Generation and Growth of Puff and Slug in Initial Stage of a Transitional Pipe Flow.

Abstract

Generation and growth of an isolated turbulent puff and slug in the initial stage of a transitional pipe flow were investigated by LDV measurement, wall pressure measurement and flow visualization. The LDV measurement was carried out using the straight glass tube of diameter D=5.02 mm and i total length L=2576 mm, and the wall pressure measurement was done using the glass tube of D= 2.61 mm and L=1527 mm. Manipulative disturbance necessary to produce the puff and slug was provided by several kinds of ring-shaped roughness elements, installed at downstream locations of 40D, 77D and 120D from the entrance of the tube. Visualization photography of the puff and slug was synchronized with the LDV signal or the wall pressure signal. The critical Reynolds number, which was defined at the initiation of generation of the puff or the slug, changed abruptly in a range of 1 to 2 of the ratio of the momentum thickness at the location of the roughness element to the height of the roughness element. Propagation speeds of both the leading and trailing edges of the puff and slug could precisely be detected by the wall pressure measurement.