scholarly journals Effect of Corner Shape on Hydraulic Performance of One-Cycle Rectangular Labyrinth Weirs

Fluids ◽  
2020 ◽  
Vol 5 (3) ◽  
pp. 117
Author(s):  
Omed S. Q. Yousif ◽  
Moses Karakouzian
Keyword(s):  
Discharge Capacity ◽  
Hydraulic Performance ◽  
Acute Angle ◽  
Effective Length ◽  
Hydraulic Efficiency ◽  
Labyrinth Weir ◽  
Rounded Corner ◽  
Side Walls ◽  
The One ◽  
Labyrinth Weirs

The hydraulic performance of rectangular labyrinth weirs has been investigated by many researchers, however, the effects of the corner shape on the hydraulic performance of rectangular labyrinth weirs have not been addressed in the current literature. Accordingly, this experimental study aims to explore the effect of the corner shape of on discharge efficiency of rectangular labyrinth weirs. Five flat-crested rectangular labyrinth weirs, with five different corner shapes, were made of High-Density Polyethylene Plastic (HDPE) and tested in a rectangular flume. Under different overflow discharges, the discharge coefficients for the rectangular labyrinth weirs were determined. The results showed that the shape of corners for rectangular labyrinth weirs was an effective factor. For example, rounding or beveling the corners can significantly increase the discharge capacity of the rectangular labyrinth weirs. However, the rounded corner shape was slightly better than the beveled corner shape. Among all labyrinth weir models tested in this study, the rectangular labyrinth weir with a semi-circular apex showed the highest hydraulic efficiency, while the one with an acute-angle corner shape showed the lowest hydraulic efficiency. For the rectangular labyrinth weir having a semi-circular shape, although the original effective length reduced by about 14%, the discharge coefficient, CL, increased by 16.7% on average. For the rectangular labyrinth weir that has an acute-angle corner shape, although the effective length (LC) of the weir increased by 23%, its discharge capacity decreased by 35.2% on average. Accordingly, improper folding of the side-walls of the rectangular labyrinth weir led to a significant reduction in the weir’s hydraulic performance.

Performance of rectangular labyrinth weir- an experimental and numerical study

2022 ◽  
Author(s):  
Mosbah Ben Said ◽  
Ahmed Ouamane
Keyword(s):  
Discharge Capacity ◽  
Numerical Study ◽  
Flow Behavior ◽  
Rectangular Channel ◽  
Experimental Models ◽  
Absolute Relative Error ◽  
Labyrinth Weir ◽  
Specific Discharge ◽  
Labyrinth Weirs ◽  
Good Agreement

Abstract Labyrinth weirs are commonly used to increase the capacity of existing spillways and provide more efficient spillways for new dams due to their high specific discharge capacity compared to the linear weir. In the present study, experimental and numerical investigation was conducted to improve the rectangular labyrinth weir performance. In this context, four configurations were tested to evaluate the influence of the entrance shape and alveoli width on its discharge capacity. The experimental models, three models of rectangular labyrinth weir with rounded entrance and one with flat entrance, were tested in rectangular channel conditions for inlet width to outlet width ratios (a/b) equal to 0.67, 1 and 1.5. The results indicate that the rounded entrance increases the weir efficiency by up to 5%. A ratio a/b equal to 1.5 leads to an 8 and 18% increase in the discharge capacity compared to a/b ratio equal to 1 and 0.67, respectively. In addition, a numerical simulation was conducted using the opensource CFD OpenFOAM to analyze and provide more information about the flow behavior over the tested models. A comparison between the experimental and numerical discharge coefficient was performed and good agreement was found (Mean Absolute Relative Error of 4–6%).

Hydraulic Design of Inlet Guide Vane and its Full Flow Passage Numerical Simulation on Centrifugal Pump

2014 ◽  
Author(s):  
Hucan Hou ◽  
Yongxue Zhang ◽  
Zhenlin Li ◽  
Xin Zhou ◽  
Zizhe Wang
Keyword(s):  
Centrifugal Pump ◽  
Flow Rate ◽  
Guide Vane ◽  
Hydraulic Performance ◽  
Design Flow ◽  
Inlet Guide Vane ◽  
Hydraulic Efficiency ◽  
Flow Passage ◽  
Setting Angle ◽  
Hydraulic Design

