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.

Air-water flow in bottom outlets

2000 ◽  
Vol 27 (3) ◽  
pp. 454-462 ◽  
Author(s):  
Jürg Speerli ◽  
Willi H Hager
Keyword(s):  
Water Flow ◽  
High Velocity ◽  
Flow Characteristics ◽  
Design Procedure ◽  
Air Entrainment ◽  
Design Guidelines ◽  
Air Concentration ◽  
Tunnel Length ◽  
Mixture Flow ◽  
Bottom Outlets

Bottom outlets involve high-velocity air-water flow. Depending on the tunnel length, both air entrainment and air detrainment processes are significant. These processes are evaluated using a hydraulic model consisting of a long rectangular tunnel with a bottom slope larger than the critical slope. Expressions are presented for the maximum air concentration and its streamwise development along the tunnel. A prediction of mixture flow depth along the tunnel is developed. Design guidelines are presented relating to the flow pattern required, the air supply system, and the downstream submergence. The effect of tunnel length on the development of mixture flow characteristics is also outlined. A typical example shows the design procedure for bottom outlets.Key words: air entrainment, air-water flow, high-velocity flow, tunnel flow.

Effect of Entrained Air on Cavitation Damage

1974 ◽  
Vol 1 (1) ◽  
pp. 97-107 ◽  
Author(s):  
S. O. Russell ◽  
G. J. Sheehan
Keyword(s):  
High Velocity ◽  
Additional Data ◽  
Air Entrainment ◽  
Test Facility ◽  
Hydraulic Structures ◽  
Cavitation Damage ◽  
Water Flows ◽  
Velocity Flow ◽  
High Head ◽  
Entrained Air

When water flows at high velocity over a surface, quite small boundary irregularities may trigger cavitation which can, in turn, cause extensive damage. Concrete surfaces downstream from high head outlet gates are particularly vulnerable to cavitation damage.Operating experience and previous experimental work suggest that cavitation damage can be greatly reduced and, in some cases, eliminated by entrained air in the water.Experiments were carried out with a special high head test facility in Vancouver to obtain additional data on the effect of air entrainment. These tests confirmed its effectiveness. In this paper, previous evidence is reviewed, the experiments are described, and the results presented. Finally suggestions are made about the design of hydraulic structures which involve high velocity flow.

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.

Reduction of cavitation on spillways by induced air entrainment

1991 ◽  
Vol 18 (3) ◽  
pp. 358-377 ◽  
Author(s):  
James A. Kells ◽  
C. D. Smith
Keyword(s):  
High Velocity ◽  
Air Entrainment ◽  
Unit Discharge ◽  
Cavitation Damage ◽  
Discharge Rates ◽  
Sufficient Detail ◽  
Velocity Flow ◽  
Finished Surface ◽  
High Head ◽  
Forced Aeration

Spillways for medium and high head dams may be exposed to high velocity flows and the associated destructive phenomenon of cavitation. Cavitation may occur at rough spots in the surface of the chute or tunnel, at local discontinuities in the finished surface such as construction joints, and at locations along critical flow profiles having significant deviations from design specifications. This paper addresses, on the basis of a review of the literature, a method for preventing or reducing cavitation damage on spillways through the use of spillway aerators. While the ability of induced or forced aeration to reduce or eliminate cavitation has been known for many years, it is only in relatively recent times that the aeration mechanism has been used to this advantage on spillways subject to high velocity flow. The recent application of aerators to spillway design is related, in part, to the trend toward higher head dams and larger design unit discharge rates. Design considerations and criteria for spillway aerators are presented in the paper, and the use of physical hydraulic models to make determinations of aerator performance is discussed. The intent of the paper is to provide a document with sufficient detail and scope to be useful as a first resource for spillway design practitioners. Key words: aerator design, air entrainment, cavitation, design criteria, high dam, model – prototype comparison, physical hydraulic model, spillway, spillway aeration.

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.

High-speed jet flows over spillway aerators

2002 ◽  
Vol 29 (6) ◽  
pp. 885-898 ◽  
Author(s):  
Mehmet Ali Kökpınar ◽  
Mustafa Göğüş
Keyword(s):  
High Speed ◽  
Scale Effects ◽  
Pressure Fluctuations ◽  
Air Entrainment ◽  
Water Jet ◽  
Jet Flows ◽  
Excessive Pressure ◽  
Jet Length ◽  
The Impact ◽  
Impact Region

The characteristics of high-speed air-entrained jet flow over a spillway aerator were investigated using experimental data. Three different ramp designs (as well as the case of no ramp) were tested in a channel where the bed slope was adjusted to 0, 0.17, and 0.57, respectively. The effects of aerator geometry and flow condition on the air-entrainment process within the water jet and on the pressure fluctuations in the impact region are the main focus of the investigation. An extensive data analysis was performed for data obtained from this study and from a similar laboratory study conducted by another investigator. Experimental relations were derived for nondimensional parameters of jet length, aerator cavity subpressure number, and aeration rates through the lower and upper nappes of the water jet. Scale effects for lower nappe aeration and aerator cavity subpressure number were considered and a good correlation was determined with prototype aerator measurements of Emborcaçao, Foz do Areia, and Keban dams for lower nappe aeration and Guri Dam for aerator cavity subpressure numbers. An aerator without a ramp may be subjected to excessive pressure fluctuations at the impact region due to insufficient air entrainment. Key words: air entrainment, aerator, scale effect, jet length, cavity subpressure.

