Pipe flow

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

High-frequency self-excited oscillations in a collapsible-channel flow

Abstract: High-Reynolds-number asymptotics and numerical simulations are used to describe two-dimensional, unsteady, pressure-driven flow in a finite-length channel, one wall of which contains a section of membrane under longitudinal tension. Asymptotic predictions of stability boundaries for small-amplitude, high-frequency, self-excited oscillations are derived in the limit of large membrane tension. The oscillations are closely related to normal modes of the system, which have a frequency set by a balance between membrane tension and the inertia of the fluid in the entire channel. Oscillations can grow by extracting kinetic energy from the mean Poiseuille flow faster than it is lost to viscous dissipation. Direct numerical simulations, based on a fully coupled finite-element discretization of the equations of large-displacement elasticity and the Navier–Stokes equations, support the predicted stability boundaries, and are used to explore larger-amplitude oscillations at lower tensions. These are characterized by vigorous axial sloshing motions superimposed on the mean flow, with transient secondary instabilities being generated both upstream and downstream of the collapsible segment.

Flow in an Axially Rotating Pipe : A calculation of flow in the saturated region

Abstract: If a flow enters an axially rotating pipe, it receives a tangential component of velocity from the moving wall, and the flow pattern and hydraulic loss suffer a change according to the ratio of the rotational speed to the through flow velocity. A flow laminarization is set up by an increase in the rotational speed of the pipe if the flow in the pipe is initially turbulent, and a flow destabilization is brought conversely about if the flow is initially laminar. Velocity distributions and friction coefficient in the fully developed region of the pipe were calculated by using a modified mixing length theory, and the results were compared with those by the experiments.

Three indirect methods for the drag characterization of arbitrarily rough surfaces on flat plates

Abstract: Three indirect methods for characterizing the drag of an arbitrarily rough surface on a flat plate are derived or rederived from the similarity laws of turbulent shear flows These are: (1) the well- known procedure using displacement thickness; (2) the probably not- so-well-known procedure using total drag; and (3) a proposed new procedure using only the freestream velocity and a local shear stress The classical indirect procedure for pipe flow is also derived to show a commonality with the flat-plate methods

Separation and reattachment of non-newtonian fluid flows in a sudden expansion pipe

Abstract: In the current flow visualization studies, the role of non-Newtonian characteristics (such as shear-rate-dependent viscosity and viscoelasticity) on flow behavior across the sudden expansion step in a circular pipe is investigated over a wide range of Reynolds numbers including the turbulent flow. The expansion ratios tested are 2.000 and 2.667 and the range of the Reynolds number covered in the current flow visualization tests are 10–35 000 based on the inlet diameter. The reattachment lengths for the viscoelastic fluids in the laminar flow regime are found to be much shorter than those for the Newtonian fluid. In addition they decrease significantly with increasingly concentration of viscoelastic fluid at the same Reynolds number. However, in the turbulent flow regime, the reattachment length for the viscoelastic fluids is two or three times longer than those for water, and gradually increases with increasing concentration of viscoelastic solutions, resulting in 25 and 28 step-height distances for 500 ppm and 1000 ppm polyacrylamide solutions respectively. This may be because the elasticity in polyacrylamide solutions suppresses the eddy motion and controls separation and reattachment behavior in the sudden expansion pipe flow. The reattachment lengths for the purely viscous non-Newtonian fluids are found to be almost the same as those for water.