Experimental investigation of flow energy dissipation in sinusoidal trapezoidal labyrinth weirs

Document Type : Original Research

Authors
S. nematolahi 1
E. Izadinia 2
A. Khoshfetrat 3
E. Delavari 4
1 Department of Civil Engineering, Islamic Azad University, Najafabad Branch, Isfahan, Iran
2 Assistant Professor, Department of Civil Engineering, Shahid Ashrafi Esfahani University, Isfahan, Iran
3 Assistant Professor, Water Studies Research Center, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran
4 Assistant Professor, Faculty of Civil Engineering, Najafabad Branch, Islamic Azad University, Najafabad, Iran.
10.22034/24.4.95
Abstract
Labyrinth weirs are of the non-linear weirs whose discharge coefficient is higher than similar linear weirs. These weirs have a simple structure. They are mainly made in rectangular, trapezoidal, triangular and semicircular shapes. Investigating the amount of energy loss in these high-efficiency weirs has become very important for engineers in recent years. The experiments were carried out in a flume with a length of 10 meters, a width of 0.6 meters and a height of 0.8 meters. The flow is fed by a pump with an error of 0.01% by three surface tanks and after passing through the flow relaxers into the flume. In this research, four sinusoidal labyrinth weirs were used to check the amount of energy loss. The first spillway has a crown length of 1.3 meters, the second spillway has a crown length of 1.5 meters, the third spillway has a crown length of 1.55 meters, and the fourth spillway has a crown length of 1.6 meters. Also, the first and second weirs have a height of 0.15 meters and the width ratio of the inlet to the outlet is 6.86, and the third and fourth weirs have a height of 0.18 meters and the width ratio of the inlet to the outlet is 7.67. The flow depth in the upstream and downstream of the weir was taken by a point gauge with an error of 1 mm. Weirs are installed at a distance of 5.5 meters from the beginning of the channel. The downstream depth of the spillway was not artificially adjusted by the end valve of the laboratory flume. The weirs are made of wood and wood glue was used for their impermeability. The flow is transferred downstream over the sinusoidal edges of the weir like a curved slide or similar to peak weirs. Also, due to the sinusoidal nature of the weirs, the flow will be transferred downstream faster next to the walls. At the edge of the keys, a local vacuum is created. As the flow rate increases, the available air volume increases. At the downstream of the inlet and outlet keys, a vortex and rotation of the flow is formed, which increases in strength as the flow speed increases. The reason for the formation of vortices is the interference of the falling flow from each sinus. Due to the sinusoidal nature of the flow and the indentations and protrusions in the weir, the flow enters the downstream with a curve and the outflow from each sinus is mixed with the outflow from the other sinus. Also, at the beginning of the outlet keys, a small submerged area is formed, which increases in length and moves downstream as the flow rate increases. In front of the inlet keys, two relatively strong hydraulic jumps are formed, and after that the flow is transferred downstream more calmly. The results were that by increasing the flow rate or increasing the depth of the flow upstream of the weir, the energy loss decreased. Also, the amount of energy loss increases with the effective length of weirs. By increasing the ratio of the width of the input keys to the width of the weir output keys, the amount of energy loss increases. Also, by increasing the ratio of flow depth plus height, such as kinetic energy upstream of the weir to the height of the weir, the amount of energy loss decreases. The amount of energy loss is the highest in the fourth weir and the third weir, respectively. On average, with a 20% increase in the height of the weir, the amount of energy loss increases by 23.2%. Also, the average energy loss in type A, B, C, and D weirs is 42.3, 47.2, 57.9, and 58.6, respectively.

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Modares Civil Engineering journal
Volume 24, Issue 4
September and October 2024
Pages 95-102