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Hubert Chanson - One of the best experts on this subject based on the ideXlab platform.
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interaction between free surface aeration and total pressure on a stepped Chute
Experimental Thermal and Fluid Science, 2016Co-Authors: Gangfu Zhang, Hubert ChansonAbstract:Abstract Stepped Chutes have been used as flood release facilities for several centuries. Key features are the intense free-surface aeration of both prototype and laboratory systems and the macro-roughness caused by the stepped cavities. Herein the air bubble entrainment and turbulence were investigated in a stepped spillway model, to characterise the interplay between air bubble entrainment and turbulence, and the complicated interactions between mainstream flow and cavity recirculation motion. New experiments were conducted in a large steep stepped Chute (θ = 45°, h = 0.10 m, W = 0.985 m). Detailed two-phase flow measurements were conducted for a range of discharges corresponding to Reynolds numbers between 2 × 105 and 9 × 105. The total pressure, air–water flow and turbulence properties were documented systematically in the mainstream and cavity flows. Energy calculations showed an overall energy dissipation of about 50% regardless of the discharge. Overall the data indicated that the bottom roughness (i.e. stepped profile) was a determining factor on the energy dissipation performance of the stepped structure, as well as on the longitudinal changes in air–water flow properties. Comparative results showed that the cavity aspect ratio, hence the slope, has a marked effect on the residual energy.
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energy dissipation on embankment dam stepped spillways overflow stepped weirs and masonry stepped spillways
17th Congress of IAHR Asia and Pacific Division IAHR-APD, 2010Co-Authors: Hubert ChansonAbstract:Stepped spillways are designed to increase the rate of energy dissipation on the Chute reducing the size of a downstream energy dissipator. The prediction of the turbulent dissipation above the steps constitutes a critical part of the design process, especially at large discharges per unit width corresponding to the skimming flow regime. Herein new measurements were conducted in a large facility with a channel slope of 26.6o and step heights of 0.10 m. The experiments were performed with large discharges corresponding to Reynolds numbers ranging from 5×10 4 to 1×10 6 . The waters were highly turbulent and they dissipated a major proportion of the flow kinetic energy. Taking into account the free-surface aeration, the present results were compared with recent results on 15.9o and 21.8o slopes; the range of slopes (1V:3.5H to 1V:2H) was typical of embankment slopes and older spillway designs. The comparative results yielded some simple design guidelines applicable to masonry stepped spillways, embankment dam stepped Chutes and overflow stepped weirs.
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an experimental study of effects of step roughness in skimming flows on stepped Chutes
Journal of Hydraulic Research, 2008Co-Authors: Carolina Gonzalez, Hubert ChansonAbstract:On a spillway Chute, a stepped design increases the rate of energy dissipation on the Chute itself and reduces the size of a downstream energy dissipater. Up to date, the effects of step roughness on the flow properties remain unknown despite the practical relevance to damaged concrete steps, rock Chutes and gabions weirs. New measurements were conducted in a large-size laboratory facility with two step conditions (smooth and rough) and three types of step roughness. Detailed air-water flow properties were measured systematically for several flow rates. The results showed faster flow motion on rough step Chutes. Although the finding is counter-intuitive, it is linked with the location of the inception point of free-surface aeration being located further downstream than for a smooth stepped Chute for an identical flow rate. In the aerated flow region, the velocities on rough-step Chutes were larger than those of smooth Chute flows for a given flow rate and dimensionless location from the inception point of...
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turbulence and cavity recirculation in air water skimming flows
Journal of Hydraulic Research, 2008Co-Authors: Carlos A Gonzalez, Hubert ChansonAbstract:Current expertise in air–water turbulent flows on stepped Chutes is limited mostly to laboratory experiments at low to moderate Reynolds numbers on Chutes with flat horizontal steps. In this study, highly turbulent air–water flows skimming down a large-size stepped Chute were investigated with a 1V:2.5H slope. For some experiments, the cavity recirculation was controlled using triangular vanes, or longitudinal ribs, to enhance the interactions between the skimming flow and cavity recirculating region. New experiments were performed with seven configurations. The results demonstrated the strong influence of the vanes on the cavity recirculation patterns and on the air–water flow properties. An increase in flow resistance was observed consistently with maximum rate of energy dissipation achieved with vanes placed in a zigzag pattern.
