Research on scale effects on flows over weirs has been conducted on a limited basis, primarily focusing on flows upstream of a single-type weir, such as ogee, broad-crested, and sharp-crested (linear and non-linear) w...Research on scale effects on flows over weirs has been conducted on a limited basis, primarily focusing on flows upstream of a single-type weir, such as ogee, broad-crested, and sharp-crested (linear and non-linear) weirs. However, the scale effects downstream of these single-type weirs have not been thoroughly investigated. This study examined the scale effects on flows over a combined weir system consisting of an ogee weir and a sharp-crested weir, both upstream and downstream, utilizing physical modeling at a 1:33.33 scale based on Froude similarity and three-dimensional (3D) computational fluid dynamics (CFD) modeling. The sharp-crested weir in this study was represented by two sluice gates that remain closed and submerged during flood events. The experimental data confirmed that the equivalent discharge coefficients of the combined weir system behaved similarly to those of a sharp-crested weir across various H/P (where H is the total head, and P is the weir height) values. However, scale effects on the discharge rating curve due to surface tension and viscosity could only be minimized when H/P > 0.4, Re > 26 959, and We > 240 (where Re and We are the Reynolds and Weber numbers, respectively), provided that the water depth exceeded 0.042 m above the crest. Additionally, Re greater than 4 × 104 was necessary to minimize scale effects caused by viscosity in flows in the spillway channel and stilling basin (with baffle blocks). The limiting criteria aligned closely with existing literature. This study offers valuable insights for practical applications in hydraulic engineering in the future.展开更多
In order to explore the advantages of the triangular weir fishway and the influence of the angle of the triangular weir fishway on fish migration,this paper simulates the internal flow field and free surface of the fi...In order to explore the advantages of the triangular weir fishway and the influence of the angle of the triangular weir fishway on fish migration,this paper simulates the internal flow field and free surface of the fishway by using large eddy simulation(LES)and volume of fluid(VOF)method,respectively,and analyzes the hydraulic characteristics of the triangular weir at the three angles,where for the analysis of turbulent structure,omega(Ω)eddy identification is also used.And based on the analysis results,the length of the pool chamber and the height of obstacles were changed to obtain a more stable flow regime.The results show that the main flow is obvious,the turbulent kinetic energy distribution is regular and small in value,and the angle has an effect on the return flow.The vortex structure mainly existed in the mainstream area with high flow velocity,the air-liquid interface and the porosity,and was distributed transversely.90°triangular weir had the largest vortex structure,and 105°triangular weir had the smallest.75°triangular weir fishway could effectively attenuate the energy of the main stream,and the area of high velocity flow was small,which made the migratory conditions more favorable.Adding obstructions to the mainstem area can reduce flow velocity and turbulent kinetic energy.The triangular weir structure can improve the flow structure of the fishway,and the different angles and water depths provide a variety of flow conditions for a variety of fish migrations,providing new ideas for the fishway.展开更多
Weirs are a type of hydraulic structure, used for water level adjustment, flow measurement, and diversion of water in irrigation systems. In this study, experiments were conducted on sharp-crested weirs under free-flo...Weirs are a type of hydraulic structure, used for water level adjustment, flow measurement, and diversion of water in irrigation systems. In this study, experiments were conducted on sharp-crested weirs under free-flow conditions and an optimization method was used to determine the best form of the discharge coefficient equation based on the coefficient of determination （R2） and root mean square error （RMSE）. The ability of the numerical method to simulate the flow over the weir was also investigated using Fluent software. Results showed that, with an increase of the ratio of the head over the weir crest to the weir height （h/P）, the discharge coefficient decreased nonlinearly and reached a constant value of 0.7 for hiP 〉 0.6. The best form of the discharge coefficient equation predicted the discharge coefficient well and percent errors were within a ±5% error limit. Numerical results of the discharge coefficient showed strong agreement with the experimental data. Variation of the discharge coefficient with Reynolds numbers showed that the discharge coefficient reached a constant value of 0.7 when hiP 〉 0.6 and Re 〉 20000.展开更多
基金supported by the Ministry of Public Works and Housing of Indonesia and Parahyangan Catholic University(Grant No.II/PD/2023-07/02-SJ).
