Laminar–turbulent transition in Poiseuille pipe flow subjected to periodic perturbation emanating from the wall. Part 2. Late stage of transition

Abstract

Transition in a fully developed circular pipe flow was investigated experimentally by introducing periodic perturbations. The simultaneous excitation of helical modes having indices m = ±1, ±2 and ±3 was chosen. The experiments revealed that the late stage of transition is accompanied by the formation of streaky structures that are associated with peaks and valleys in the azimuthal distribution of the streamwise velocity disturbance. The breakdown to turbulence starts with the appearance of spikes in the temporal traces of the velocity. Spectral characteristics of these spikes and the direction of their propagation relative to the wall are similar to those in boundary layers. Analysis of the data suggests the existence of a high-shear layer in the instantaneous velocity profile.Additional experiments in which a very weak, steady flow was added locally to the periodic axisymmetric perturbation were also carried out. These experiments resulted in the generation of a single peak in the azimuthal distribution of the disturbance amplitude. The characteristics of the transition process (spikes, vortical patterns etc.) within this peak were similar to ones observed in the helical excitation experiments. Based on these results one may conclude that late stages of transition in a pipe flow and in a boundary layer are similar. The present report is part of an ongoing investigation that was initiated by Eliahou, Tumin & Wygnanski (1998a).

Osborne Reynolds pipe flow: Direct simulation from laminar through gradual transition to fully developed turbulence

“…This similarity was conjectured and argued for in ref. 24 based on interpretation of ensemble-averaged hot-wire signals; here our DNS provides direct, convincing, time-accurate, 3D evidence (see also Movie S3). Although the breakdown of the scalar field in Fig.…”

The temporal evolution of neutral modes in the impulsively started flow through a circular pipe and their connection to the nonlinear stability of Hagen–Poiseuille flow

“…O'Sullivan & Breuer 1994) have reproduced qualitatively some of the key phenomena observed in experiments, such as the generation of puffs and slugs of vorticity (Wygnanski & Champagne 1973). A review of the many experimental studies that have been performed can be found in a recent paper by Han, Tumin & Wygnanski (2000).…”

The initial stage of transition in pipe flow: role of optimal base-flow distortions

“…Recently, much progress has been made in our understanding of the late stage of transition. Both experiments (Han, Tumin & Wygnanski 2000) and numerical simulations (Reuter & Rempfer 2000) have shown that in pipe flow this late stage is accompanied by the formation of -like vortices characterized by strong shear layers and by spikes in the temporal traces of the velocity. These spikes are associated to ring-like vortices that separate from the tips of the large -vortices.…”