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Experimental Study Of The Energy Dissipation In The Stepped Channels: Comparison With The Empirical Model

Congress: 2015
Author(s): Mostefa Gafsi (Laghouat, Algeria), Kettab Ahmed, Djehiche Abdelkader, Benmamar Saadia, BENNAi‡AR Naoual
Ecole Nationale Polytechnique Alger (ENP),1, Research Laboratory of Civil Engineering: RLCE, ResearchTeam2, Centre d’Étude et de recherches sur le Droit des Activités Maritimes et de l’Environnement3

Keyword(s): Sub-theme 10: Management of water resources,
AbstractAbstract We made an experimental approach in the laboratory of civil engineering at the University of Laghouat (Algeria), in three (03) models: model A (4cm x 7.5cm 4cmx) and model B (8cm x 7.5cm 8cmx), and the third model C size (12cm x 12 cm x 7.5 cm) developed "Plexiglas." In what follows, we set the rate of flow and vary the slope of the channel. Three slopes were studied in this experiment: a = 15, 30 ° and a = 45 ° for the model A, and a = 20 °, 30 ° and 45 ° for the models B and C. The simulated flows range from 0.072 l/s to 2.569 l/s. As result, the effect of the rate flow allowed us to see that: For low flows, the energy dissipation (nappe flow) is maximum is around 95% for the three models. For a large flow, the energy dissipation (nappe flow) is minimal and in the order of 82%, 80% and 77% for models A, B and C respectively, The energy dissipation relative maximum and minimum flows in skimming flow are of the order of 73% and 70% respectively. 1. Introduction: Several research models have distinguished themselves in the field of flow in channels stairs, among the most recent works are Benmamar (2006), Kerbache and Benmamar (2008a, 2008b, 2010, 2012), Gafsi and Benmamar (1999, 2012, 2013a, 2013b), and the most popular are those of Chanson (1994 , 1996, 1997, 2000) and Chanson et al (2000, 2002). We made an experimental approach in the laboratory of civil engineering at the University of Laghouat (Algeria), in three reduced stepped channels models: model A (4cm x 7.5cm 4cmx) and model B (8cm x 7.5cm 8cmx), and the third model C size (12cm x 12 cm x 7.5 cm) developed "Plexiglas." In what follows, we set the rate of flow and vary the slope of the channel to show the effect of the slope on the energy dissipation. Three slopes were studied in this experiment:  = 15, 30 ° and  = 45 ° for the the model A, and  = 20 °, 30 ° and 45 ° for the the models B and C. The simulated flows range from 0.072 l/s to 2.569 l/s. As result, the effect of the rate flow allowed us to see that:  For low flows, the energy dissipation (nappe flow) is maximum is around 95% for the three models. For a large flow, the energy dissipation (nappe flow) is minimal and in the order of 82%, 80% and 77% for models A, B and C respectively;  The energy dissipation relative maximum and minimum flows in skimming flow are of the order of 73% and 70% respectively. 2. Physical model The experimental device consists of:  A flume made of Plexiglas length 5m, width 0.075 m, and height of the walls is 0.175 m (see photo 1);  A metal catchment connected to the glass by pipe carrying water pumped by a pump channel. This pipe has a valve for controlling the flow (see photo 1);  A channel model stairs made "Plexiglas." This pattern is connected to the glass channel seals, and mastic sealing installation;  A sump plastic for recycling the water to the supply conduit by PVC (gravity flow) basin, our system thus making a closed circuit. Experimental studies were conducted on three (03) models stairs developed "Plexiglas." The geometrical characteristics of the three models are shown in Table 1 The simulated flows range from 0.072 l/s to 2.569 l/s. 3. Analysis of results Comment In Figures 2 at 5, the experimental and analytical curves show the same profiles, that is, decreasing trends, of low (low value of the Froude number) at high flow rate (high value of the Froude number).  Energy dissipation in model A is greater than B and C models, and values as e.g. for α = 30 ° and Fr = 0.2: ∆H/H = 93.48 % (model A), ∆H/H = 86.79 % (mode B), ∆H/H = 81.41 % (model C);  For a given (Figures 2, 3 and 4) rate flow, the energy dissipation increases to a relative increase in the slope. This is explained by the increase in slope of the first channel which influences the increase in the height of the weir (Hchan= Lsinα), and therefore the increase of the kinetic energy for example model for C , for Fr = 0.1: ∆H/H=73.31 % for α=15°, ∆H/H=84.96 % for α=30° and ∆H/H = 89.66 % for α=45°;  For a given (Figures 2, 3 and 4) slope, the energy dissipation decreases with increased flow. This is explained by the effect of the increase of macro-roughness with increasing speed. Therefore the energy dissipation is reduced. For example for r model B (α = 45°) : Q = 0.167 l/s: ∆H/H = 93.726 %; Q = 0.586 l/s: ∆H/H = 90.630 %; Q = 0.820 l/s: ∆H/H = 89.544 %; Q = 1.995 l/s: ∆H/H = 85.224 %: 4. 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