正方形冷卻雙通道的紊流場結構與壁溫分布。雷諾數(Reynolds number)在量測紊流場結構時訂於5300；而在量測壁溫分布時，雷諾數則從5000變化至20000。除了平均速度(U_st, U_sp, and U_ver)與紊動速度(u_st, u_sp, and u_ver)之外，本研究將會探討轉彎效應對於紐賽數比(Nu⁄〖Nu〗_∞ )和高階紊流統計參數的影響，其中高階紊流統計參數包含雷諾剪應力((u_st u_sp ) ̅, and (u_sp u_ver ) ̅)、紊流動能(k)、歪斜度(S)、平坦度(F)、紊流時間與長度尺度(τ_st, τ_sp, τ_ver, and λ_ver)、紊流能量頻譜(E)、以及紊流動能產生項。
研究結果顯示在轉彎區到轉彎後一倍水力直徑之間，F會隨著S的上升而下降，反之亦然，此結果並未見於先前單通道的文獻。除此之外，透過一維的時間頻譜分析可以發現在轉彎區正中央的剪力層上有一260Hz的主頻(Predominant Frequency)。利用流場可視化可以發現此主頻與剪力層上渦旋的產生頻率相符合。而與此渦旋相關的τ_sp側向分布也被進一步的發現與轉彎區的Nu⁄〖Nu〗_∞ 側向分布有著高度相關性。
透過相關係數(Pearson Product-Moment Correlation)的計算，本研究可以定量的分析出與Nu⁄〖Nu〗_∞ 有著高度、中度、和低度相關性的流力參數，分別為平均渦度大小((|ω| ) ̅)、(√((〖U_st〗^2+〖U_sp〗^2)), u_sp, u_ver, k, (u_sp u_ver ) ̅, τ_sp, and τ_ver)、和(U_ver, u_st, (u_st u_sp ) ̅, S, F, τ_st, λ_ver)。根據以上結果，本研究首先提出一描述本180度銳轉平滑壁面正方形雙通道中(|ω| ) ̅和Nu⁄〖Nu〗_∞ 之關係的經驗公式。

Turbulent flow structures and heat transfer in a 180-deg sharp turning two-pass internal coolant passage of a turbine blade are investigated experimentally by particle image velocimetry (PIV) and infrared thermography (IRT) techniques. The coolant passage has a square cross-section and smooth wall. The Reynolds number (〖Re〗_b) based on bulk mean velocity (U_b) and duct hydraulic diameter (D_H) for PIV and IRT measurements are respectively 5300 and 5000-20000. In addition to the mean velocity (U_st, U_sp, and U_ver) and fluctuating velocity (u_st, u_sp, and u_ver), the turn effects on the Nusselt number ratio (Nu⁄〖Nu〗_∞ ) and spanwise distributions of high-order turbulence statistics including Reynolds shear stresses ((u_st u_sp ) ̅, and (u_sp u_ver ) ̅), turbulent kinetic energy (k), skewness factor (S), flatness factor (F), integral scale (τ_st, τ_sp, τ_ver, and λ_ver), energy spectrum (E), and production term of turbulent kinetic energy are explored in the present study.
The results show that F in between the pre-turn and post-turn 1D_H decreases with increasing S and vice versa, which has not been previously reported for single-pass duct flow. Meanwhile, from both 1-D longitudinal and spanwise temporal spectra, a predominant frequency of 260Hz is spotted at the divider tip shear layer and qualitatively verified by flow visualization. As a relevant parameter of shedding vortex, the spanwise profiles of τ_sp are further found to be in strong correlation with the spanwise Nu⁄〖Nu〗_∞ distributions.
Using Pearson product-moment correlation, the present study is capable of quantitatively identifying the highly, moderately, and weakly correlated fluid flow parameters on Nu⁄〖Nu〗_∞ as mean vorticity magnitude ((|ω| ) ̅), (√((〖U_st〗^2+〖U_sp〗^2)), u_sp, u_ver, k, (u_sp u_ver ) ̅, τ_sp, and τ_ver), and (U_ver, u_st, (u_st u_sp ) ̅, S, F, τ_st, λ_ver), respectively. Based on these parameters, an empirical correlation formula between (|ω| ) ̅ and Nu⁄〖Nu〗_∞ in the present two-pass smooth square duct with 180-deg sharp turn is proposed for the first time.

