Abstract
This paper presents the results of an experimental study on starting square jets at three Reynolds numbers (R_e=2358, 3528, 4716) utilizing Planar Laser Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV). Vortex leapfrogging and coalescence were found to appear at the lowest Reynolds number investigated while vortex pinch-off tended to appear at higher Reynolds numbers. The 'imperfect' leapfrogging between the third and the fourth vortex rings appears to promote growth of instability which leads to the transition to turbulence. The maximum circulation that a vortex ring can attain during its formation is reached at the non-dimensional time (t*=tW_0/D_e) within the range of 1.0〜2.33 which is lower than the universal time scale obtained by Gharib et al. for the circular jets with uniform initial velocity distribution. Axis switching was found to play an important role for the vortex development in square jets.