In order to effectively improve hydraulic performance of centrifugal pump on off-conditions, the hydraulic design of inlet guide vane (IGV) was completed by adopting two dimensional theory in-house code based on one kind of IS series of centrifugal pump, which can achieve pre-whirl regulation of centrifugal pump. During design process the trailing edge of vane is assumed as equal velocity moment condition, and the distribution of vane setting angle along meridional streamline is also given as a quartic function firstly, the camber line is then drawn by point-by-point integration method and thickened at both sides along circumferential direction. With local vortex dynamics diagnosis theory, the optimal improvement of vane space shape can be finished by adjusting the design parameters of vane setting angle distribution coefficient ap. The full flow passage numerical simulations of centrifugal pump with IGV device are completed to analyze the influence of pre-whirl regulation on hydraulic performance of centrifugal pump under various pre-whirl angles. The results show that the pre-whirl regulation can improve the hydraulic performance of centrifugal pump on off-conditions. Under the positive pre-whirl regulation conditions, the best efficient point shift to small flow rate zone, and under the negative pre-whirl regulation conditions it moves to large flow rate zone. Compared with the pump without IGV device at the same flow rate condition of 0.8Q (Q the design flow rate), the hydraulic efficiency of centrifugal pump with IGV device improves obviously and reaches up to 1.43%. Meanwhile compared with that installed with the straight vanes designed based on the traditional theory, the inner flow field of centrifugal pump with the designed vanes improves and the overall hydraulic efficiency of centrifugal pump is somewhat increased.

scholarly journals Performance Advantages of Labyrinth Weir

2019 ◽  
Vol 9 (2S2) ◽  
pp. 26-29
Keyword(s):  
Control Flow ◽  
Water Bodies ◽  
Labyrinth Weir ◽  
Common Structure ◽  
Water Courses ◽  
Coefficient Of Discharge ◽  
Labyrinth Weirs

Weir is a very common structure across water courses to control flow and to release surplus water from water bodies. Simple straight weirs are less efficient compared to labyrinth weir where the weir length is increased by folds. In this research, experiments were conducted in the laboratory to find the increase in discharge due to labyrinth or decrease in coefficient of discharge due to labyrinth. Further two labyrinth weirs were analyzed to understand the efficiency with respect to the shape of the labyrinth weir. Compared to the ogee weir, the labyrinth weir discharges more water (more than 60%) for the same head of flow.

scholarly journals Prediction of Discharge Capacity of Labyrinth Weir with Gene Expression Programming

2020 ◽  
Author(s):  
Hossein Bonakdari ◽  
Isa Ebtehaj ◽  
Bahram Gharabaghi ◽  
Ali Sharifi ◽  
Amir Mosavi
Keyword(s):  
Gene Expression ◽  
Relative Error ◽  
Discharge Coefficient ◽  
Gene Expression Programming ◽  
Vertex Angle ◽  
Dimensionless Parameters ◽  
Labyrinth Weir ◽  
Predicted Values ◽  
Crest Length ◽  
Labyrinth Weirs

This paper proposes a model based on gene expression programming for predicting discharge coefficient of triangular labyrinth weirs. The parameters influencing discharge coefficient prediction were first examined and presented as crest height ratio to the head over the crest of the weir (p/y), crest length of water to channel width (L/W), crest length of water to the head over the crest of the weir (L/y), Froude number (F=V/√(gy)) and vertex angle () dimensionless parameters. Different models were then presented using sensitivity analysis in order to examine each of the dimensionless parameters presented in this study. In addition, an equation was presented through the use of nonlinear regression (NLR) for the purpose of comparison with GEP. The results of the studies conducted by using different statistical indexes indicated that GEP is more capable than NLR. This is to the extent that GEP predicts the discharge coefficient with an average relative error of approximately 2.5% in such a manner that the predicted values have less than 5% relative error in the worst model.

scholarly journals Energy Dissipation and Hydraulics of Flow over Trapezoidal–Triangular Labyrinth Weirs

Water ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1992 ◽  
Author(s):  
Amir Ghaderi ◽  
Rasoul Daneshfaraz ◽  
Mehdi Dasineh ◽  
Silvia Di Francesco
Keyword(s):  
Energy Dissipation ◽  
Discharge Coefficient ◽  
Residual Energy ◽  
Free Flow ◽  
Flow Conditions ◽  
Labyrinth Weir ◽  
Sidewall Angle ◽  
Weir Height ◽  
Downstream Flow ◽  
Labyrinth Weirs