An improved de Laval nozzle experiment

2021 ◽  
pp. 030641902110341
Author(s):  
Nicholas Goodman ◽  
Brian J Leege ◽  
Peter E Johnson
Keyword(s):  
Data Acquisition ◽  
Laval Nozzle ◽  
Flow Characteristics ◽  
Data Acquisition System ◽  
Isentropic Flow ◽  
Hands On ◽  
De Laval Nozzle ◽  
Physical Phenomena ◽  
The Impact ◽  
The Relationship

Exposing students to hands-on experiments has been a common approach to illustrating complex physical phenomena that have been otherwise modelled solely mathematically. Compressible, isentropic flow in a duct is an example of such a phenomenon, and it is often demonstrated via a de Laval nozzle experiment. We have improved an existing converging/diverging nozzle experiment so that students can modify the location of the normal shock that develops in the diverging portion to better understand the relationship between the shock and the pressure. We have also improved the data acquisition system for this experiment and explained how visualisation of the standing shock is now possible. The results of the updated system demonstrate that the accuracy of the isentropic flow characteristics has not been lost. Through pre- and post-laboratory quizzes, we show the impact on student learning as well.

The flow characteristics around bridge piers under the impact of a ship

2020 ◽  
Vol 32 (6) ◽  
pp. 1165-1177
Author(s):  
Yan-fen Geng ◽  
Hua-qiang Guo ◽  
Xing Ke
Keyword(s):  
Flow Characteristics ◽  
Bridge Piers ◽  
The Impact

scholarly journals Virus Transmission Risk in Urban Rail Systems: Microscopic Simulation-Based Analysis of Spatio-Temporal Characteristics

2021 ◽  
pp. 036119812110101
Author(s):  
Jiali Zhou ◽  
Haris N. Koutsopoulos
Keyword(s):  
Public Transportation ◽  
Virus Transmission ◽  
Flow Characteristics ◽  
Transportation Systems ◽  
Transmission Risk ◽  
Microscopic Simulation ◽  
Spatial And Temporal Patterns ◽  
Subway System ◽  
Public Transportation Systems ◽  
The Impact

The transmission risk of airborne diseases in public transportation systems is a concern. This paper proposes a modified Wells-Riley model for risk analysis in public transportation systems to capture the passenger flow characteristics, including spatial and temporal patterns, in the number of boarding and alighting passengers, and in number of infectors. The model is used to assess overall risk as a function of origin–destination flows, actual operations, and factors such as mask-wearing and ventilation. The model is integrated with a microscopic simulation model of subway operations (SimMETRO). Using actual data from a subway system, a case study explores the impact of different factors on transmission risk, including mask-wearing, ventilation rates, infectiousness levels of disease, and carrier rates. In general, mask-wearing and ventilation are effective under various demand levels, infectiousness levels, and carrier rates. Mask-wearing is more effective in mitigating risks. Impacts from operations and service frequency are also evaluated, emphasizing the importance of maintaining reliable, frequent operations in lowering transmission risks. Risk spatial patterns are also explored, highlighting locations of higher risk.

scholarly journals Airflow Characteristics According to the Change in the Height and Porous Rate of Building Roofs for Efficient Installation of Small Wind Power Generators

2021 ◽  
Vol 13 (10) ◽  
pp. 5688
Author(s):  
Jangyoul You ◽  
Kipyo You ◽  
Minwoo Park ◽  
Changhee Lee
Keyword(s):  
Wind Speed ◽  
Wind Power ◽  
Turbulence Intensity ◽  
Flow Characteristics ◽  
High Porosity ◽  
Power Generators ◽  
Speed Reduction ◽  
Reduction Effect ◽  
Wind Power Generators ◽  
The Impact

In this paper, the air flow characteristics and the impact of wind power generators were analyzed according to the porosity and height of the parapet installed in the rooftop layer. The wind speed at the top was decreasing as the parapet was installed. However, the wind speed reduction effect was decreasing as the porosity rate increased. In addition, the increase in porosity significantly reduced turbulence intensity and reduced it by up to 40% compared to no railing. In the case of parapets with sufficient porosity, the effect of reducing turbulence intensity was also increased as the height increased. Therefore, it was confirmed that sufficient parapet height and high porosity reduce the effect of reducing wind speed by parapets and significantly reducing the turbulence intensity, which can provide homogeneous wind speed during installation of wind power generators.

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