scholarly journals The Effect of Inception Point on Dissipation Energy in Stepped Spillways Modeling

2019 ◽  
Vol 54 (3) ◽  
Author(s):  
Denik Sri Krisnayanti ◽  
Suhardjono ◽  
Very Dermawan ◽  
Djoko Legono
Keyword(s):  
Energy Loss ◽  
Relative Energy ◽  
Downstream Face ◽  
Stepped Spillway ◽  
Critical Depth ◽  
Roughness Factor ◽  
Flow Conditions ◽  
Dissipation Energy ◽  
Stepped Spillways ◽  
Inception Point

Stepped spillway is generally a modification on the downstream face of a standard ogee spillway. The steps increase significantly the rate of energy dissipation taking place along the chute and reduce the size of the need for a large energy dissipate at the toe of the spillway. In skimming flow conditions, the steps act as roughness factor which is great because most of the energy is lost to maintain horizontal vortices that develop beneath the pseudo bottom. This study aimed to investigate the effect of the inception point against the value of the relative energy loss on the stepped spillway in skimming flow regime. In this research, the models test of stepped spillway carried out with twelve configuration and variations of ratio (dc/h). The slope of stepped spillway (θ) is used 30˚ and 45˚, the number of steps (N) are 40 and 20, and two type of steps: flat steps and pooled steps. The critical depth to the height of steps (dc/h) is ranging from 0.700 < dc/h < 3.00 with the discharge per unit width 69.13 cm2/s < q < 707.65 cm2/s. The results showed that the relative energy loss can be analyzed to be a function of the inception points, the number of steps, and the slope of spillway, in the equation form of (ΔH/Hmax) = a (Li/ks)bNc(sin θ)d. The discharge which function of the Froude number and height of the step already include to the length of inception point parameters.

FLOW AND ENERGY DISSIPATION OVER ON FLAT AND POOLED STEPPED SPILLWAY

2016 ◽  
Vol 78 (8) ◽  
Author(s):  
Denik Sri Krisnayanti ◽  
Soehardjono Soehardjono ◽  
Very Dermawan ◽  
Mohammad Sholichin
Keyword(s):  
Energy Dissipation ◽  
Energy Loss ◽  
Froude Number ◽  
Relative Energy ◽  
Stepped Spillway ◽  
Dissipation Energy ◽  
Stepped Spillways ◽  
Flow Energy ◽  
Physical Study ◽  
Roughness Elements

The stepped spillway has increasingly become effective energy dissipation. The stepped spillway has been accepted to be the most powerful hydraulic structure to dissipate large flow energy downstream from spillway crest. The steps act as roughness elements significantly increase the dissipation energy rate. The physical study has performed on flat and pooled stepped spillways with a slope spillway    (θ = 45˚) and number of steps (N): 20 and 40. The experiments were conducted for ten Froude number (Fr) run ranging from 1.117 to 9.909 with 0.700<yc/h<3.00. The focus of research to investigate the relationship between relative energy losses in skimming flow performance against Froude number on various stepped. The effect of number of steps is evident when the relative energy loss increases with the number of steps. In addition, the relative energy loss of flow on pooled steps is dissipating more energy than flat steps.

scholarly journals Genetic algorithms for optimizing stepped spillways to maximize energy dissipation

2021 ◽  
Author(s):  
Farzin Salmasi ◽  
John Abraham
Keyword(s):  
Water Management ◽  
Genetic Algorithm ◽  
Energy Dissipation ◽  
Objective Function ◽  
Relative Energy ◽  
Stepped Spillway ◽  
Construction Time ◽  
Stepped Spillways ◽  
Decision Variables ◽  
West Azerbaijan

Abstract Stepped spillways are important water-management structures that are used for energy dissipation. Use of these spillways has increased in recent decades, they can reduce construction time and they are effective for reducing the flow's downstream kinetic energy. In this study, the width and height of the steps as well as the slope and height of the overflow spillway were considered as variables. Due to the large number of variables, non-linearity of the objective function and constraints, and the lack of an explicit relationship between decision variables, a genetic algorithm (GA) was used. A stepped spillway with optimal dimensions was proposed as a replacement of the smooth spillway of Sarogh Dam located in West Azerbaijan province, Iran. The proposed steps increase energy dissipation; for constant discharge and varying slopes, the changes in the optimal height of the steps were insignificant. Sensitivity analysis using the objective function showed that the relative energy dissipation for a constant discharge is independent of the optimal height of the steps and decreases with increasing spillway slope. In addition, for fixed slopes, increasing the flow rate leads to a decrease in relative energy dissipation and an increase in the optimal height of the steps.

