Compound labyrinth weir is a new type of labyrinth weirs that consider a good applicable choice for increasing the capacity of discharge. The flow over a compound labyrinth weirs is a complex problem because the flow behavior is three-dimension. The present study aims to simulate the flow over the compound labyrinth weir into the critical regions that can not be observed when using an experimental test. The computational fluid dynamics (CFD) programme was utilised to implement a sensitive analysis for this purpose and different flow conditions. The MAPE and RMSE indices were utilised to verify the CFD results with experimental work. The statistics indices of the maximum error ME, RMSE and MAPE were 4.7%, 0.033 and 3.9 respectively. Therefore, the findings showed that there is a good matching between the experimental and CFD results. The CFD results demonstrated that the hydraulics behaviour of the compound labyrinth weir was similar to the oblique and linear weirs in high discharges. The results also confirmed that air cavities and bubbles existed behind the nappe flow in addition to the negative pressure that may occur beneath the nappe when the flow is aerated. Furthermore, the flow was divided into two parts and most streamlines were concentrated over the notches. Moreover, the flow velocity passing through the notches was bigger than the flow velocity over the high crest of the compound labyrinth weir.
Climate change has caused the inefficient operation of a significant number of old weirs to pass large discharges. Therefore, this study aims to increase the discharge capacity of the labyrinth weir. A new approach was proposed by modifying a labyrinth weir structure. The data were obtained from the quarter-round crest and different sidewall angles ranging from 8° to 35°. A conventional labyrinth weir was used for comparison. The results showed that the percentage of the notches area to sidewalls area of the weir (An/Aw) does not exceed 8%. Also, the percentage of the notches’ length to the total crest length (ΔL/Lc) does not exceed 32%. Also, the percentage of the notch depth to the sidewall depth (ΔP/P) does not exceed 30%. The other parameters are kept constant. These dimensionless terms provided a maximum compound discharge coefficient (Cdc) of 0.74. Also, the compound discharge coefficient initially increased at low water head ratios and decreased at higher values of water head ratios. The regression empirical equations were generated. A labyrinth weir with a larger sidewall angle was less efficient. The maximum increase in efficiency was 10% for a sidewall angle of 6° when compared to conventional labyrinth weirs.
Compound labyrinth weirs are a new shape that is used to increase discharge. The air pockets behind the nappe flow are a big problem for the hydraulic performance of the labyrinth weirs. The study aims to use the artificial ventilation approach to improve the performance of the compound labyrinth weirs. The current study proposes artificial ventilation techniques to mitigate the pressure behind nappe flow and to improve the coefficient of discharge. The data has been collected for three cases (without vented (WV), with vented (V), and with suction (S)). The results indicated that the pressure distribution behind nappe flow was not similar for all tested points. Also, a slight negative pressure was observed when H′t/P′ was measured between 0.1 and 0.2. Artificial ventilation with a suction pump was the best technique to reduce pressure behind the nappe flow when compared with a vent pipe device. Furthermore, the compound coefficient of discharge (Cdc) using the suction and vent devices was greater than the compound coefficient of discharge (Cdc) without the vent devices by 10% and 4.5%, respectively. The empirical equations were provided to predict the compound coefficient of discharge when pressure data behind nappe flow is available.
Labyrinth weirs are complex hydraulic structures. It has been widely used as a water regulator and to increase discharge in channels and spillway dams. The Labyrinth weirs are an economical and effective method to pass large floods. In addition, it is used to reduce the requirements of the structural footprint. These features make it an interesting and appropriate choice to increase the capacity of discharge. Several factors affect the discharge capacity and the hydraulic performance of the labyrinth weirs, including water level to crest height ratio, angle of sidewalls, apex width, conveyance channel conditions, and vertical aspect ratio. However, the present paper aims to summarise the most relevant knowledge of the hydraulic characteristics of the labyrinth weirs in the preceding articles. The importance of the present study is to provide a better understanding of how these weirs operate, in addition to which future studies deserve further investigation. The results demonstrated that some parameters still need further investigation. Also, energy dissipation over the labyrinth weir needs further investigation with different weir geometry. Furthermore, the results showed that common design equations did not take into account all parameters affecting labyrinth weir performance, including geometries, flow conditions, site conditions, and scale effect.
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