scholarly journals Stepped spillway with pre-aeration by a deflector: flow characteristics

RBRH ◽  
2020 ◽  
Vol 25 ◽  
Author(s):  
Carolina Kuhn Novakoski ◽  
Rute Ferla ◽  
Maurício Dai Prá ◽  
Alba Valéria Brandão Canellas ◽  
Marcelo Giulian Marques ◽  
...  
Keyword(s):  
Flow Characteristics ◽  
Air Entrainment ◽  
Stepped Spillway ◽  
Cavitation Damage ◽  
Flow Passage ◽  
Stepped Spillways ◽  
Air Supply ◽  
Stepped Chute ◽  
Airtight Chamber ◽  
Reduced Scale

ABSTRACT Stepped spillways aim to dissipate part of the upstream energy during the flow passage by the chute. However, the use of these structures is limited to a restrict range of specific discharges due to the risk of cavitation damage. As the air entrainment into the flow assists the concrete protection against the aforementioned damages, a possible solution by aerators installed along the chute, already disseminated to smooth chutes, is being studied to be used also in stepped spillways. The purpose of the present paper is to characterize a flow over a stepped chute with induced aeration by deflector and air supply by an airtight chamber trough tests conducted on a reduced scale physical model. The main regions observed during the tests are presented and were developed four equations that allow to approximately predict the location of the main regions for a given spillway.

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 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 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 Stepped spillway flows and air entrainment

1993 ◽  
Vol 20 (3) ◽  
pp. 422-435 ◽  
Author(s):  
Hubert Chanson
Keyword(s):  
Energy Dissipation ◽  
Flow Characteristics ◽  
Air Entrainment ◽  
Stepped Spillway ◽  
Calculation Methods ◽  
Stepped Spillways ◽  
Popular Method ◽  
Roller Compacted Concrete ◽  
Construction Techniques ◽  
Recent Developments

Stepped spillways have become a popular method for handling flood releases. The steps significantly increase the rate of energy dissipation taking place on the spillway face and reduce the size of the required downstream energy dissipation basin. The compatibility of stepped spillways with roller compacted concrete and gabion construction techniques results in low additional cost for the spillway. This paper presents a review of recent developments for the design of stepped spillways, provides a discussion of the effects of air entrainment, and presents new calculation methods that take into account the effects of flow aeration on the flow characteristics and the rate of energy dissipation. Key words: stepped spillway, air entrainment, dam, spillway, energy dissipation.

scholarly journals Experimental investigations of air entrainment in transition and skimming flows down a stepped chute

2002 ◽  
Vol 29 (1) ◽  
pp. 145-156 ◽  
Author(s):  
H Chanson ◽  
L Toombes
Keyword(s):  
Free Surface ◽  
Water Flow ◽  
Air Entrainment ◽  
Stepped Spillway ◽  
Transition Flow ◽  
Flow Properties ◽  
Flow Measurements ◽  
Surface Aeration ◽  
Stepped Chute ◽  
Uniform Equilibrium

Stepped spillways have been used for about 3500 years. The last few decades have seen the development of new construction materials, design techniques, and applications, for example, embankment overtopping protection systems. Although it is commonly acknowledged that free-surface aeration is significant in stepped chutes, experimental data are scarce, often limited to very steep slopes (α ~ 50°). This paper presents an experimental study conducted in a large-size stepped chute (α = 22°, h = 0.1 m, W = 1 m). Observations demonstrate the existence of a transition flow pattern for intermediate flow rates between nappe and skimming flows. Detailed air–water flow measurements were conducted in both transition and skimming flows, immediately downstream of the inception point of free-surface aeration where uniform equilibrium flow conditions were not achieved. In skimming flows, a complete characterization is developed for the distributions of void fraction, bubble count rate, and velocity, and flow resistance data are compared with other studies. Transition flows exhibit significantly different air–water flow properties. They are highly aerated, requiring the design of comparatively high chute sidewalls.Key words: stepped spillway, air entrainment, two-phase flow properties, skimming flow, transition flow.

scholarly journals Influence of aeration induced by piers on the starting position of the flow aeration and extreme pressures in stepped spillways

RBRH ◽  
2021 ◽  
Vol 26 ◽  
Author(s):  
Priscila dos Santos Priebe ◽  
Rute Ferla ◽  
Carolina Kuhn Novakoski ◽  
Aline Saupe Abreu ◽  
Eder Daniel Teixeira ◽  
...  
Keyword(s):  
Physical Model ◽  
Experimental Analysis ◽  
Flow Behavior ◽  
Flow Characteristics ◽  
Exceedance Probability ◽  
Stepped Spillway ◽  
Air Concentration ◽  
Stepped Spillways ◽  
Starting Position ◽  
Cavitation Phenomenon

ABSTRACT The operation of stepped spillways is limited by a range of discharges due to the risk of occurrence of the cavitation phenomenon and erosion on its steps. Since there is a demand for spillways with the possibility of overflow of greater discharges, the designs seek to increase the air concentration of the flow, which can occur through the installation of piers in the spillway in order to protect the structure from the above mentioned damage. The aim of this work is to analyze flow characteristics and extreme minimum and maximum pressures with non-exceedance probability of 0.1% and 99.9% acting next to the step edges of the spillway with aeration induced by piers through an experimental analysis in a physical model. Based on the results obtained, flow behavior was defined and equations for predicting the extreme pressures that occur along the stepped spillway with aeration induced by piers were proposed.

scholarly journals Stepped Spillways and Energy Dissipation: A Non-Uniform Step Length Approach

