scholarly journals Stepped spillways with aerators: hydrodynamic pressures and air entrainment

RBRH ◽  
2021 ◽  
Vol 26 ◽  
Author(s):  
Rute Ferla ◽  
Carolina Kuhn Novakoski ◽  
Priscila dos Santos Priebe ◽  
Mauricio Dai Prá ◽  
Marcelo Giulian Marques ◽  
...  
Keyword(s):  
Experimental Study ◽  
Physical Model ◽  
Air Entrainment ◽  
Specific Flow ◽  
Flow Rates ◽  
Stepped Spillways ◽  
Entrainment Coefficient ◽  
Flow Through ◽  
New Equation ◽  
Stepped Chute

ABSTRACT The possibility of damage due to the phenomenon of cavitation leads the design of stepped spillways considering maximum specific discharges of 15 to 30 m2/s, a limit considerably lower than that practiced on smooth chutes. Aerators promote the insertion of air in the flow, allowing for the increase of specific flow rates. This work analyzes the pressures on the vertical faces of the steps and the air entrainment coefficient in the flow, through an experimental study in a physical model with a stepped chute angle of 53.13o, considering the installation of aerators in different places of the channel. Comparing the tested conditions with the natural aeration, it is concluded that the installation of the aerator does not change the magnitude of the minimum extreme hydrodynamic pressures, but anticipates the beginning of the flow aeration. A new equation is proposed to estimate the air entrainment coefficient, as well as a methodology for forecasting extreme pressures on the vertical faces of the steps, both valid in the range 3.0 ≤ Fr ≤ 6.0.

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 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 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 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 Performance and Design of a Stepped Spillway Aerator

Water ◽  
2022 ◽  
Vol 14 (2) ◽  
pp. 153
Author(s):  
Stéphane Terrier ◽  
Michael Pfister ◽  
Anton J. Schleiss
Keyword(s):  
Concentration Distribution ◽  
Water Discharge ◽  
Air Entrainment ◽  
Stepped Spillway ◽  
Flow Depth ◽  
Air Concentration ◽  
Stepped Spillways ◽  
Jet Impact ◽  
Entrainment Coefficient ◽  
Pressure Water

Stepped spillways are frequently limited to specific discharges under around 30 m2/s due to concerns about potential cavitation damages. A small air concentration can prevent such damages and the design of bottom aerators is well established for smooth chutes. The purpose of this study is to systematically investigate the performance of a deflector aerator at the beginning of stepped chutes. Six parameters (chute angle, step height, approach flow depth, approach flow Froude number, deflector angle and deflector height) are varied in a physical model. The spatial air concentration distribution downstream of the aerator, the cavity sub-pressure, water discharge and air discharges are measured. The results describe the commonly used air entrainment coefficient, the jet length, as well as the average and bottom air concentration development to design an aerator. The lowest bottom air concentration measured in all tests is higher than the air concentration recommended in literature to protect against cavitation damages. And, unlike smooth chutes, there appears to be no significant air detrainment downstream of the jet impact. One deflector aerator seems therefore sufficient to provide protection of a stepped spillway.

scholarly journals Analysis of Performance of the Wind-Driven Pulverizing Aerator Based on Average Wind Speeds in the Conditions of Góreckie Lake

Energies ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2796
Author(s):  
Andrzej Osuch ◽  
Ewa Osuch ◽  
Stanisław Podsiadłowski ◽  
Piotr Rybacki
Keyword(s):  
Mathematical Model ◽  
Wind Speed ◽  
Water Pump ◽  
Average Wind Speed ◽  
Flow Rates ◽  
Wind Speeds ◽  
Average Wind ◽  
Flow Through ◽  
Analysis Of Performance ◽  
Research Period

