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An open channel flume with a central 180-degree bend with a rigid bed is designed to obtain a better understanding of the complex flow pattern around a T-shaped spur dike located in a sharp bend. The 3-dimensional velocities are measured by using an acoustic Doppler velocimetry under clear-water conditions. This study’s primary objective is to compare variations of the mean flow pattern along a 180-degree bend with a variety of T-shaped spur dike lengths. In order to do so, parameters such as streamlines, the maximum velocity distribution, and the secondary flow strength under the influence of three T-shaped spur dike lengths will be analyzed and then compared with the case where no spur dikes are implemented. The results show that with the spur dike placed at the bend apex, the mean secondary flow strength at that range increases by approximately 2.5 times. In addition, a 67% increase in the length of the wing and web of the spur dike leads to a 27% growth in the mean secondary flow strength along the bend.

It is common for engineers to use countermeasures to protect hydraulic structures against scour. This study aims to explore the effect of jet injection through the pier body as a pier-scour countermeasure. Laboratory experiments were conducted in two different flow depths (10.5 and 28 cm) using 1-jet and 3-jet injections, different jet locations, and angles between the jets under clear-water conditions. The experimental data showed that the most optimal case in terms of pier-scour depth reduction occurred for lower flow depth, higher jet flow rate, and angle between the jets equal to 90°. Moreover, the jets are able to reduce the scour depth, scour volume and upstream slope of the scour hole up to 37.5%, 57%, and 25% for flow depth of 10.5 cm and 31.2%, 37%, and 57% for flow depth of 28 cm, respectively. By increasing the number of jets, turbulent kinetic energy increases, leading to the pier-scour depth decreasing. Key words: bridge pier, local scour, jet injection, scour countermeasure. Les ingenieurs utilisent souvent des mesures de prevention pour proteger les structures hydrauliques contre l'affouillement. La presente etude explore l'effet de l'injection de jets a travers la structure du pilier en tant que mesure contre l'affouillement aux piliers. Des experiences en laboratoire ont ete realisees a deux profondeurs d'ecoulement differentes (10,5 et 28 cm) en utilisant des injections a un et trois jets, divers emplacements de jets et differents angles entre les jets sous des conditions d'eau claire. Les donnees experimentales montrent que le cas le plus optimal en termes de reduction de la profondeur d'affouillement au pilier survenait a la plus faible profondeur d'ecoulement, au debit de jet le plus elevee et a un angle de 90° entre les jets. De plus, les jets peuvent aider a reduire la profondeur d'affouillement, le volume d'affouillement et la pente amont du trou d'affouillement jusqu'a 37,5 %, 57 % et 25 % respectivement pour une profondeur d'ecoulement de 10,5 cm, et 31,2 %, 37 % et 57 % pour une profondeur d'ecoulement de 28 cm. En augmentant le nombre de jets, l'energie cinetique turbulente augmente, engendrant une diminution de la profondeur d'affouillement aux pieux. [Traduit par la Redaction] Mots-cles: pilier de pont, affouillement local, injection de jet, mesure contre l'affouillement., 1. Introduction Local scour is the process whereby sediment is removed from the base or toe of a structure by waves and currents. This is different from general bed erosion [...]

The paper reports on an experimental investigation concerning two important issues: (1) local scour and (2) riprap stability at a 45[degrees] wing-wall abutment in a degrading river bed of noncohesive sediment. The abutment considered was short (that is abutment length/flow depth CE Database subject headings: Abutments; Degradation; Erosion; Scour; Riprap; Streambeds.

The influence of bed suction on the characteristics of turbulent open channel flow is studied in a laboratory flume using a two-component laser Doppler velocimeter. The experimental results show how bed suction significantly affects the mean flow properties, turbulence levels, and Reynolds stress distributions. The data reveal the presence of a more negative vertical (downward) velocity. The results also show how the horizontal and vertical turbulence intensities and Reynolds shear stresses respond to suction. All these properties are found to reduce with increasing relative suctions: decreasing more rapidly around the bed region than that near the free surface. In the downstream direction, the flow structure in the suction zone undergoes a process of rapid readjustment within a transitional region. Beyond this region, the turbulence flow structures asymptotes toward an 'equilibrium' region. CE Database subject headings: Turbulence; Suction; Open channel flow; Velocity profile; Reynolds stress.