In this work experimental and numerical investigations were carried out to study the influence of the geometric parameters of trapezoidal–triangular labyrinth weirs (TTLW) on the discharge coefficient, energy dissipation, and downstream flow regime, considering two different orientations in labyrinth weir position respective to the reservoir discharge channel. To simulate the free flow surface, the volume of fluid (VOF) method, and the Renormalization Group (RNG) k-ε model turbulence were adopted in the FLOW-3D software. The flow over the labyrinth weir (in both orientations) is simulated as a steady-state flow, and the discharge coefficient is validated with experimental data. The results highlighted that the numerical model shows proper coordination with experimental results and also the discharge coefficient decreases by decreasing the sidewall angle due to the collision of the falling jets for the high value of H/P (H: the hydraulic head, P: the weir height). Hydraulics of flow over TTLW has free flow conditions in low discharge and submerged flow conditions in high discharge. TTLW approximately dissipates the maximum amount of energy due to the collision of nappes in the upstream apexes and to the circulating flow in the pool generated behind the nappes; moreover, an increase in sidewall angle and weir height leads to reduced energy. The energy dissipation of TTLW is largest compared to vertical drop and has the least possible value of residual energy as flow increases.

Recent Changes in the Rain Regime in Israel 1975-2020

2021 ◽  
Author(s):  
Baruch Ziv ◽  
Ron Drori ◽  
Hadas Saaroni ◽  
Adi Etkin ◽  
Efrat Sheffer
Keyword(s):  
Rainy Season ◽  
Regional Climate ◽  
Daily Rainfall ◽  
The Other ◽  
Effective Length ◽  
Annual Rainfall ◽  
Rain Intensity ◽  
Subtropical Highs ◽  
The One ◽  
Mediterranean Oscillation

<p>Previous observation analyses have shown a declining rainfall trend over Israel, mostly statistically insignificant. These findings support the projections of the climatic models for the 21<sup>th</sup> century. The current study, for the period 1975-2020, undermines these findings, and the alarming future projections, and elaborates changes in the distribution of the rain along the rainy season.</p><p>The annual rainfall has a negligible trend, of +0.002%/decade, the number of rainy days has declined by -1.9%/decade and the average daily rainfall has increased by +2.1%/decade, all statistically insignificant. In the mid-winter both rainfall and daily rain intensity increased, while these variables have declined in the autumn and spring. The implied contraction of the rainy season is estimated by 2 measures. The 'effective length', which is determined by the time between accumulation of 10% and 90% of the annual rainfall, lasting 112 days on the average. This has been shortened by seven days during the study period. The other is the Seasonality Index (SI), reflecting the temporal concentration of the rainy season around its center. The trend found indicates that the regional climate is shifting from being between 'Markedly seasonal with a long dry season' and 'Most rain in ≤3 months', further toward the latter.</p><p>The trend in Cyprus Low occurrence and in the Mediterranean Oscillation Index were found to explain the rainfall trends only partially. We suggest that the cause for the increase in the mid-winter rain intensity is the increase in sea-surface temperature, found over the east Mediterranean, and for the decline in the transition seasons, to the poleward expansion of the subtropical highs. The contraction of the rainy season on the one hand, and the increased daily rain intensity in the mid-winter on the other, have ecological and hydrological impacts in this vulnerable region. </p>

Energy Method for the Calculation of High-Pier's Effective Length Factor at the Finished Stage

2013 ◽  
Vol 361-363 ◽  
pp. 1115-1118
Author(s):  
Peng Liu ◽  
Jie Rui ◽  
Bo Lei ◽  
Fei Zheng
Keyword(s):  
Boundary Conditions ◽  
Energy Method ◽  
Good Accuracy ◽  
Shape Function ◽  
Great Influence ◽  
Effective Length ◽  
Ideal Boundary ◽  
Effective Length Factor ◽  
High Pier ◽  
The One

This paper establishes the shape function of high-pier with non-ideal boundary conditions in the top and uses the energy method to calculate its critical load. Then its effective length factor is achieved by using Euler's formula. Further, the FEM and energy method are respect used to calculate the effective length factor of the engineering example and comparative analysis is carried on. Results show that: The non-ideal boundary conditions have great influence on the effective length factor and should be considered in the calculation. The result from the formula of energy method is nearly the same as the one from the FEM which demonstrates this method is of good accuracy to calculate the effective length factor of high-pier. In addition, it is also of great convenience in the design of high-piers.

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