Turbulence and turbulent transport in sediment-laden open-channel flows
Creators: name: Lyn, Dennis Anthony
Publisher: name: California Institute of Technology
Year: 1986

description: Some aspects of turbulence in sediment-laden open-channel flows are examined. A conceptual model based on similarity hypotheses rather than the traditional mixing-length closures is proposed. It is argued that, over a wide range of laboratory conditions, the main effect of the suspended sediment on the flow is confined to a layer near the bed. If such a distinct layer can be discerned, then this is separated from the outer flow by an inertial subregion in which the mean-velocity profile is approximately logarithmic, with an associated von Kàrman constant of ≈ 0.4, i.e., the same value as in single-phase flows. It is further shown that power-law profiles may be derived from general similarity arguments and asymptotic matching. These implications contrast with those of previous models in which changes in the mean-velocity profile are supposed to occur throughout the flow or primarily in the flow far from the bed. Length and concentration scales appropriate to sediment-laden flows are suggested. 

An experimental study was also undertaken. Both the saturated case, in which a sand bed was present, and the unsaturated case, in which a sand bed was absent, were investigated. The study was restricted to nominally flat beds, composed of three well sorted sands (median grain diameters ranged from 0.15 mm to 0.24 mm). A two-component laser-Doppler-velocimetry system was used for velocity measurements. Suction sampling was used to measure local mean concentrations. The major points of the conceptual model are supported by the experimental results. Higher-order statistics of the velocity field were found to exhibit little evidence of any effect on the outer flow, supporting the view that the effect of the suspended sediment is felt primarily in the inner region. This contrasts with the predictions of recent models that propose an analogy between sediment-laden flows and weakly stable density-stratified flows.
description: Copyright ©1986 by Dennis A. Lyn. All rights reserved. 

A number of people have contributed, directly or indirectly, to the work reported here. Prof. N.H. Brooks, my advisor, suggested the general field of sediment transport as an impossible area of research, instantly seducing the innocent, and generally allowed me the freedom to go on my own wild goose chases. Vito Vanoni provided constant encouragement even when he was not, perhaps, in total agreement with all of my ideas. Jim Skjelbreia, Dimitri Papantoniou, and Panos Papanicolaou helped signally in the areas involving instrumentation, data acquisition and computing hardware. The presence of Peter Goodwin, my co-conspirator in sediment-transport intrigues, substantiated my suspicion that somebody else besides myself was still interested in sediment-transport research. Cathy van Ingen got me started on the nuts-and-bolts of experimental work, and bequeathed the essential data acquisition software. Comments on an early draft of some of the ideas in Chap. 3 by Profs. D. Coles and J. Imberger were also useful. The general critique of Prof. J. List should also be acknowledged. The artisans of the Hydraulics Lab shops, Elton Daly, Rich Eastvedt, Joe Fontana, and Leonard Montenegro, facilitated experimental work, not only by their technical prowess, but also by their agreeable character. Jeff Zeit, my fellow Canadian, introduced me to the beauties of TEX, thereby delaying the completion of this document by, at least, a couple of years. 

A possibly harrowing experience was made certainly bearable, at times pleasurable, by those with whom I came into daily contact (in addition to those already noted above): Joan (pronounced Jo-anne) Mathews, Rayma Harrison, Gunilla Hastrup, Bob Koh, Jin Jwang Wu, Liyuan Liang, Chi Kin Ting, Imad Hannoun, and of course my office mates, the departed Pratim Biswas and the still (and for some time to come) present Kit Yin Ng (pronounced ?). 

Financial support for the work reported here was provided by the National Science Foundation through grant CEE-7920311 until 1983, and grant MSM-8611127 for 1986, and by discretionary funds from the James Irvine Professorship. The author received personal support during the period 1981-82 in the form of a Haagen-Smit/Tyler Fellowship, and during the period 1982-85 from the National Science and Engineering Research Council of Canada in the form of post-graduate fellowships. This report is essentially identical to the thesis submitted by the author in September, 1986 in partial fulfillment o[ the requirements for the degree of Doctor of Philosophy. 

Lastly, I would like to dedicate this work to my mother, whose example of stoicism and perseverance stood me in good stead during the frustrations of research.