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 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 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 Numerical Analysis of Pressure Profiles and Energy Dissipation across Stepped Spillways Having Curved Risers

2022 ◽  
Vol 12 (1) ◽  
pp. 448
Author(s):  
Najam us Saqib ◽  
Muhammad Akbar ◽  
Huali Pan ◽  
Guoqiang Ou ◽  
Muhammad Mohsin ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Stokes Equations ◽  
Free Surface Flow ◽  
Air Entrainment ◽  
Surface Flow ◽  
Stepped Spillway ◽  
Flow Rates ◽  
Stepped Spillways ◽  
Pressure Profiles ◽  
Negative Pressures

In this study, curved risers stepped spillways models based on the increasing angle of suspension were tested to check for improvement in energy dissipation and pressure distributions. Four fourteen-steps stepped spillway models with a slope 1:0.84 were selected, using Froude’s number non-dimensional similarity. The risers of steps were made curved, based on three angles of suspensions, i.e., 30°, 60°, and 90°. The simulations were performed by FLOW 3D software and by the turbulence model Renormalization Group (RNG) for discharges between 0.020 and 0.068 m3/s followed by the model calibration. The 3D Reynolds-averaged Navier–Stokes equations were solved, which included sub-grid models for air entrainment, density evaluation, and drift–flux, to capture free-surface flow over the stepped spillway. It was estimated that curving the risers increases the energy dissipation up to three percent for lower flow rates, whereas it has no significant impact on energy dissipation for higher flow rates. It was found that in simply stepped spillway lower steps dissipate more energy as compared to curved risers stepped where energy dissipation is shifted to higher steps. On the other hand, curved risers stepped spillways showed lower values of negative pressures as compared to the simply stepped spillway. It was seen that a higher energy dissipating step as experienced more negative pressures as compared to the lower energy dissipating step.

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 Numerical investigation of flow characteristics over stepped spillways

2020 ◽  
Author(s):  
Aytaç Güven ◽  
Ahmed Hussein Mahmood
Keyword(s):  
Numerical Model ◽  
Turbulent Flow ◽  
Flow Characteristics ◽  
Air Entrainment ◽  
Stepped Spillway ◽  
Stepped Spillways ◽  
Entrainment Velocity ◽  
Fluid Flow Characteristics ◽  
3D Package ◽  
Good Agreement

Abstract Spillways are constructed to evacuate the flood discharge safely not to let the flood wave overtop the dam body. There are different types of spillways, ogee type being the conventional one. Stepped spillway is an example of nonconventional spillways. The turbulent flow over stepped spillway was studied numerically by using the Flow-3D package. Different fluid flow characteristics such as longitudinal flow velocity, temperature distribution, density and chemical concentration can be well simulated by Flow-3D. In this study, the influence of slope changes on flow characteristics such as air entrainment, velocity distribution and dynamic pressures distribution over the stepped spillway was modelled by Flow-3D. The results from the numerical model were compared with the experimental study done by others in the literature. Two models of the stepped spillway with different discharge for each model was simulated. The turbulent flow in the experimental model was simulated by the Renormalized Group (RNG) turbulence scheme in the numerical model. A good agreement was achieved between the numerical results and the observed ones, which were exhibited in terms of graphics and statistical tables.

scholarly journals Computational Study to Predict the Free-Surface Flow over Non-uniform Stepped Spillway Using ANSYS-CFX

2020 ◽  
Vol 10 (1) ◽  
pp. 43-50
Author(s):  
Shawnm M. Saleh ◽  
Sarhang M. Husain
Keyword(s):  
Free Surface ◽  
Computational Study ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Stepped Spillway ◽  
Step Size ◽  
Stepped Spillways ◽  
Ansys Cfx ◽  
Long Time ◽  
Stepped Cascade

Using stepped chutes as a structure for controlling flood discharges is applicable for long time. Measuring the depth of flow over that structure is essential for designing of the side walls. The aim of this paper is to determine the free-surface that flows on spillway equipped with non-uniform step sizes. For that purpose, the two-dimensional software package code of ANSYS-CFX has been utilized to run eight configurations of two moderate slopes (1V:2H and 1V:2.5H) and for four different discharges 1≤dc/hs≤2.2 to determine the effect of flow discharges, chute slopes, and step heights on the position of free surface along the structure over non-uniform stepped cascade. The hexahedral grid size of 0.015 m is selected with inflation technique close to the walls. In addition, the renormalized group of k-ε (RNG) turbulence model is implemented and the numerical volume of fluid software is employed. The results show smoother stream for higher discharges, and the free-surface drops when the slope of chutes increases. Moreover, it is found that the step size has insignificant effect on the depth of water. The results of this study are important because they provide new insight in improving the design of stepped spillways. It is recommended to perform more investigations to evaluate their effectiveness in other flow parameters including pressure distribution and energy dissipation rates.

scholarly journals NUMERICAL STUDY OF TURBULENT FLOW FOR MODERATE-SLOPE STEPPED SPILLWAYS

2018 ◽  
Vol 30 (1) ◽  
Author(s):  
Bentalha Chakib
Keyword(s):  
Hydraulic Structure ◽  
Numerical Study ◽  
Air Entrainment ◽  
Work Flow ◽  
Stepped Spillway ◽  
Cavitation Damage ◽  
Stepped Spillways ◽  
Vof Model ◽  
Computational Fluid Dynamics Cfd ◽  
Stepped Chute