In the introduction to this paper, the characteristics of Góreckie lake and the construction and operation of the wind-driven pulverizing aerator are presented. The purpose of this manuscript is to determine the efficiency of the pulverizing aerator unit in the windy conditions of Góreckie Lake. The efficiency of the pulverization aerator depends on the wind conditions at the lake. It was necessary to conduct thorough research to determine the efficiency of water flow through the pulverization segment (water pump). It was necessary to determine the rotational speed of the paddle wheel, which depended on the average wind speed. Throughout the research period, measurements of hourly average wind speed were carried out. It was possible to determine the efficiency of the machine by developing a dedicated mathematical model. The latest method was used in the research, consisting of determining the theoretical volumetric flow rates of water in the pulverizing aerator unit, based on average hourly wind speeds. Pulverization efficiency under the conditions of Góreckie Lake was determined based on 6600 average wind speeds for spring, summer and autumn, 2018. Based on the model, the theoretical efficiency of the machine was calculated, which, under the conditions of Góreckie Lake, amounted to 75,000 m3 per year.

scholarly journals Transient Pressure-Driven Electroosmotic Flow through Elliptic Cross-Sectional Microchannels with Various Eccentricities

Computation ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 27
Author(s):  
Nattakarn Numpanviwat ◽  
Pearanat Chuchard
Keyword(s):  
Laplace Transform ◽  
Electroosmotic Flow ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Mathieu Functions ◽  
Navier Stokes Equations ◽  
Flow Rates ◽  
Elliptic Cross ◽  
Flow Through ◽  
Relative Errors

The semi-analytical solution for transient electroosmotic flow through elliptic cylindrical microchannels is derived from the Navier-Stokes equations using the Laplace transform. The electroosmotic force expressed by the linearized Poisson-Boltzmann equation is considered the external force in the Navier-Stokes equations. The velocity field solution is obtained in the form of the Mathieu and modified Mathieu functions and it is capable of describing the flow behavior in the system when the boundary condition is either constant or varied. The fluid velocity is calculated numerically using the inverse Laplace transform in order to describe the transient behavior. Moreover, the flow rates and the relative errors on the flow rates are presented to investigate the effect of eccentricity of the elliptic cross-section. The investigation shows that, when the area of the channel cross-sections is fixed, the relative errors are less than 1% if the eccentricity is not greater than 0.5. As a result, an elliptic channel with the eccentricity not greater than 0.5 can be assumed to be circular when the solution is written in the form of trigonometric functions in order to avoid the difficulty in computing the Mathieu and modified Mathieu functions.

scholarly journals Evaluation of a Humidified Nasal High-Flow Oxygen System, Using Oxygraphy, Capnography and Measurement of Upper Airway Pressures

2011 ◽  
Vol 39 (6) ◽  
pp. 1103-1110 ◽  
Author(s):  
J. E. Ritchie ◽  
A. B. Williams ◽  
C. Gerard ◽  
H. Hockey
Keyword(s):  
Healthy Volunteers ◽  
Airway Pressure ◽  
Gas Flow ◽  
Air Entrainment ◽  
High Flow ◽  
Positive Pressure ◽  
Mean Airway Pressure ◽  
Flow Rates ◽  
Oxygen Fraction ◽  
Airway Pressures

In this study, we evaluated the performance of a humidified nasal high-flow system (Optiflow™, Fisher and Paykel Healthcare) by measuring delivered FiO2 and airway pressures. Oxygraphy, capnography and measurement of airway pressures were performed through a hypopharyngeal catheter in healthy volunteers receiving Optiflow™ humidified nasal high flow therapy at rest and with exercise. The study was conducted in a non-clinical experimental setting. Ten healthy volunteers completed the study after giving informed written consent. Participants received a delivered oxygen fraction of 0.60 with gas flow rates of 10, 20, 30, 40 and 50 l/minute in random order. FiO2, FEO2, FECO2 and airway pressures were measured. Calculation of FiO2 from FEO2 and FECO2 was later performed. Calculated FiO2 approached 0.60 as gas flow rates increased above 30 l/minute during nose breathing at rest. High peak inspiratory flow rates with exercise were associated with increased air entrainment. Hypopharyngeal pressure increased with increasing delivered gas flow rate. At 50 l/minute the system delivered a mean airway pressure of up to 7.1 cmH2O. We believe that the high gas flow rates delivered by this system enable an accurate inspired oxygen fraction to be delivered. The positive mean airway pressure created by the high flow increases the efficacy of this system and may serve as a bridge to formal positive pressure systems.

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