List of Tables iv
List of Figures v
List of Symbols xii
Chapter 1 Introduction 1
1-1 Preliminary Remark 1
1-2 Literature Survey 2
1-2-1 Flow Field for Fully Developed Single Pass Channel/Pipe 2
1-2-2 Flow Field for Curved Channel/Pipe 6
1-2-3 Flow Field for U-Bend 8
1-2-4 Flow Field for 180-Deg Sharp Turning Duct 12
1-2-5 Heat Transfer in 180-Deg Sharp Turning Smooth Square Duct 15
1-2-6 Relation between Fluid Flow Parameters and Heat Transfer in 180-Deg Sharp Turning Smooth Square Duct 17
1-3 Objectives 19
Chapter 2 Experimental Apparatus and Conditions 31
2-1 Experimental Apparatus in Flow Field Measurement 31
2-1-1 Particle Seeding System 31
2-1-2 Laser System 33
2-1-3 Image Capture System 33
2-1-4 Data Processing System 34
2-2 Experimental Apparatus in Heat Transfer Measurement 35
2-2-1 Infrared Camera System 35
2-2-2 Thermocouple System 36
2-3 Test Model 36
2-3-1 Test Model for PIV Measurement 36
2-3-2 Test Model for IRT Measurement 37
2-4 Experimental Conditions 38
Chapter 3 Data Processing and Uncertainty Analysis 51
3-1 Mean Flow and Turbulence Statistics 51
3-2 Nusselt Number 53
3-3 Correlations between Heat Transfer and Flow Field Parameters 55
3-4 Uncertainty Analysis 57
3-4-1 Uncertainty Analysis for Flow Field Measurement 57
3-4-2 Uncertainty Analysis for Heat Transfer Measurement 58
Chapter 4 Results and Discussion 65
4-1 Fully Developed Flow in Smooth Square Duct 65
4-1-1 Streamwise Mean Velocity 65
4-1-2 Fluctuating Velocity and Reynolds Stress 67
4-1-3 Skewness Factor and Flatness Factor 68
4-1-4 Two-Point Correlation (Spatial Correlation) 69
4-1-5 Autocorrelation (Temporal Correlation) 71
4-1-6 One-Dimensional Wavenumber Spectra 72
4-1-7 Frequency Spectra 74
4-1-8 Energy Budget of Turbulent Kinetic Energy 75
4-2 Mean Flow Structure in 180-Deg Sharp Turning Smooth Square Duct 76
4-2-1 Evolution of Mean Velocity 76
4-2-2 Cross-Section Secondary Flow Patterns 78
4-3 Mean Velocity and Turbulence Statistics on Y* = 0 Plane 79
4-3-1 Mean Velocity 80
4-3-2 Fluctuating Velocity 82
4-3-3 Reynolds Shear Stress 85
4-3-4 Skewness Factor 86
4-3-5 Flatness Factor 89
4-3-6 Temporal Integral Scale 91
4-3-7 Frequency Spectrum 93
4-3-8 Production Term of Energy Budget 96
4-4 Heat Transfer Measurement Results 98
4-4-1 Heat Transfer Features in a 180-Deg Sharp Turning Smooth Square Duct 99
4-4-2 Evolution of Heat Transfer Enhancement before and after the Turn 100
4-4-3 Relations between Heat Transfer and Near-Wall Turbulence Statistics 101
4-5 Quantitative Analysis of Heat Transfer and Flow Field 105
4-5-1 Correlation between Nusselt Number and Turbulence Statistics 105
4-5-2 Regression Analysis between Nusselt Number and Vorticity 110
Chapter 5 Conclusions and Recommendations 178
5-1 Conclusions 178
5-2 Contributions 182
5-3 Future Recommendations 183
Appendix A Development of Turbulent Duct Flow 185
Appendix B Dimensional Analysis of Vorticity 189
References 192

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