抄録
Laminar-Turbulent transition of a boundary layer induced by a single roughness element in the inlet region of a circular pipe was experimentally investigated. Mean and fluctuating velocity components in the axial direction were measured by a hot-wire anemometer. The Reynolds number based on the pipe diameter and the bulk velocity was 20 000. A stationary turbulent region was formed downstream of the roughness element. The contour lines of the turbulent region were wedge-shaped once they unfolded onto a flat plane. The virtual origin of the turbulent region equaled the roughness position. The contour lines of intermittency, which were initially staight, then curved to the outside. This condition is similar to that of the turbulence wedge on a flat plate. The fluctuating velocity was as its maximum not at the center of the region but at an interface region between the turbulent region and surrounding laminar region. The fluctuation within the interface region was large.
