Abstract
The laminar-turbulent transition of a boundary layer induced by jet flow injection in the inlet region of a circular pipe was experimentally investigated with hot-wire anemometer. The jet flow was periodically inserted radially from a small hole in the inlet region into the pipe flow. The threshold value of the jet flow rate to generate the turbulent patch was then obtained. The threshold value decreased and saturated finally with the increase in jet flow duration. The normalized jet flow duration when the threshold value was saturated increased with the increase in Reynolds number, contrary to the developed region. The normalized threshold flow rate tended to vary with the Reynolds number among three regions. All tendencies were different from those of the developed region. With the increase in jet flow rate beyond the threshold value, the duration of the turbulent patch increased, though the fluctuating velocity within the patch did not.
