Flow turbulence over fixed and weakly mobile gravel beds

Citation
V. Nikora et D. Goring, Flow turbulence over fixed and weakly mobile gravel beds, J HYDR ENG, 126(9), 2000, pp. 679-690
Citations number
55
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Civil Engineering
Journal title
JOURNAL OF HYDRAULIC ENGINEERING-ASCE
ISSN journal
0733-9429 → ACNP
Volume
126
Issue
9
Year of publication
2000
Pages
679 - 690
Database
ISI
SICI code
0733-9429(200009)126:9<679:FTOFAW>2.0.ZU;2-I
Abstract
Characteristics of turbulence structure in quasi-2D flows with static and w eakly mobile gravel beds are presented. Three sets of measurements with aco ustic Doppler velocimeters in an irrigation canal were used: two with subcr itical bed shear stress (static beds) and one with the bed shear stress tau (o) close to critical tau(oc) (weakly mobile bed). The analyses included ve rtical distributions of local mean velocities, turbulence intensities, turb ulent shear stresses, velocity auto- and cross-spectra, the quadrant method , and high-order velocity moments. A number of properties of turbulence int ensities, high-order moments, streamwise bursting parameters, and velocity spectra appeared to be similar fur all three flows, but some properties wer e different. The most important one was an observed reduction in the von Ka rman constant for the flow with weakly mobile bed. Comparison of these resu lts with other studies and analogies with drag-reducing flows suggest that at tau(o)/tau(oc) approximate to 1 the drag on the bed for a given granular material should be minimized.