中文摘要：

利用平面激光诱导荧光技术（PLIF）结合数字图像处理对不同 Re下液膜厚度的实时变化进行测量。通过MATLAB内建功率谱密度计算函数对液膜波动的时间序列进行进一步的处理，获得了液膜波动特性的功率谱密度（PSD）曲线，对不同 Re下的液膜波动规律进行了频谱分析。结果表明：液膜波动具有显著的多频特性，且各频率有优劣之分，孤立波数量虽少，却携带液膜波动的大部分能量，对液膜波动的贡献不可忽略。液膜波动幅度与 Re有关并呈现出一定的规律性：小 Re时，液膜的波动幅度与Re有强烈的相关性，随 Re的增大而增大；中等 Re时，液膜的波动幅度基本保持稳定；大 Re时，孤立波的出现使液膜波动幅度急剧增大，液膜波动不稳定性增强。

英文摘要：

A method of planar laser induced fluorescence （PLIF ） technology combined with digital image processing technology was proposed to measure the free falling film thickness on a vertical testing section .T he time sequences of film thickness of the film flow at different Reynolds numbers were obtained in the experiment . The frequency structure was analyzed on the base of the function which was used to calculate the power spectrum density in MATLAB .The results indicate that the thin‐film wave flow has the multiple frequency characteristics .The solitary‐type waves contain the largest portion of moving liquid mass .The wave amplitude depends strongly on the Reynolds number . The wave amplitude increases with the Reynolds number at small Reynolds number . The amplitude remains stable at medium Reynolds number .The appearance of the soli‐tary‐type waves at high Reynolds number leads to sharp increase of the wave amplitude and enhancement of the w ave instability .