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 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 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 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 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 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.

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 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.

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 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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