scholarly journals CFD Modelling of a Stepped Spillway with Various Step Layouts

2019 ◽  
Vol 2019 ◽  
pp. 1-11
Author(s):  
Shicheng Li ◽  
Qiulin Li ◽  
James Yang
Keyword(s):  
Kinetic Energy ◽  
Numerical Modelling ◽  
Energy Loss ◽  
Relative Energy ◽  
Secondary Flows ◽  
Stepped Spillway ◽  
Central Plane ◽  
Cfd Modelling ◽  
Flow Features ◽  
The Face

A traditional stepped spillway is prone to cavitation risks. To improve its hydraulic behaviors, distorted step faces and pool weirs are devised. By numerical modelling, comparative studies are conducted to look into the flow features. The pressures on step surfaces of the unconventional layouts exhibit 3D distributions. Pool weirs are essential in increasing both the min. and max. pressure loads. Pressures on the downstream bed show a unique pattern for V- and inverted V-shaped models, with the extreme pressures at the sidewalls for the former and at the central plane for the latter. Symmetrical secondary flows are formed in V- and inverted V-shaped cases with different patterns. Distributions of turbulent kinetic energy suggest differences in flow motions in all cases. Furthermore, the relative energy loss of flat setups is ∼5.4% lower than that of the pooled ones with the same step face angle; inverting the face angle does not give rise to noticeable change. The results provide reference for relevant projects.

scholarly journals Stepped Spillway Slope Effect on Air Entrainment and Inception Point Location

Water ◽  
2021 ◽  
Vol 13 (10) ◽  
pp. 1428
Author(s):  
Awais Raza ◽  
Wuyi Wan ◽  
Kashif Mehmood
Keyword(s):  
Air Entrainment ◽  
Stepped Spillway ◽  
Point Location ◽  
Step Size ◽  
Zone Length ◽  
Flow Rates ◽  
Stepped Spillways ◽  
Flow Surface ◽  
Channel Slope ◽  
Inception Point

Spillway is a crucial hydraulic structure used to discharge excess water from the dam reservoir. Air entrainment is essential to prevent cavitation damage on the spillway, however, without air entrainment the risk of cavitation over the spillway increases. The most important parameter for the determination of air entrainment in stepped spillways is the inception point. The inception point is the location where the air starts to inter into the water flow surface over the spillway. It occurs when the turbulent boundary layer meets the free surface. The location of the inception point depends upon different parameters like flow rate, geometry, step size, and slope of the spillway. The main aim of this study was applying numerical simulation by using the realizable k-ϵ model and the volume of fluid (VOF) method to locate the location of the inception point. For this purpose, by using different stepped spillways with four different slopes (12.5°, 19°, 29°, and 35°) different flow rates were simulated, which gives the location of the inception point of different channel slopes of stepped spillways at different flow rates. The results demonstrated that the inception point location of mild slopes is farther from the crest of the spillway than the steep slope stepped spillway. Non-aerated flow zone length increases when the channel slope decreases from steep to mild slope.

scholarly journals Flow Simulation and Energy Loss Estimation in the Nappe Flow Regime of Stepped Spillways with Inclined Steps and End Sill: A Numerical Approach

2016 ◽  
Vol 2 (9) ◽  
pp. 426-437 ◽  
Author(s):  
Amirmasoud Hamedi ◽  
Mohammad Hajigholizadeh ◽  
Abbas Mansoori
Keyword(s):  
Numerical Simulation ◽  
Energy Loss ◽  
Flow Pattern ◽  
Flow Direction ◽  
Low Cost ◽  
Flow Simulation ◽  
Numerical Approach ◽  
Stepped Spillway ◽  
Stepped Spillways ◽  
Time Required

