scholarly journals Air entrainment and energy dissipation on Gabion stepped weirs

2014 ◽  
Author(s):  
Davide Wuthrich ◽  
Hubert Chanson
Keyword(s):  
Energy Dissipation ◽  
Air Entrainment

scholarly journals Energy dissipation efficiency as a new variable in the empirical correlation of total dissolved gas

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jingying Lu ◽  
Xiaolong Cheng ◽  
Zhenhua Wang ◽  
Ran Li ◽  
Jingjie Feng ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Standard Error ◽  
Air Entrainment ◽  
Empirical Equations ◽  
Generation Process ◽  
Field Observations ◽  
Dissolved Gas ◽  
Total Dissolved Gas ◽  
Future Work ◽  
Hydropower Stations

AbstractTotal dissolved gas (TDG) supersaturation, which occurs during dam spilling, may result in fish bubble disease and mortality. Many studies have been conducted to identify the factors pertaining to TDG generation, such as the spilling discharge and tailwater depth. Additionally, the energy dissipation efficiency should be considered due to its effect on the air entrainment, which influences the TDG generation process. According to the TDG field observations of 49 cases at Dagangshan and Xiluodu hydropower stations, the TDG was positively related to the energy dissipation efficiency, tailwater depth and discharge per unit width. A correlation between the generated TDG level and these factors was established. The empirical equations proposed by the USACE were calibrated, and the TDG level estimation performance was compared with the established correlation for 25 spillage cases at seven other dams. Among the considered cases, the standard error of the TDG estimation considering the energy dissipation efficiency was 5.7%, and those for the correlations obtained using the USACE equations were 13.0% and 10.0%. The findings indicated that the energy dissipation efficiency considerably influenced the TDG level, and its consideration helped enhance the precision of the TDG estimation. Finally, the generality of this approach and future work were discussed.

scholarly journals Experimental Characterization of the Hydraulic Jump Profile and Velocity Distribution in a Stilling Basin Physical Model

Water ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 1758
Author(s):  
Juan Macián-Pérez ◽  
Francisco Vallés-Morán ◽  
Santiago Sánchez-Gómez ◽  
Marco De-Rossi-Estrada ◽  
Rafael García-Bartual
Keyword(s):  
Free Surface ◽  
Energy Dissipation ◽  
Velocity Distribution ◽  
Physical Model ◽  
Hydraulic Jump ◽  
Surface Profile ◽  
Air Entrainment ◽  
Stilling Basin ◽  
Free Surface Profile ◽  
Stilling Basins

The study of the hydraulic jump developed in stilling basins is complex to a high degree due to the intense velocity and pressure fluctuations and the significant air entrainment. It is this complexity, bound to the practical interest in stilling basins for energy dissipation purposes, which brings the importance of physical modeling into the spotlight. However, despite the importance of stilling basins in engineering, bibliographic studies have traditionally focused on the classical hydraulic jump. Therefore, the objective of this research was to study the characteristics of the hydraulic jump in a typified USBR II stilling basin, through a physical model. The free surface profile and the velocity distribution of the hydraulic jump developed within this structure were analyzed in the model. To this end, an experimental campaign was carried out, assessing the performance of both, innovative techniques such as the time-of-flight camera and traditional instrumentation like the Pitot tube. The results showed a satisfactory representation of the free surface profile and the velocity distribution, despite some discussed limitations. Furthermore, the instrumentation employed revealed the important influence of the energy dissipation devices on the flow properties. In particular, relevant differences were found for the hydraulic jump shape and the maximum velocity positions within the measured vertical profiles, when compared to classical hydraulic jumps.

scholarly journals Energy Dissipation Structures: Influence of Aeration in Supercritical Flows

Proceedings ◽  
2018 ◽  
Vol 7 (1) ◽  
pp. 5
Author(s):  
Juan José Rebollo ◽  
David López ◽  
Tamara Ramos ◽  
Luis Garrote
Keyword(s):  
Energy Dissipation ◽  
Turbulent Flows ◽  
Flood Control ◽  
Air Entrainment ◽  
Air Concentration ◽  
Basin Water ◽  
Manning Roughness ◽  
Intake Flow ◽  
Supercritical Flows ◽  
Adequate Design

Adequate design of energy dissipation structures is essential for effective flood control. The effect of aeration on water flow has been one of most analyzed phenomena during the last decades due to its influence on hydraulic structures. The purpose of this study is to characterize the influence of aeration on the boundary friction in supercritical and fully turbulent flows. Our analysis is based on a physical model to reproduce these phenomena and consists of a spillway chute 6.5 m high, followed by a 10 m length and 2 m high still basin. Water and air are supplied by a pump and compressors, and is controlled at the entrance by several valves and flowmeters, while the channel is monitored to measure the velocity profile and air concentration in the intake flow to the still basin. Velocity results included in this paper show the relation between air concentration and energy dissipation by friction. To determine this relation, Manning roughness numbers have been obtained for all scenarios. It has been found that greater air entrainment implies acceleration of the flow, since friction is the main energy dissipation mechanism in open channels flow.

