可變溫度及紊流風洞之流場量測研究

Abstract

中文摘要 本研究主要以實驗的方式探討可供控制且相當均勻的高溫及低溫紊流流場，其中流場溫度範圍為300~900K，流場平均速度範圍為0.5~2m/s，流場紊流強度範圍為1.5~24.7%，流場特徵完整尺寸尺度(integral length scale)範圍為1.3~10.8 mm，格摩拉夫微小長度尺寸(Kolmogorov microscale)範圍為0.18~2.8 mm，來提供往後液滴蒸發實驗之所需流場，並再深入瞭解流場中特徵尺寸尺度彼此間相互影響的關係。在實驗方法上，乃是採用雷射都卜勒測速儀(LDA)來量測流場的基本性質，找出紊流場中具均質性(homogeneous)的區域範圍，以決定液滴實驗中液滴的測試位置。 本實驗主要探討吾人所設計之風洞的特性，其中包括常溫及高溫圓管流紊流場及高紊流流場的平均速度分佈剖面、速度擾動分佈剖面、能量頻譜分析、速度擾動之概率密度函數分析( PDF，Probability Density Function )做一個全面性的探討，本文採用Hinze (1975)的理論，找出流場中的各種特徵尺度與時間尺度。

ABSTRACT An open-air vertical, circular wind tunnel has been constructed to generate the nearly uniform high- and low- turbulence flow field at various temperatures, which is capable of producing free stream with mean velocities of 0.5~2m/s, turbulence intensities of 1.5~24.7%, and temperature of 300~900K. Turbulence environments are controlled by the different sizes of the turbulent generating disk. Laser Doppler Velocimeter is used to characterize the turbulence properties of the wind tunnel, including the mean streamwise velocity, turbulent intensity, probability density function and energy power spectrum. Integral length scale and Komogorov microscale are computed using Taylor hypothesis and assuming isotropic turbulence theory, respectively. A relatively homogeneous region about 20 mm in the middle of the tunnel exit is identified, which is wide enough for future droplet experiments.