Recently, the usage of stepped spillways, as energy dissipaters, has increased and led to a reduction in the size of the stilling basin. Extensive experimental considerations, plus the high cost and extended time required for laboratory methods, are among the major issues that require precise attention to determine optimal step design. This research deals with comparing the 2-D numerical simulation and experimental description in stepped spillways equipped with inclined steps and end sill together and presents a brisk, reliable, low-cost, and non-experimental approach to designing the steps. In this new type and complicated geometry, simulation is more complicated than horizontal steps, because it needs more accuracy around the end sills. The VOF Method and the k-ε standard turbulence model are proposed to simulate the flow pattern and evaluate the energy loss over stepped spillway. Energy dissipations obtained through the numerical approach have been compared with laboratory measurements and demonstrate reasonable agreement. Also, the flow pattern, velocity vectors and flow direction resulted from numerical simulation is in a good agreement with the experimental results.

scholarly journals Numerical Study on the Hydraulic Properties of Flow over Different Pooled Stepped Spillways

Water ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 710
Author(s):  
Amir Ghaderi ◽  
Saeed Abbasi ◽  
Silvia Di Francesco
Keyword(s):  
Energy Dissipation ◽  
Numerical Study ◽  
Air Entrainment ◽  
Computational Procedure ◽  
Maximum Pressure ◽  
Stepped Spillway ◽  
Stepped Spillways ◽  
Pressure Distributions ◽  
Efficiency Performance ◽  
Inception Point

This work presents numerical simulations carried out to study the influence of geometric characteristics of pooled steps on the energy dissipation performance, flow patterns properties, velocity rates, and pressure distributions over a spillway. The localization of the inception point of air entrainment was also assessed, being a key design parameter of spillways. With this aim, different configurations of steps were taken in account, including flat, pooled, and notch pooled types. The computational procedure was first validated with experimental results from the literature and then used to test the hydraulic behavior derived from different geometric configurations. The flat step configuration showed the best energy dissipation performance as compared with other configurations. With the notched pooled step configuration, the efficiency performance of the pooled structure improved by about 5.8%. The interfacial velocities of the flat stepped spillway were smaller than those of the pooled structure. The pressure value at the beginning of the step in the pooled configuration was larger than the flat configuration, while for the notched pool the maximum pressure values decreased near the step pool. Pool configuration (simple or notched) did not have a significant influence on the location of air entrainment.

scholarly journals Induced aeration flow over stepped spillways: mean pressures, air entrainment and flow behavior

RBRH ◽  
2021 ◽  
Vol 26 ◽  
Author(s):  
Carolina K. Novakoski ◽  
Rute Ferla ◽  
Priscila dos Santos Priebe ◽  
Aline Saupe Abreu ◽  
Marcelo G. Marques ◽  
...  
Keyword(s):  
Flow Behavior ◽  
Air Entrainment ◽  
Stepped Spillway ◽  
Air Concentration ◽  
Stepped Spillways ◽  
Jet Impact ◽  
Entrainment Coefficient ◽  
The Mean ◽  
Inception Point ◽  
Channel Bottom

ABSTRACT Stepped spillways can dissipate a great amount of energy during the flow passage over the chute, however these structures have limited operation due to the risk of cavitation damage. The induced aeration may protect the concrete chute through the air concentration near the channel bottom. Furthermore, some research studies have indicated that the presence of air in flows may reduce the mean pressures. The present research aims to analyze mean pressures, air entrainment coefficient and flow behavior over a stepped spillway with aeration induced by two different deflectors, comparing the results to natural aeration flow. Despite the jet impact influence, the induced aeration does not change significantly the mean pressures compared to natural aeration flow. The air entrainment coefficient, as well as the jet impact position, is higher for the deflector with the longer extension and, although air bubbles can be seen throughout the extension of the chute due to the air entrainment through the inferior flow surface, the induced aeration did not anticipate the boundary layer inception point position.

scholarly journals Effect of Height and Geometry of Stepped Spillway on Inception Point Location

2019 ◽  
Vol 9 (10) ◽  
pp. 2091 ◽  
Author(s):  
Wuyi Wan ◽  
Awais Raza ◽  
Xiaoyi Chen
Keyword(s):  
Air Entrainment ◽  
Step Height ◽  
Stepped Spillway ◽  
Point Location ◽  
Flow Zone ◽  
Cavitation Damage ◽  
Stepped Spillways ◽  
Aerated Flow ◽  
Inception Point ◽  
Step Number

