Further observations on transition in a pipe

Turbulent structures resulting from the perturbation of a fully developed linear flow in a pipe have been observed experimentally at Re 1700-4000. It is found that puffs and slugs generated by the disturbance are identical to the structures observed during the transition in the inlet region of the pipe. The transitional structure depends on the Reynolds number. Thus, puffs are generated at Re less than 2200, while slugs occur at Re greater than 2600. The slugs are shown to consist of a number of puffs which split and merge to form a larger turbulent structure.