文摘Research on scale effects on flows over weirs has been conducted on a limited basis, primarily focusing on flows upstream of a single-type weir, such as ogee, broad-crested, and sharp-crested (linear and non-linear) weirs. However, the scale effects downstream of these single-type weirs have not been thoroughly investigated. This study examined the scale effects on flows over a combined weir system consisting of an ogee weir and a sharp-crested weir, both upstream and downstream, utilizing physical modeling at a 1:33.33 scale based on Froude similarity and three-dimensional (3D) computational fluid dynamics (CFD) modeling. The sharp-crested weir in this study was represented by two sluice gates that remain closed and submerged during flood events. The experimental data confirmed that the equivalent discharge coefficients of the combined weir system behaved similarly to those of a sharp-crested weir across various H/P (where H is the total head, and P is the weir height) values. However, scale effects on the discharge rating curve due to surface tension and viscosity could only be minimized when H/P > 0.4, Re > 26 959, and We > 240 (where Re and We are the Reynolds and Weber numbers, respectively), provided that the water depth exceeded 0.042 m above the crest. Additionally, Re greater than 4 × 104 was necessary to minimize scale effects caused by viscosity in flows in the spillway channel and stilling basin (with baffle blocks). The limiting criteria aligned closely with existing literature. This study offers valuable insights for practical applications in hydraulic engineering in the future.
基金supported by the National Natural Science Foundation of China(Grant No.52069009).
文摘In order to explore the advantages of the triangular weir fishway and the influence of the angle of the triangular weir fishway on fish migration,this paper simulates the internal flow field and free surface of the fishway by using large eddy simulation(LES)and volume of fluid(VOF)method,respectively,and analyzes the hydraulic characteristics of the triangular weir at the three angles,where for the analysis of turbulent structure,omega(Ω)eddy identification is also used.And based on the analysis results,the length of the pool chamber and the height of obstacles were changed to obtain a more stable flow regime.The results show that the main flow is obvious,the turbulent kinetic energy distribution is regular and small in value,and the angle has an effect on the return flow.The vortex structure mainly existed in the mainstream area with high flow velocity,the air-liquid interface and the porosity,and was distributed transversely.90°triangular weir had the largest vortex structure,and 105°triangular weir had the smallest.75°triangular weir fishway could effectively attenuate the energy of the main stream,and the area of high velocity flow was small,which made the migratory conditions more favorable.Adding obstructions to the mainstem area can reduce flow velocity and turbulent kinetic energy.The triangular weir structure can improve the flow structure of the fishway,and the different angles and water depths provide a variety of flow conditions for a variety of fish migrations,providing new ideas for the fishway.
文摘Weirs are a type of hydraulic structure, used for water level adjustment, flow measurement, and diversion of water in irrigation systems. In this study, experiments were conducted on sharp-crested weirs under free-flow conditions and an optimization method was used to determine the best form of the discharge coefficient equation based on the coefficient of determination （R2） and root mean square error （RMSE）. The ability of the numerical method to simulate the flow over the weir was also investigated using Fluent software. Results showed that, with an increase of the ratio of the head over the weir crest to the weir height （h/P）, the discharge coefficient decreased nonlinearly and reached a constant value of 0.7 for hiP 〉 0.6. The best form of the discharge coefficient equation predicted the discharge coefficient well and percent errors were within a ±5% error limit. Numerical results of the discharge coefficient showed strong agreement with the experimental data. Variation of the discharge coefficient with Reynolds numbers showed that the discharge coefficient reached a constant value of 0.7 when hiP 〉 0.6 and Re 〉 20000.