2019 ◽  
Vol 9 (23) ◽  
pp. 5071
Author(s):  
Abdelwanees Ashoor ◽  
Amin Riazi
Keyword(s):  
Energy Dissipation ◽  
Step Length ◽  
Maximum Energy ◽  
Stepped Spillway ◽  
Constant Number ◽  
Stepped Spillways ◽  
Interference Region ◽  
Different Types ◽  
Stepped Chute

A stepped spillway, which is defined as a spillway with steps on the chute, can be used to improve the energy dissipation of descending water. Although uniform stepped spillways have been studied comprehensively, non-uniform stepped spillways need more attention. In the interest of maximum energy dissipation, in this study, non-uniform stepped spillways were investigated numerically. To this end, within the range of skimming flow, four different types of non-uniform step lengths, including convex, concave, random, and semi-uniform configurations, were tested in InterFOAM. To evaluate the influence of non-uniform step lengths on energy dissipation, the height and number of steps in all models were fixed and equal to a constant number. The results indicated that in semi-uniform stepped spillways, when the ratio between the lengths of the successive steps is 1:3, a vortex interference region occurs within the two adjacent cavities of the entire stepped chute, and as a result, the energy dissipation increases by up to 20%.

Comparative analysis for estimation of the height of training wall of convergent stepped spillway

2015 ◽  
Vol 4 (2) ◽  
pp. 294
Author(s):  
Prafull Wadhai ◽  
Aniruddha Ghare ◽  
Narendra Deshpande ◽  
Avinash Vasudeo
Keyword(s):  
Comparative Analysis ◽  
Maximum Depth ◽  
Step Height ◽  
Stepped Spillway ◽  
Maximum Height ◽  
Stepped Spillways ◽  
Roller Compacted Concrete ◽  
Design Engineers ◽  
Experimental Findings ◽  
Stepped Chute

For a dam system with inadequate capacity of spillway, provision of (RCC) roller compacted concrete stepped spillways with converging training walls prove to be an appropriate alternative. Sufficient number of guidelines and literature references are available on the design of straight side walled stepped spillways. The need was felt to conduct the experiments on stepped spillways with convergent training walls, as limited literature is available. This paper presents the comparative analysis of an experimentation conducted on flow over convergent stepped spillways having 1:1 chute slope with 45o convergence angle for different step height ratios leading to different step height variations. The findings are presented in the form of expressions for the maximum depth of flow through the training walls required to accommodate the flow rate. The observed maximum depth of flow along the training walls also compared with estimated maximum height of the training wall as per the criteria available within literature and percentage variation is worked out taking into account the step height variation. Outcomes of the experimental findings are expected to be useful for assessment of height of training walls by the hydraulic design engineers involved in rehabilitation of existing dam system and also in design of the modified spillway system that is necessarily associated with convergent training walls and stepped chute.

scholarly journals Aeration and deaeration at bottom aeration devices on spillways

1994 ◽  
Vol 21 (3) ◽  
pp. 404-409 ◽  
Author(s):  
Hubert Chanson
Keyword(s):  
High Velocity ◽  
Flow Characteristics ◽  
Air Entrainment ◽  
Air Concentration ◽  
Concentration Data ◽  
Cavitation Damage ◽  
Downstream Flow ◽  
Bottom Outlets ◽  
The Impact ◽  
Impact Region

Aeration devices are introduced along chute spillways and at bottom outlets to prevent cavitation damage in high velocity flows. Bottom aerators are characterized by large quantities of air entrained along the jet interfaces and also by a strong deaeration process near the impact of the water jet with the spillway bottom. In this paper, the aeration and deaeration occurring respectively in the aeration region and in the impact region are reviewed. A reanalysis of air concentration data obtained on models provides information on the flow characteristics at the end of the impact region. These results enable an accurate initialization of the downstream flow calculations using the method developed by Chanson. Key words: bottom aeration devices, aerators, spillways, air entrainment, detrainment.

scholarly journals Experimental Investigation of Artificial Aeration on a Smooth Spillway with a Crest Pier

Water ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 1383 ◽  
Author(s):  
Juan Luna-Bahena ◽  
Oscar Pozos-Estrada ◽  
Víctor Ortiz-Martínez ◽  
Jesús Gracia-Sánchez
Keyword(s):  
Shock Waves ◽  
Hydraulic Structure ◽  
Standing Waves ◽  
Experimental Tests ◽  
Air Entrainment ◽  
Air Concentration ◽  
Cavitation Damage ◽  
Stepped Spillways ◽  
Artificial Aeration ◽  
And Shock Waves

Crest piers placed on overflow spillways induce standing waves at the downstream end of them and the supercritical flow expands after flowing past the rear of the pier. The expanding flow from each side of a pier will intersect and form disturbances or shock waves that travel laterally as they move downstream and eventually reach the chute sidewalls. Recently, investigations regarding crest piers are related with artificial aeration on stepped spillways to eliminate the risk of cavitation damage. However, there is a lack of studies on standing and shock waves in smooth spillways concerning the air entrainment into the flow in presence of crest piers. This paper presents the study of the combined effect on air entrainment of a crest pier and an aerator on the bottom of a smooth spillway (configuration 1). For comparison, experimental tests were developed in the spillway without pier, that is in presence of aerator only (configuration 2). The configuration 1 results show that the air concentration distribution on the spillway bottom across the width and length of the chute increases in comparison with configuration 2, reducing even more the risk of cavitation damage and enhancing the safety of the hydraulic structure.

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