This note presents an experimental study of seepage effects on the dimensions of a dune: its height, length and lee-side slope. The critical slope of a cohesionless material was found to be related to the ratio of the hydraulic gradient of seepage to its critical value under the quick condition. The theoretical relationship is successfully used to predict seepage effects on the lee-side slope of dunes. Measured laboratory data support the assumption that the effect of seepage on the lee-side slope of dunes is the same as that on the critical slope of the sediment. The data reveal that the slope is reduced and increased with injection and suction, respectively. Additionally, the study explores seepage effects on the development of dune height and length. Experimental results show that suction and injection increase and decrease the equilibrium height of dunes by 25 and 40%, respectively. On the other hand, the dune length is found to increase by approximately 30% and decrease by 20% under the influence of suction and injection, respectively. DOI: 10.1061/(ASCE)0733-9429(2007)133:5(560) CE Database subject headings: Seepage; Bedforms: Dunes: Sediment transport; Hydraulic engineering.

The experimental study examines local scouring and riprap stability at bridge piers in rivers subject to bed degradation. The data show that the equilibrium bed profile associated with that with or without a pier is essentially the same, except for the obvious section around the pier. Total scour depth is shown to be the sum of bed degradation and pier scour depth. The latter can be computed from the time-average live-bed scour depth associated with the undisturbed velocity ratio before bed degradation. The experimental data also show that pier-scour depth is invariant with time, for t [greater than or equal to] 24 h. In a degrading channel, riprap around a pier will eventually develop into a stable mound when the bed shear stresses reduce with bed degradation. An auxiliary test shows that the mound is very vulnerable to another designed flood flow accompanied by large dunes. This type of riprap instability may be called bed-degradation induced failure. CE Database subject headings: Scour; Riprap; Bridges; Piers; Degradation; Sediment transport.

This study investigates theoretically and experimentally the velocity distributions of turbulent open channel flow with bed suction. A velocity profile with a slip velocity at the bed surface and an origin displacement under the bed surface is proposed and discussed. Based on this assumption, a modified logarithmic law is derived. The measured experimental velocity distribution verifies the accuracy of the theoretically derived profile. The data show a significant increase in the near bed velocity and a velocity reduction near the water surface, resulting in the formation of a more uniform velocity distribution. The values of the origin displacement, slip velocity and shear velocity are found to increase with increasing relative suction. The measured data show the occurrence of two flow regions in the suction zone: a transitional region in which the velocity readjusts rapidly; and an 'equilibrium' region. CE Database subject headings: Velocity distribution; Open channel flow; Suction; Channel beds.

The experimental study shows how an open-channel flow would respond to a sudden change (from smooth to rough) in bed roughness. Using a two-dimensional acoustic Doppler velocimeter and a laser Doppler velocimeter, the velocity, turbulent intensities, and Reynolds stress profiles at different locations along a laboratory flume were measured. Additionally, the water surface profile was also measured using a capacitance-type wave height meter. The experimental data show the formation of an internal boundary layer as a result of the step change in bed roughness. The data show that this boundary layer grows much more rapidly than that formed in close-conduit flows. The results also show that the equivalent bed roughness, bed-shear stress, turbulent intensities, and Reynolds stress change gradually over a transitional region, although the bed roughness changes abruptly. The behavior is different from that observed in close-conduit flows, where an overshooting property--which describes the ability of the bed-shear stress to attain a high-peak value over the section with the larger roughness, was reported. A possible reason for the difference is the variation of the water surface profile when an open-channel flow is subjected to a sudden change in bed roughness. CE Database keywords: Open channel flow; Bed roughness; Velocity; Turbulence.

This paper presents a semianalytical model for the radial distribution of the solid concentration in a fully developed vertical turbulent pipe two-phase flow. A simplified momentum equation in the radial direction for solid phase in a two-phase flow with dilute suspended particles was first obtained. A linear empirical closure relation for the mean gas and solid velocities along the pipe direction was constructed using published experimental data. By incorporating the closure relation, an analytical solution to the simplified solid momentum equation with the appropriate boundary conditions at the pipe center and wall was obtained. The results from this semianalytical model are able to describe the core-annulus phenomenon commonly occurring in two-phase turbulent pipe flows. Very good agreements were found between the model predictions and published experimental data. DOI: 10.1061/(ASCE)0733-9399(2002)128:4(487) CE Database keywords: Solids; Concentration; Pipe flow; Particles; Two-phase flow.