Air entrainment in a stepped spillway is very important to protect the spillway from cavitation damage. The inception point is the location where air starts entering the non-aerated flow zone. The inception point location depends on different parameters, such as the discharge, step height, and step shape. In this paper, various stepped spillways, including flat steps, pooled steps, and round steps with different step heights were numerically simulated using the volume of fluid and realizable k-ε models. The results indicate that the inception point location moves downwards with the increase of the discharge of the stepped spillways. The length of the non-aerated flow zone increases with the discharge. The inception point location moves downwards as the step height decreases and the step number increases at the same discharge. The inception point location of the round stepped spillway model is much closer to the spillway crest than that of the flat stepped spillway with the same number of steps. The inception point location of the pooled stepped spillway is closer to the spillway crest than that of the flat stepped spillway, but more downstream than that of the round stepped spillway.

scholarly journals Numerical study of energy dissipation and block barriers in stepped spillways

2020 ◽  
Author(s):  
Mehdi Karami Moghadam ◽  
Ata Amini ◽  
Ehsan Karami Moghadam
Keyword(s):  
Energy Dissipation ◽  
Numerical Study ◽  
Flow Simulation ◽  
Step Length ◽  
Energy Dissipation Rate ◽  
Relative Energy ◽  
Stepped Spillway ◽  
Stepped Spillways ◽  
Using Data ◽  
Turbulent Models

Abstract In this research, the accuracy of the Flow-3D numerical model in the flow simulation in a stepped spillway was probed using data obtained from the physical model. In addition, the effects of block barriers on the energy dissipation rate were investigated. To adopt a proper turbulent model, Renormalization Group k-ε, RNG k-ε, and standard k-ε models were employed. Then, the Flow-3D was run in five discharges for nine spillways with the ratios of block length to step length (Lb/l) and block height to step height (Hb/h) as 0.3, 0.4, and 0.5. The results indicated that both turbulent models had almost similar outcomes though the run time of the RNG k-ε model was shorter. The blocks with a shorter length in low ratios of Hb/h and the lengthier blocks in high ratios of Hb/h undergo more relative energy dissipation relative to the no-block situation. For Hb/h = 0.3 and Lb/l equal to 0.3, 0.4, and 0.5, the relative energy dissipation climbed on average as 8.5, 6.5, and 4.5% respectively, compared with the no-block case. The most influence exerted on relative energy dissipation was obtained via the blocks with Hb/h = Lb/l equal to 0.3 and 0.5 with respective increases of 8.6 and 8.4%.

scholarly journals Numerical Study to Evaluate the Performance of Nonuniform Stepped Spillway Using ANSYS-CFX

2020 ◽  
Vol 10 (2) ◽  
pp. 1-9
Author(s):  
Shawnm M. Saleh ◽  
Sarhang M. Husain
Keyword(s):  
Energy Dissipation ◽  
Numerical Study ◽  
Energy Dissipation Rate ◽  
Step Height ◽  
Stepped Spillway ◽  
Stepped Spillways ◽  
Flow Discharge ◽  
Flow Energy ◽  
Ansys Cfx ◽  
Inception Point

The main features that attract hydraulic engineers for designing stepped spillways are their ability to lose a large portion of the flow energy and add or increase aeration to the flow naturally. Hence, smaller size stilling basin and no aeration device may require. This study aims to find the amount of energy dissipation rate and the location of inception point over non-uniform stepped spillway. The numerical 2D ANSYS-CFX code is applied to generate and run thirty-two models of different configurations using two different moderate slopes (1 V:2 H and 1 V:2.5 H) as most of the downstream slopes designed for moderate slope, and two different step heights (hs= 0.08 m and hs= 0.016 m) under skimming flow discharge for different (dc/hs) ranging from dc/hs= 1–2.2, in which dc is the critical flow deptho n the crest. The volume of fluid is implemented and the renormalized group of k-ɛ turbulence model is activated. The computational results demonstrated that the amount of energy dissipation increases with decreasing the flow discharge, chute slope, and step height. In addition, it is observed that the length of the inception point is directly proportional to the discharge and inversely proportional to both the chute slopes and step height. Moreover, for the design point of view, the results revealed that configuration B can be considered as the optimal one amongst the others examined herein.

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