TITLE:
Channel Slope Effect on Energy Dissipation of Flow over Broad Crested Weirs
AUTHORS:
Shaymaa A. M. Al-Hashimi, Huda M. Madhloom, Thameen N. Nahi, Nadhir Al-Ansari
KEYWORDS:
Broad Crested Weir, Numerical CFD Model, Standard k – ε Turbulence Model, Energy Dissipation Ratio (E%), Sloping Flume
JOURNAL NAME:
Engineering,
Vol.8 No.12,
December
9,
2016
ABSTRACT: The main purpose of broad crested weir used in open channels is to raise and control upstream (U/S) water level. In this study, a new performance was added to this weir, by making a step at downstream (D/S) of weir. The energy dissipation, the height of the weir/the upstream water height ratio and Froude number relationships (E% –P/h – Fr) for three range of flume slop S = 0.0, 0.002 and 0.004 were simulated. The experiments were performed in a laboratory horizontal channel of 4.6 m length, 0.3 m width and 0.3 m depth for a wide range of discharge. The D/S step height of the weir was 7.5 cm. FLUENT software was used as numerical model which represent a type of Computational Fluid Dynamics (CFD) model in order to simulate flow over weirs. The Volume of Fluid (VOF) method with the Standard k –ε turbulence model was used to estimate the free surface profile and the structured mesh with high concentration near the wall regions. The experimental results of the water surface profile gave a high agreement with the results of the numerical models. The maximum value 28.78 of E% was obtained in single step broad crested weir in the experimental result and 27.35 in numerical result at S = 0.004. Finally, the range of the relative error of the energy dissipation between experimental and numerical results was achieved and the maximum was 6.76 in all runs.