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hydraulic design of stepped spillways and downstream energy dissipators for embankment dams
Dam Engineering, 2007Co-Authors: Carlos A Gonzalez, Hubert ChansonAbstract:In recent years, the design flows of many dams were re-evaluated, often resulting in discharges larger than the original design. In many cases, the occurrence of the revised flows could result in dam overtopping because of insufficient storage and spillway capacity. An experimental study was conducted herein to gain a better understanding of the flow properties in stepped Chutes with slopes typical of embankment dams. The work was based upon a Froude similitude in large-size experimental facilities. A total of 10 configurations were tested including smooth steps, steps equipped with devices to enhance energy dissipation and rough steps. The present results yield a new design procedure. The design method includes some key issues not foreseen in prior studies : e.g., gradually varied flow, type of flow regime, flow resistance. It is believed that the outcomes are valid for a wide range of Chute geometry and flow conditions typical of embankment Chutes.
Antonio Piersanti - One of the best experts on this subject based on the ideXlab platform.
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stresses at the base of dry and dense flows of angular rock fragments in 3 d discrete element modeling scaling of basal stress fluctuations versus grain size flow volume and channel width
Journal of Volcanology and Geothermal Research, 2018Co-Authors: Bruno Cagnoli, Antonio PiersantiAbstract:Abstract We simulate granular flows of angular rock fragments by means of a three-dimensional discrete element modeling to study the basal stresses that these flows exert on the subsurface. These granular flows have different grain sizes and different flow volumes and they model dry rock avalanches and dense pyroclastic flows. These flows travel on four different concave–upward Chutes that represent channels on a mountainside or on the flank of a volcano. Each Chute has a different width. The stress data demonstrate the validity of a linear relation between two scaling parameters: D and ψ . Parameter D is a scaled basal stress deviation that is equivalent to a scaled particle agitation. Particle agitation is ultimately responsible for the energy dissipation that governs the mobility of dense geophysical flows in nature. Parameter ψ contains grain size, flow volume and channel width. This second parameter is equal to the product of the reciprocal of characteristic numbers of fragments in granular flows. Since these numbers of particles are dimensionless, the linear relation is valid at any scale, either in the laboratory or in nature.
Carlos A Gonzalez - One of the best experts on this subject based on the ideXlab platform.
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turbulence and cavity recirculation in air water skimming flows
Journal of Hydraulic Research, 2008Co-Authors: Carlos A Gonzalez, Hubert ChansonAbstract:Current expertise in air–water turbulent flows on stepped Chutes is limited mostly to laboratory experiments at low to moderate Reynolds numbers on Chutes with flat horizontal steps. In this study, highly turbulent air–water flows skimming down a large-size stepped Chute were investigated with a 1V:2.5H slope. For some experiments, the cavity recirculation was controlled using triangular vanes, or longitudinal ribs, to enhance the interactions between the skimming flow and cavity recirculating region. New experiments were performed with seven configurations. The results demonstrated the strong influence of the vanes on the cavity recirculation patterns and on the air–water flow properties. An increase in flow resistance was observed consistently with maximum rate of energy dissipation achieved with vanes placed in a zigzag pattern.
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hydraulic design of stepped spillways and downstream energy dissipators for embankment dams
Dam Engineering, 2007Co-Authors: Carlos A Gonzalez, Hubert ChansonAbstract:In recent years, the design flows of many dams were re-evaluated, often resulting in discharges larger than the original design. In many cases, the occurrence of the revised flows could result in dam overtopping because of insufficient storage and spillway capacity. An experimental study was conducted herein to gain a better understanding of the flow properties in stepped Chutes with slopes typical of embankment dams. The work was based upon a Froude similitude in large-size experimental facilities. A total of 10 configurations were tested including smooth steps, steps equipped with devices to enhance energy dissipation and rough steps. The present results yield a new design procedure. The design method includes some key issues not foreseen in prior studies : e.g., gradually varied flow, type of flow regime, flow resistance. It is believed that the outcomes are valid for a wide range of Chute geometry and flow conditions typical of embankment Chutes.
