PIV study on intermittent flow structure in poiseuille channel flow at transitional reynolds number

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.