Pipe flow

About: Pipe flow is a research topic. Over the lifetime, 13826 publications have been published within this topic receiving 351605 citations.

Experiments on transition to turbulence in oscillatory pipe flow

Abstract: A laser-Doppler velocimeter is used to analyse volume-cycled oscillatory flow of a Newtonian viscous fluid in a straight circular tube. The axial velocity is measured at radial positions across the diameter of the tube for a wide range of amplitude A = stroke distance/tube radius (2.4 [les ] A [les ] 21.6) and Womersley parameter (9 < α < 33). Transition to turbulence is detected during the decelerating phase of fluid motion for 500 < Rδ < 854, where Rδ = αA √2 is the Reynolds number based on Stokes-layer thickness. The turbulence is confined to an annular region which is a few times the Stokes-layer thickness near the wall. Hot-film anemometer measurements indicate the core flow remains stable when the boundary layer becomes turbulent for Rδ up to 1310.

Vortex dynamics and the production of Reynolds stress

Abstract: The physical mechanisms by which the Reynolds shear stress is produced from dynamically evolving vortical structures in the wall region of a direct numerical simulation of turbulent channel flow are explored. The complete set of quasistreamwise vortices are systematically located and tracked through the flow by the locus of the points of intersection of their centres of rotation with the (y, z) numerical grid planes. This approach assures positive identification of vortices of widely differing strengths, including those whose amplitude changes significantly in time. The process of vortex regeneration, and the means by which vortices grow, distort and interact over time are noted. Ensembles of particle paths arriving on fixed planes in the flow are used to represent the physical processes of displacement and acceleration transport (Bernard & Handler 1990a) from which the Reynolds stress is produced. By interweaving the most dynamically significant of the particle paths with the evolving vortical structures, the dynamical role of the vortices in producing Reynolds stress is exposed. This is found to include ejections of low-speed fluid particles by convecting structures and the acceleration and deceleration of fluid particles in the cores of vortices. Sweep dominated Reynolds stress close to the wall appears to be a manifestation of the regeneration process by which new vortices are created in the flow.

Drag Reduction by Spanwise Wall Oscillation in Wall-Bounded Turbulent Flows

Abstract: Drag reduction in turbulent channel and pipe e ows by spanwise (circumferential) wall oscillations is studied numerically. The ine uence of the wall oscillation on near-wall streamwise vortices is examined. By the use of the Stokes second problem, a wall-normal distanceparameter and an acceleration parameterare obtained toestimate the drag reduction rate. A simple equation is derived for expressing the drag reduction rate by spanwise wall oscillations. The relation between near-wall streamwise vortices and low- and high-speed e uids is scrutinized to extract the key parameters. The drag reduction mechanism is analyzed in terms of the attenuation of Reynolds shear stress.

Flow in Rough Conduits

Abstract: A new concept of flow over rough pipe and channel surfaces is presented. The concept is based particularly on the effect of the longitudinal spacing of surface-roughness elements and their associat...