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an experimental study of free surface aeration on embankment stepped Chutes
2005Co-Authors: Carlos A GonzalezAbstract:Stepped Chutes have been used as hydraulic structures for more than 3.5 millennia for different purposes: For example, to dissipate energy, to enhance aeration rate in the flow and to comply with aesthetical functions. They can be found acting as spillways in dams and weirs, as energy dissipators in artificial channels, gutters and rivers, and as aeration enhancers in water treatment plants and fountains. Spillways are used to prevent dam overtopping caused by floodwaters. Their design has changed through the centuries. In ancient times, some civilizations used steps to dissipate energy in open channels and dam over-falls in a similar fashion as natural cascades. However, in the first half of the twentieth century, the use of concrete became popular and the hydraulic jump was introduced as an efficient energy dissipator. In turn, the use of a stepped geometry became obsolete and was replaced with smooth Chutes followed by hydraulic jump stilling basins. In recent years, new construction techniques and materials (Roller Compacted Concrete RCC, rip-rap gabions, wire-meshed gabions, etc.) together with the development of new applications (e.g. re-aeration cascades, fish ladders and embankment overtopping protection or secondary spillways) have allowed cheaper construction of stepped Chutes, increasing the interest in stepped Chute design. During the last three decades, research in the hydraulics of stepped spillways has been very active. However, studies prior to 1993 neglected the effect of free-surface aeration. A number of studies since this time have focused on air-water flows in steep Chutes (theta approximating 50 degrees). But experimental data is still scarce, and the hydraulic performance of stepped cascades with moderate slope is not yet understood. This study details an experimental investigation of physical air-water flow characteristics down a stepped spillway conducted in two laboratory models with moderate slopes: the first model was a 3.15 m long stepped Chute with a 15.9 degree slope comprising two interchangeable-height steps (h = 0.1 m and h = 0.05 m); the second model was a 2.5 m long, stepped channel with a 21.8 degree slope comprising 10 steps (h = 0.1 m). Different arrangements of turbulence manipulators (vanes) were also placed throughout the Chute in the second model. A broad range of discharges within transition and skimming flow regimes was investigated to obtain a reliable representation of the air-water flow properties. Measurements were conducted using single and double tip conductivity probes at multiple span wise locations and at streamwise distances along the cavity between step edges to obtain a complete three-dimensional representation of the flow. Although the present study was conducted for two moderate slope Chutes (theta = 15.9 degrees & 21.8 degrees), it is believed that the outcomes are valid for a wider range of Chute geometry and flow conditions. The purpose of this study is to improve the understanding of turbulent air-water flows cascading down moderate slope stepped Chutes, and gain new understandings of the interactions between aeration rate, flow turbulence and energy dissipation; scale effects are also investigated. The study provides new, original insights into air-water turbulent flows cascading down moderate slope stepped spillways not foreseen in prior studies, thus contributing to improve criterion designs. It also presents an extensive experimental database (available in a CD-ROM attached at the end of this thesis) and a new design criterion that can be used by designers and researchers to improve the operation of stepped Chutes with moderate slopes. The present thesis work included a twofold approach. Firstly, the study provided a detailed investigation of the energy dissipative properties of a stepped channel, based upon detailed airwater flow characteristics measurements conducted with sub-millimetric conductivity probes. Secondly, the study focused on the microscopic scale properties of the airwater flow, using the experimental data to quantify the microscopic scale physical processes (e.g. momentum transfer, shear layer development, vertical mixing, airbubbles/water-droplets break-up and coalescence etc.) that are believed to increase the flow resistance in stepped canals. The study highlighted the tridimensionality of skimming flows and hinted new means of enhancing flow resistance by manipulating turbulence in the stepped Chute. Basic dimensional analysis results emphasized that physical modelling of stepped Chutes is more sensitive to scale effects than classical smooth-invert Chute studies and thus suggested that the extrapolation of results obtained from heavily scaled experimental models should be avoided. The present study also demonstrated that alterations of flow recirculation and fluid exchanges between free-stream and cavity flow affects drastically form losses and in turn the rate of energy dissipation. The introduction of vanes demonstrated simple turbulence manipulation and form drag modification that could lead to more efficient designs in terms of energy rate dissipation without significant structural load on the stepped Chute.
