Particle image velocimetry (PIV) was employed to measure the flow field quantitatively at the transitional Reynolds number to investigate the large scale structure in channel flow at transitional state. The intermittent instantaneous velocity field was captured, and the large-scale structure in stripe shape was extracted from the flow field reconstructed on the basis of the Taylor's hypothesis. The results show that there is an angle of about 25°30° between the borderline of the high velocity stripe and the low velocity stripe and the flow direction. The absolute values of the skewness factor and the flatness factor decrease with the decrease in Reynolds number, indicating that the turbulent events become fewer and the flow state tends to be laminar. In addition, the flow state changes dramatically at Reynolds number from 1 300 to 1 600 according to the flow field and the high-order statistics.%为了研究槽道湍流与层流过渡流态下流场中的大尺度流动结构,采用粒子图像测速仪对过渡雷诺数下平板槽道内的流场进行了定量测量,捕捉到了高速区域与低速区域相间的瞬时流场,并基于Taylor假设对所测流场进行了重构,从多个瞬时流场中提取出大尺度条纹状结构.结果表明:这种条纹结构与流动方向之间存在一定的夹角,大约为25°～30°；倾斜因子和平坦因子的绝对值随雷诺数的减小而减小,即湍流猝发事件减少,间歇性减弱,流动趋于有序,逐渐向层流转化.从流场及统计量的变化还可以看出:当1 300≤Rem≤1 600时,流场的变化最显著.
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