Abstract
AbstractThe validity of assumed frozen-viscosity conditions underpinning an important class of theoretical models of unsteady wall shear stress in transient flows in pipes and channels is assessed using detailed computational fluid dynamics (CFD) simulations. The need for approximate one-dimensional (1D){x,t} models of the wall stress is unavoidable in analyses of transient flows in extensive pipe networks because it would be economically impracticable to use higher order methods of analysis. However, the bases of the various models have never been established rigorously. It is shown herein that a commonly used approach developed by the first authors is flawed in the case of smooth-wall flows although it is more plausible for rough-wall flows. The assessment process is undertaken for a particular, but important, unsteady flow case, namely, a uniform acceleration from an initially steady turbulent flow. First, detailed predictions from a validated CFD method are used to derive baseline solutions with which...
Highlights
Introduction and Outline of PaperThe simulation of unsteady fluid flows in extensive pipe or duct networks such as water supply, sewerage, oil and gas lines, and railway tunnels is nearly always undertaken using one-dimensional ð1DÞfx; tg methods in which no explicit account is taken of lateral variations in a cross section
There are cases when the consequences of 2D/3D flow phenomena are of special importance
Three characteristically different phases of turbulence response to a suddenly imposed constant acceleration of an initially steady, smooth-wall pipe flow have been described with particular reference to implications for existing methods of modeling unsteady wall shear stress in 1Dfx; tg software using frozen-viscosity hypotheses
Summary
The simulation of unsteady fluid flows in extensive pipe or duct networks such as water supply, sewerage, oil and gas lines, and railway tunnels is nearly always undertaken using one-dimensional ð1DÞfx; tg methods in which no explicit account is taken of lateral variations in a cross section. This is a practical necessity because the use of two-dimensional (2D) and three-dimensional (3D) methods would be prohibitively time-consuming. The response of wall shear stresses depends strongly on the relationship between turbulence timescales and bulk-flow timescales (e.g., Ghidaoui et al 2002)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
