Simulation of local scour development downstream of broad-crested weir with inclined apron

Year 2017, Issue: Özel Sayı - Special Issue, 57 - 61, 31.12.2017

Arkan Ibrahım Azheen Karım Mustafa Günal

Abstract

Broad crested weirs are hydraulic structures used to control the flow depth and discharge of channels. Structures constructed in rivers
and channels are exposed to scour around their foundations as they cause turbulences in uniform flow and sediment transport as a
result of increase in flow velocities at downstream. If the scour depth becomes substantial the stability of the foundations endangered
with a resultant hazard to the structural failure. In this study the flow field variation and the equivalent depth of scour was simulated
by means of three-dimensional numerical analysis using a sediment scour model of FLOW-3D program. The sediment scour model in
FLOW-3D is able to simulate the scour hole development process, in this study four models of inclined apron of broad crested weirs
[A, B, C, D] with different downstream reverse angles (0°
, 4.5°
, 8.7°
,13°
) respectively are tested under the same flow intensity and the
same duration, based on experimental study from the literature that has been held for a duration of 6 hours to see if the same behavior
will be concluded for scour reduction. Downstream of the first models act as ordinary weir while the other models act as an obstacle
toward the flow, the water flows above the sloped downstream bed and dissipates some of its energy. There was a good agreement
between experimental and FLOW-3D results. The results showed, that model C reduces local scour hole volume, the maximum scour
depth in addition shift the scour holes away from the structure as compared to the other models. The idea is decreasing downstream
height of broad crested weir while providing an obstacle in shape of sloped downstream bed toward the flowing water. This reduction
gave the weir a new performance by making it as an energy dissipater. The present technique similarly reduces construction costs also
improves the hydraulic performance of single step broad crested weirs. 

Keywords

Sediment scour, scour reduction, erosion, FLOW-3D, broad crested weir

Supporting Institution

TUBITAK

Project Number

111Y319

Thanks

The authors are grateful to Ministry of Environment and Urbanism of Turkey for the air quality data. This work was part of the Turkish Scientific and Technical Research Council (TUBITAK) Project No: 111Y319. This study is a background of the online integrated air quality and meteorology modeling project funding by the TUBITAK and COST Action ES1004.

Simulation of local scour development downstream of broad-crested weir with inclined apron

Abstract

Broad crested weirs
are hydraulic structures used to control the flow depth and discharge of
channels. Structures constructed in rivers and channels are exposed to scour
around their foundations as they cause turbulences in uniform flow and sediment
transport as a result of increase in flow velocities at downstream. If the
scour depth becomes substantial the stability of the foundations endangered
with a resultant hazard to the structural failure. In this study the flow field
variation and the equivalent depth of scour was simulated by means of
three-dimensional numerical analysis using a sediment scour model of FLOW-3D
program. The sediment scour model in FLOW-3D is able to simulate the scour hole
development process, in this study four models of inclined apron of
broad crested weirs [A, B, C, D] with different
downstream reverse angles
(0^°, 4.5^°, 8.7^° ,13^°) respectively are tested under the
same flow intensity and the same duration, based on experimental study from the
literature that has been held for a duration of 6 hours to see if the same
behavior will be concluded for scour reduction. Downstream of the first models
act as ordinary weir while the other models act as an obstacle toward the flow,
the water flows above the sloped downstream bed and dissipates some of its
energy. There was a good agreement between experimental and FLOW-3D results.
The results showed, that model C reduces local scour hole volume, the maximum
scour depth in addition shift the scour holes away from the structure as
compared to the other models. The idea is decreasing downstream height of broad
crested weir while providing an obstacle in shape of sloped downstream bed
toward the flowing water. This reduction gave the weir a new performance by
making it as an energy dissipater. The present technique similarly reduces
construction costs also improves the hydraulic performance of single step broad
crested weirs.

Keywords

Sediment scour, scour reduction, erosion, FLOW-3D, broad crested weir

Project Number

111Y319

References

• Abdulnaser A., Mustafa G., Hamid H. 2015. Investigating of Local Scour and Discharge Characteristics of Single Step Broad Crested Weir. (ICCESEN 2015), 14-19 October, 2015. Antalya-Turkey.
• Abdelhaleem F.S.F. 2013. Effect of semi-circular baffle blocks on local scour downstream clear-overfall weirs. Ain Shams Eng J 4 (4) 675–684.
• Amin A.M.A. 2015. Physical model study for mitigating local scour downstream of clear over-fall weirs, Ain Shams Eng J 6 (4) 1143-1150.
• Brethour, J. 2003. Modeling Sediment Scour. Flow Science, Inc. Report FSI-03-TN62.
• Dargahi B. 2003. Scour development downstream of a spillway. J Hydraul Res; 41(4):417–426.
• Flow Science Inc. 2009. Flow-3D v9.3. New Mexico, USA.
• King, H.W. and E.F. Braver 1963. Handbook of Hydraulics, 5th Edition, McGraw-Hill Book Company, New York.
• Helal E.Y. 2013. Minimizing scour downstream of hydraulic structures using single line of floor water jets Ain Shams Eng J. 5(1) 17-28.
• Ozmen-Cagatay H. and Kocaman S. 2011. Dam-break flow in the presence of obstacle: experiment and CFD simulation. Engineering Applications of Computational Fluid Mechanics 5(4) 541-552.