Stepped spillway is a power full hydraulic structure for energy dissipation because ofthe large value of the surface roughness. The performance of the stepped spillway is enhancedwith the presence of air that can prevent or reduce the cavitation damage. This work aims tosimulate air entrainment and determine the characteristics of flow at stepped spillways. Withinthis work flow over stepped chute is simulated by using fluent computational fluid dynamics(CFD). The volume of fluid (VOF) model is used as a tool to simulate air-water interaction onthe free surface thereby the turbulence closure is derived in the k −ε turbulence standard model.The found numerical results agree well with experimental results.

scholarly journals Free surface profile and inception point as characteristics of aerated flow over stepped spillway: Numerical study

2019 ◽  
Vol 42 (1) ◽  
pp. 42-48
Author(s):  
Chakib Bentalha ◽  
Mohammed Habi
Keyword(s):  
Free Surface ◽  
Kinetic Energy ◽  
Water Depth ◽  
Numerical Study ◽  
Surface Profile ◽  
Air Entrainment ◽  
Stepped Spillway ◽  
Ansys Fluent ◽  
Vof Model ◽  
Inception Point

Abstract Stepped spillway is hydraulic structure designed to dissipate the excess in kinetic energy at the downstream of dams and can reduce the size of stilling basin at the toe of the spillway or chute. The flow on a stepped spillway is characterised by the large aeration that can prevent or reduce the cavitation damage. The air entrainment starts where the boundary layer attains the free surface of flow; this point is called “point of inception”. Within this work the inception point is determined by using software Ansys Fluent where the volume of fluid (VOF) model is used as a tool to track the free surface thereby the turbulence closure is derived in the k − ε turbulence standard model. This research aims to find new formulas for describe the variation of water depth at step edge and the positions of the inception point, at the same time the contour map of velocity, turbulent kinetic energy and strain rate are presented. The found numerical results agree well with experimental results like the values of computed and measured water depth at the inception point and the numerical and experimental inception point locations. Also, the dimensionless water depth profile obtained by numerical method agrees well with that of measurement. This study confirmed that the Ansys Fluent is a robust software for simulating air entrainment and exploring more characteristics of flow over stepped spillways.

scholarly journals Predicting the Flow Velocity at the Toe of a Labyrinth Stepped Spillway

2021 ◽  
Vol 18 (1) ◽  
pp. 20-25
Author(s):  
Jaafar S. Maatooq
Keyword(s):  
Kinetic Energy ◽  
Flow Velocity ◽  
Smooth Surface ◽  
Air Entrainment ◽  
Physical Models ◽  
Stepped Spillway ◽  
Stepped Spillways ◽  
Stilling Basin ◽  
Major Variable ◽  
Jet Velocities

The velocity at the toe of a spillway is a major variable when designing a stilling basin. Reducing this velocity leads to reduce the size of the basin as well as the required appurtenances which needs for dissipating the surplus kinetic energy of the flow. If the spillway chute is able to dissipate more kinetic energy, then the resulting flow velocity at the toe of spillway will be reduced. Typically, stepped spillway is able to dissipate more kinetic energy than that of a smooth surface. In the present study, the typical uniform shape of the steps has been modified to a labyrinth shape. It is postulated that a labyrinth shape can increase the dissipation of kinetic energy through increasing the overlap between the forests of nappe will circulating the flow that in turns leading to further turbulence. This action can reduce the jet velocities near the surfaces, thus minimizing cavitation. At the same time the increasing of circulation regions will maximize the opportunity for air entrainment which also helps to dissipate more kinetic energy. The undertaken physical models were consisted of three labyrinth stepped spillways with magnification ratios (width of labyrinth to width of conventional step) WL/W are 1.1, 1.2, and 1.3 as well as testing a conventional stepped spillway (WL/W=1). It is concluded that the spillway chute coefficient is directly proportional to the labyrinth ratio and its value decreases as this ratio increases.

scholarly journals Experimental investigation on effective scouring parameters downstream from stepped spillways

2020 ◽  
Vol 20 (5) ◽  
pp. 1988-1998 ◽  
Author(s):  
Amir Ghaderi ◽  
Rasoul Daneshfaraz ◽  
Mohammadamin Torabi ◽  
John Abraham ◽  
Hazi Mohammad Azamathulla
Keyword(s):  
Flow Regime ◽  
Cross Section ◽  
Experimental Tests ◽  
Mean Square ◽  
Step Size ◽  
Flow Rates ◽  
Stepped Spillways ◽  
Scouring Depth ◽  
Scour Hole Dimensions ◽  
Hole Dimensions

Abstract Experimental tests were carried out to investigate the effective scouring parameters downstream from stepped spillways with different flow rates and step sizes. The results indicated that the flow regime plays an important role in scour-hole dimensions such that the minimum scouring depth happens in the nappe flow regime. Moreover, step size and tailwater depth are essential parameters for maximum scouring depth. Increasing tailwater depth from 6.31 cm to 8.54 cm and then to 11.82 cm decreases the scouring depth by 18.56% and 11.42%, respectively. These alterations also decrease the scouring length by 31.43% and 16.55%, respectively. By increasing the flow rate, the particle Froude number will increase, and the increased momentum of the flow promotes scouring. In addition, the results show that scouring at the sidewalls is higher than in the middle of the cross-section. Finally, an empirical formula with root mean square error = 0.107 and R2 = 0.974 is proposed to predict the maximum scouring depth downstream from the stepped spillways. Comparisons were made between the proposed formula and experimental results. This comparison demonstrated that the formula can predict souring depth to within 3.86% and 9.31% relative and maximum errors, respectively.

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