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A wind tunnel experiment was performed to investigate the requirements for providing a suitable environment for easily creating a localized turbulent region in a laminar boundary layer. A combination of a short-duration jet and suctions was used to prepare a potentially unstable region upstream, and another jet was ejected downstream against the region at various timings and different relative spanwise locations. Based on the results, the combination of the potentially unstable region and the short-duration jet promoted the transition to turbulence only under limited conditions, whereas in most cases, it worked negatively. However, the turbulent spot generation was enhanced when the downstream jet was used at the timing and location that enlarged the low-velocity area created upstream. Moreover, the locally disturbed region generated by the combination of the potentially unstable region and the short-duration jet did not directly grow into a turbulent spot; rather, the turbulent spot grew in the region following the disturbed region.

A wind tunnel experiment was performed to investigate the suitable conditions in which a localized turbulent region can easily be generated in a flat-plate boundary layer. An artificial disturbance of zero-mass flux was introduced upstream using a combination of a short-duration jet and suctions to prepare a potentially unstable environment. The disturbed region by itself decayed downstream. Another jet was then ejected downstream at several different timings and two different spanwise locations relative to the passage of the locally disturbed region to promote transition to turbulence. Although the jet was too weak to trigger the turbulence transition by itself, an isolated turbulent region, the so-called turbulent spot, was generated when ejected against the disturbed region. The optimum conditions were found when the jet was ejected between the high- and low-speed areas of the convecting unstable region.