Amir H. Azimi

Discharge Characteristics of Weirs of Finite Crest Length

This technical note presents a critical analysis flow over weirs of finite crest length, with square-edged or rounded entrance, for free-flow conditions. Using the flow equation for the broad-crested weir with parallel flow in the critical state as the basis, we have defined the discharge coefficient C d , with the head on the weir as the length scale. Based on an extensive analysis of the experimental observations in the literature, we have confirmed the classification of finite crest length weirs into four classes of long-crested, broad-crested, short-crested, and sharp-crested weirs. For the square-edged entrance, we have developed robust correlations for C d when the Weber number is greater than 1. For weirs with a rounded entrance, for which the data set is not that extensive compared to the square-edged case, we have developed good correlations for C d .

Discharge Characteristics of Weirs of Finite Crest Length with Upstream and Downstream Ramps

This paper considers flow measurement in open channels with transverse weirs of finite crest length with sloping crests and upstream or downstream ramps—or both—for free flows. Using the broad-crested weir equation with a discharge coefficient as the basis and following the earlier studies of broad-crested weirs, robust correlations have been developed for the discharge coefficient by using the experimental results available in the literature. Effects of upstream and downstream ramps were studied by introducing the upstream and the downstream length scales, respectively. The proposed correlations of embankment weirs were compared with the head-discharge formu- lations of embankment weirs in the literature. Triangular (hump) weirs with either upstream or downstream ramps (or both) have also been considered. It was found that in triangular (hump) weirs, the discharge coefficient increases when the downstream slope increases, but it decreases when the upstream slope increases. DOI: 10.1061/(ASCE)IR.1943-4774.0000519.

Submerged Flows over Rectangular Weirs of Finite Crest Length

AbstractThis work presents a critical analysis of submerged flow over rectangular weirs of finite crest length. For finite crest length weirs, because the existing data sets are not extensive, new experiments for these weirs with sharp-edged and rounded crest were conducted. Based on these data, a diagram is developed to show the variation of the normalized tailwater depth with ho/L where ho is the free flow head and L is the length of the crest, to predict the onset of submergence or the modular limit. Water surface profiles of flow over weirs of finite crest length with square-edge and rounded crests were plotted to study the formation of waves in modular and submerged conditions. Characteristics length scales such as wave length and amplitude at the modularity limit and the location of the first trough downstream of the weir were measured to generalize surface profiles at different flow discharges. An empirical equation for the discharge reduction factor was also formulated. This equation has two expon...

Effect of Particle Size on the Characteristics of Sand Jets in Water

Sand jets in water have extensive engineering applications. A detailed numerical modeling of sand jets in water was conducted at high initial sand concentration using a commercial computational fluid dynamics package (ANSYS CFX 11.0). The results of the numerical simulation were first compared with some recent laboratory experiments. Simulations were then conducted to investigate the effect of sand particle sizes on velocity distribution, concentration profile, and turbulent properties. Turbulent flow characteristics, such as turbulent kinetic energy, turbulence intensity, rate of energy dissipation, and turbulent eddy frequency, were evaluated and the trend compared with the previous studies in the literature. The location of maximum kinetic energy was found to be independent of particle size. The turbulent kinetic energy and rate of dissipation of the water phase decrease with increasing particle size.

Experimental Study of Subaqueous Sand Deposition from Slurry Wall Jets

Thispaperpresentstheresultsofalaboratorystudyonthesubaqueousdepositionofsandparticlesfromsediment-ladencircularjets on horizontal and inclined beds. Four sets of experiments were carried out to investigate the effects of jet characteristics, bed slope, sediment size, and sediment concentration on the growth and development of the sediment mound. Three distinct flow regimes can be identified as de- veloping regime, spreading regime, and backup regime. It was found that in the developing regime, deposition height and width formed by the continuous release of sediment particles grow faster than the mound length. Slurry jet flow in the spreading regime was diverted from the axial direction to the sides and caused more deposition on both sides of the mound. Backup regime started when the deposition height and width reachedtheirmaximumvalues.Inthiscondition,aslurryjetpushedsedimentbacktothenozzleandeventuallyblockedthe flow.Theinitiation of sediment deposition was estimated, and predictions were compared with experimental results. Variations of the deposition length scales, moundbasearea,andangleofdepositionwithtimeweremeasured.Empiricalformulationswereintroducedtopredictdepositiondevelopment

Analysis of Slump Test for Sand–Foam Mixtures

AbstractSand–foam mixtures have many potential applications in the field of mining and construction. This paper conducts laboratory experiments to investigate rheological characteristics of sand–fo...

Experimental Study of Particle Clouds in Stagnant Water

AbstractLaboratory experiments were conducted to investigate the evolution of particle clouds in stagnant water. Nozzle size and released mass of particles were formed to an aspect ratio of Lo/do, ...

Flume experiments on baffle-posts for retarding open channel flow By Caroline Ubing, Robert Ettema and Christopher I. Thornton

The authors have written an interesting paper on the hydraulics of flow through baffle-post structures with single and double rows of unsubmerged posts. The authors studied the effects of lateral and streamwise post spacing and flow discharge on the head loss and flow depth upstream of the baffle-post structures. The discusser would like to show the use of existing data from the original paper to predict flow discharge passing through baffle-posts with one or two parallel rows of circular posts. Recently, Samani (2017) tested the possibility of flow measurement in open channels using one cylindrical or two half-cylindrical posts in rectangular, trapezoidal and circular cross sections. Similarly, Ferro (2016) provided head-discharge relationships for rectangular open channels using a central trapezoidal baffle. Using the principle of critical flow for flumes with rectangular cross sections (Ackers, White, Perkins, & Harrison, 1978), a correlation can be formulated between the water head upstream of contraction (i.e. baffle-posts) y1 and flow discharge Q as:

Hydraulics of Submerged Triangular Weirs and Weirs of Finite-Crest Length with Upstream and Downstream Ramps

AbstractLaboratory tests were carried out to investigate the hydraulics of submerged flow over triangular weirs and weirs of finite-crest length with upstream and/or downstream ramp(s). Water surfa...