ABSTRACT
Two distinct types of vortex dislocation generated in wake-type flows with different spanwise nonuniformities are numerically studied by direct numerical simulation (DNS). A local spanwise disturbance to the velocity of the oncoming flow leads to a generation of consecutive twisted vortex dislocations in the middle downstream, which is mainly caused by phase differences among vortex-shedding cells. A stepped variation of velocity in the oncoming flow yields a periodic vortex splitting-reconnection type of dislocation, which is mainly caused by frequency differences among the shedding cells. Dynamics and main features of these dislocations, especially the vortex linkages over the dislocations, are clearly described by tracing the substantial modification of vorticity lines and other key flow quantities. Local irregularities in the variations of velocity, vorticity and frequency, and transition behavior of the wake flows are analyzed by wavelet analysis and the proper orthogonal decomposition (POD) method.