scholarly journals Hydraulics, Air Entrainment, and Energy Dissipation on a Gabion Stepped Weir

2014 ◽  
Vol 140 (9) ◽  
pp. 04014046 ◽  
Author(s):  
Davide Wüthrich ◽  
Hubert Chanson
Keyword(s):  
Energy Dissipation ◽  
Air Entrainment

scholarly journals Hydraulic performance of helical-step dropshaft

2021 ◽  
Author(s):  
Weichen Ren ◽  
Jianhua Wu ◽  
Fei Ma ◽  
Shangtuo Qian
Keyword(s):  
Energy Dissipation ◽  
Pressure Distribution ◽  
Cavitation Erosion ◽  
Air Entrainment ◽  
Flow Regimes ◽  
High Energy ◽  
Energy Dissipation Rate ◽  
Attractive Alternative ◽  
Air Concentration ◽  
Flow Energy

Abstract Aiming to achieve energy dissipation and prevention of cavitation erosion, a kind of dropshaft in urban drainage systems, called helical-step dropshaft, is introduced in this paper. It dissipates flow energy by means of step geometry and prevent cavitation erosion through air entrainment. To verify its availability, the hydraulic characteristics of the helical-step dropshaft were experimentally investigated, including the flow regimes, the efficiency of energy dissipation, characteristics of air entrainment and pressure distribution. The results demonstrate that, even for a large discharge, flow can be discharged smoothly and steadily, and a high energy-dissipation rate of over 87% is achieved. There are three distinct flow regimes observed in the dropshaft, namely nappe flow, mixed flow and skimming flow. Moreover, there is no less than 1.6% air concentration and a reasonable pressure distribution on the step surface. This study provides an attractive alternative for the design of drop structures.

Energy dissipation in a deep tailwater stilling basin with partial flaring gate piers

2020 ◽  
Vol 47 (5) ◽  
pp. 523-533
Author(s):  
Zhao Zhou ◽  
Junxing Wang ◽  
David Z. Zhu
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Hydraulic Jump ◽  
High Speed ◽  
Air Entrainment ◽  
Water Jet ◽  
Upstream Region ◽  
Level Energy ◽  
Stilling Basin

Flaring gate piers (FGPs) have been used to increase energy dissipation in stilling basins downstream of spillways. For projects with a low water head and large unit discharge together with a deep tailwater level, energy dissipation inside a conventional stilling basin is usually insufficient. This paper proposes a new partial flaring gate pier (partial FGP) scheme to intensify the energy dissipation inside the stilling basin. The results for the no FGP scheme, the conventional FGP scheme, and the partial FGP scheme were compared using a physical model study and numerical simulations. It was found that the partial FGP scheme (the alternation of flaring and no flaring gate piers in chambers) can contain the submerged hydraulic jump and high-speed water jet in the upstream region of the stilling basin. Thus, the water jet from the FGP chamber was forced to laterally diffuse, thereby intensifying the shear friction and turbulent kinetic energy and forming a vertical vortex from the bottom to the surface. Compared with the other two schemes, the flow pattern in the partial FGP scheme was improved significantly with much deeper air entrainment depth inside the stilling basin and much lower turbulent kinetic energy in the outgoing flow. The mean velocity of the outgoing flow also decreased by more than 20%. The common problems of secondary hydraulic jump outside the stilling basin were eliminated.

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 Experimental and Numerical Study of the Effects of Geometric Appendance Elements on Energy Dissipation over Stepped Spillway

Water ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 957
Author(s):  
Amir Ghaderi ◽  
Saeed Abbasi
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Numerical Study ◽  
Air Entrainment ◽  
Computational Procedure ◽  
Stepped Spillway ◽  
Construction Costs ◽  
Geometric Configurations ◽  
Inception Point

In the stepped spillway, the steps, by providing an artificial roughening bed, dissipate the flow of energy more than other types of spillways, so the construction costs for stilling basin are reduced. However, what is important in this type of spillway is increasing the effectiveness of steps in the rate of energy dissipation. The present study deals with experimental and numerical simulations regarding the influence of geometric appendance elements on the steps and its impact on the energy dissipation performances, flow patterns properties, turbulent kinetic energy, flow resistance and the Darcy roughness. The localization of inception point of air entrainment is also assessed. To this aim, different configurations are taken into account. The computational procedure is validated with experimental results and then used to test the hydraulic behavior of different geometric configurations. The results showed that the appendance elements on the steps increased the turbulent kinetic energy (TKE) values and Darcy–Weisbach friction and the energy dissipation increased significantly. By reducing the height of the elements, energy dissipation and the TKE value increase more significantly. With the appendance elements on step, the air entrainment inception locations a positioning further upstream than the flat step stepped spillway.

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