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physical modelling and scale effects of air water flows on stepped spillways
Journal of Zhejiang University Science, 2005Co-Authors: Hubert Chanson, Carlos A GonzalezAbstract:During the last three decades, the introduction of new construction materials (e.g. RCC (Roller Compacted Concrete), strengthened gabions) has increased the interest for stepped channels and spillways. However stepped Chute hydraulics is not simple, because of different flow regimes and importantly because of very-strong interactions between entrained air and turbu- lence. In this study, new air-water flow measurements were conducted in two large-size stepped Chute facilities with two step heights in each facility to study experimental distortion caused by scale effects and the soundness of result extrapolation to pro- totypes. Experimental data included distributions of air concentration, air-water flow velocity, bubble frequency, bubble chord length and air-water flow turbulence intensity. For a Froude similitude, the results implied that scale effects were observed in both facilities, although the geometric scaling ratio was only Lr=2 in each case. The selection of the criterion for scale effects is a critical issue. For example, major differences (i.e. scale effects) were observed in terms of bubble chord sizes and turbulence levels al- though little scale effects were seen in terms of void fraction and velocity distributions. Overall the findings emphasize that physical modelling of stepped Chutes based upon a Froude similitude is more sensitive to scale effects than classical smooth-invert Chute studies, and this is consistent with basic dimensional analysis developed herein.
A W Roberts - One of the best experts on this subject based on the ideXlab platform.
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modelling bulk solid interactions in transfer Chutes accelerated flow
Chemical Engineering Science, 2019Co-Authors: Dusan Ilic, A W Roberts, Craig WheelerAbstract:Abstract The continuum method is an approach to model transfer Chutes characterised by accelerated flow conditions, with origins stemming from free flowing materials. Physical bulk solid properties obtained through laboratory tests are incorporated and the focus is to maintain a rapidly moving stream, with minimum variation in velocity across the burden depth. Due to structural elements, it is difficult to quantify flow occurring inside and as such, accurate site validation is scarce. Discrete Element Modelling (DEM) provides a solution enabling flow visualisation, and a unique means of both qualitative and quantitative analyses. This paper presents application of both methods in a real high throughput installation comprising a bifurcated Chute arrangement transferring coal from one delivery conveyor to two receiving conveyors. The results show that both methods can model the type of flow exhibited and presented is a comparison between qualitative site observations and material flow profiles calculated using each method.
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modelling bulk solid flow interactions in transfer Chutes shearing flow
Powder Technology, 2019Co-Authors: Dusan Ilic, Craig Wheeler, A W Roberts, Andre KatterfeldAbstract:Abstract In the field of handling, storage and transportation, Chutes are used to transfer bulk solids between conveyors. In these systems, traditional analysis methods based on the principle of continuum mechanics approximate an accelerated stream that incorporates physical bulk solid properties obtained from standardised tests. Due to difficulties in physically observing the flow within the transfer structure, verification of the method at full scale is scarcely reported. In contrast, Discrete Element Modelling (DEM) allows flow visualization through a transfer Chute and enables qualitative and quantitative analysis provided accurate simulation parameters are selected. This paper presents application of the two methods in a real life high throughput installation using a case study comprising of a stacker Chute system transferring coal from one incoming conveyor to one outgoing (boom) conveyor. The flow analysed is representative of transfer configurations characterised by a re-directed fast moving, high volume stream in restricted space, where the mode of flow is governed by internal (shear) properties of the bulk solid material. For the study, the velocity of the coal stream on the outgoing conveyor at loading is significantly lower compared to both the incoming and outgoing conveyor belt speeds. In the study presented, application of the traditional and a modified continuum method approach is compared to DEM simulations and site observations. A sensitivity analysis of modelling parameters is also provided.
