TRANSIENT, TURBULENT, SMOOTH PIPE FRICTION

Citation
Ae. Vardy et Jmb. Brown, TRANSIENT, TURBULENT, SMOOTH PIPE FRICTION, Journal of Hydraulic Research, 33(4), 1995, pp. 435-456
Citations number
19
Categorie Soggetti
Water Resources","Engineering, Civil
ISSN journal
00221686
Volume
33
Issue
4
Year of publication
1995
Pages
435 - 456
Database
ISI
SICI code
0022-1686(1995)33:4<435:TTSPF>2.0.ZU;2-A
Abstract
Two of the most promising analytical models of unsteady friction in tu rbulent pipe flows are based on sharply contrasting hypotheses. One us es the history of the flow; the other uses instantaneous conditions. T he purposes of this paper are to present an analysis using the former approach and to indicate how to determine which of the two methods is appropriate. A weighting function model of transient friction is devel oped for flows in smooth pipes by assuming the turbulent viscosity to vary linearly within a thick shear layer surrounding a core of uniform velocity and is thus applicable to flows at high Reynolds number. In the case of low Reynolds number turbulent flows and short time interva ls, the predicted skin friction is identical to an earlier model devel oped by Vardy et al (1993). In the case of laminar flows, it gives res ults equivalent to those of Zielke (1966, 1968). The predictions are c ompared with analytical results for the special case of flows with uni form acceleration. It is this case that enables clarifying comparisons to be drawn with ''instantaneous'' methods of representing transient skin friction.