抄録
A spot had a highly reproducibility in its velocity perturbations during the initial stage of its downstream development. Thus, we called it a "laminar spot". The purpose of this study was to investigate the generation and the development of an irregularity observed in the velocity waves during the laminar-turbulent transition of the spot. The results obtained show that the lateral distortion of velocity profile due to the vortex-interaction caused the irregularity of the velocity-wave amplitude in the boundary between the low- and high-speed regions in the spot. In addition, the crossover of legs of the longitudinal vortices occurred incidentally in the spot and generated a local ejection of low-momentum fluid. Afterwards, some crossovers of legs were produced in a chain reaction. Consequently, the reproducibility in the velocity waves disappeared almost in the downstream and turbulent regions increased rapidly everywhere in the spot.