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evaluation of dust emissions from conveyor transfer Chutes using experimental and cfd simulation
International Journal of Mineral Processing, 2012Co-Authors: X L Chen, Craig Wheeler, T J Donohue, Rachael Mclean, A W RobertsAbstract:Abstract This paper focuses on a study concerned with reducing dust emissions from belt conveyor transfer Chutes in bulk material handling plants. Several transfer Chute configurations were investigated with the aim of analysing the system performance. Scale model laboratory testing was undertaken to determine the effectiveness of each design in reducing dust emission. Computational Fluid Dynamics (CFD) was used to investigate the flow pattern of the granular material and entrained air in each of the transfer Chute configurations. To verify the feasibility of CFD for dust emission prediction, a two-phase three-dimensional Euler–Euler model was adopted to qualitatively predict the performance of six transfer Chute configurations with respect to dust generation. The predicted dust emissions obtained from the simulations were compared with the scale model test results. The simulation predictions compared favourably with the experimental results, demonstrating that CFD can be used to qualitatively evaluate the performance of transfer Chute designs with regard to dust emission.
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Chute performance and design for rapid flow conditions
Chemical Engineering & Technology, 2003Co-Authors: A W RobertsAbstract:Many industrial Chute applications are characterised by rapid flow conditions in which the bulk solid stream thickness or depth is less than the Chute width. Under these conditions, it is possible to describe the stream flow by means of a lumped parameter model which takes into account the frictional drag around the Chute boundaries as well as making allowance for inter-particle friction. Equations of motion to describe the Chute flow are presented and their application to the determination of Chute profiles to achieve optimum flow is illustrated. By means of design examples, the problems associated with the feeding of bulk solids onto belt conveyors and conveyor transfers are discussed. Criteria for the selection of the most appropriate Chute geometry to minimise Chute wear and belt wear at the feed point are presented. The determination of optimum Chute profiles to achieve specified performance criteria is outlined.
M G Kleinhans - One of the best experts on this subject based on the ideXlab platform.
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bifurcation instability and Chute cutoff development in meandering gravel bed rivers
Geomorphology, 2014Co-Authors: Wout M Van Dijk, F Schuurman, Wietse I Van De Lageweg, M G KleinhansAbstract:Chute cutoffs reduce sinuosity of meandering rivers and potentially cause a transition from a single to a multiple channel river. The channel bifurcation of the main channel and the mouth of the incipient Chute channel controls sediment and flow partitioning and development of the Chute. Recent channel bifurcation models suggest that upstream bend radius, gradient advantage, inlet step, and upstream sediment supply at the bifurcation are important factors in the evolution of bifurcations. Our objective is to unravel the relative importance of these factors for Chute cutoff success and development. We compare results from a morphodynamic three-dimensional (3D) model and a one-dimensional (1D) model with nodal-point relation with field observations of Chute cutoffs in a meandering gravel-bed river. The balance between increased gradient advantage and flow curvature upstream of the Chute channel bifurcation was systematically investigated with the 1D model. The 3D model runs and the field observations show the development of two types of Chute cutoffs: a scroll-slough cutoff and a bend cutoff. The morphodynamic 3D model demonstrates that Chutes are initiated when flow depth exceeds the floodplain elevation. Overbank flow and a significant gradient advantage result in a bend cutoff. The outcome of the 1D model shows that channel curvature at the bifurcation determines the success or failure of the Chute cutoff when the Chute channel is located at the inner bend, as in the case of scroll-slough cutoffs. We conclude that Chute initiation depends on floodplain characteristics, i.e., floodplain elevation, sediment composition, and the presence of vegetation. Chute cutoff success or failure is determined by the dynamics just upstream of the channel bifurcation and location of the Chute channel in the bend, which determines channel curvature and gradient advantage. These findings have ramifications for the prediction of Chute cutoff in a wide range of rivers under natural and managed conditions and for the understanding of stratigraphy and architecture of deposits.
