Geometry of the chute blocks in stilling basins plays a significant role in size and type of these structures. One of the most influencing factors in the design of the blocks is the fluctuating pressure which may cause fatigue on the blocks. Despite investigations conducted by many researchers, there is not enough information about the pressure fluctuation around chute blocks in compacted stilling basins such as Saint Anthony Falls (SAF) basins. In this paper, the results of a naval experimental work and measurement of pressure fluctuations around chute blocks of SAF stilling basins are reported. The results show that the pressure fluctuations around the chute blocks cannot be overlooked in designing such structures. The variation of pressure fluctuation with Froude number of incoming supercritical flow at various faces of the chute block is reported, which shows an increasing trend of pressure fluctuation. It is also observed that the submergence of hydraulic jump will decreasingly affect the pressure fluctuations. The trend of variations will follow different patterns at the different faces of the block.

Induced total pressure by flow, including mean and fluctuating components, around a selected chute block in SAF stilling basins downstream of an ogee spillway was studied. Several pressure holes were selected on various faces of a selected chute block to get enough information regarding the total pressure field. This paper reports the results of an experimental work and measurement of mean and fluctuation pressures around chute blocks of SAF stilling basins. The observations showed that the maximum total pressure varies inversely with Froude number of incoming flow while its position of occurrence follows a quadratic polynomial relationship. Statistical analysis also showed that the peak instantaneous pressure fluctuations could be as large as ±4.5 times the RMS value.It is concluded that pressure fluctuation around the chute blocks may double the magnitude of pressure field around the chute blocks and can not be overlooked in designing such appurtenances.

One of the ways to prevent creating negative pressure and cavitation in spillways is to introduce air into the flow over the spillways. Understanding the distribution of air concentration variations along the spillway is of significant importance for estimating the aeration level. This study explores the application of GPR and SVM molels in predicting air concentration. To achieve this, a dataset of 2268 laboratory experiments obtained from hydraulic models of chute spillways was utilized in the modeling process. Various input models were defined based on different combinations of measured parameters. The results demonstrate the high capability of both methods in estimating the required air concentration over the spillway. In predicting air concentration in the chute spillway under artificial aeration conditions, flow discharge (QW), longitudinal distance ratio from the end of the deflector to the channel width (L/W), and depth ratio (perpendicular to the spillway) to channel width (Y/W) significantly influenced the outcomes. Statistical indices, including R, DC, and RMSE for this case were 0.9214, 0.8451, and 1.008, respectively, in the GPR, and 0.9333, 0.8662, and 0.937 in the SVM. For scenarios without artificial aeration, the model with input parameters QW, L/W, Y/W, and ΔP (pressure difference between atmospheric pressure and the pressure under the jet) achieved the best performance in the GPR method with values of R=0.9222, DC=0.8644, and RMSE=0.914. In the SVM, the same model with values of 0.87, 0.7543, and 0.123 for R, DC, and RMSE, respectively, was selected as the superior model.

In this study the effect of chute bed roughness height on energy dissipation has been investigated. First effective parameters were identified and then a general dimensionless relationship was developed. A series of tests were conducted by a physical model using the bed slopes of 25 and 35 degrees and four different uniform roughness heights (3. 38, 7, 12. 7 and 38. 1 mm) having uniform particle sizes on the bed. Total of 80 tests were conducted with flow discharges range between 4 and 40 L s-1 and Froude number between 4. 5 and 9. A relationship was developed for prediction of energy slope on this type roughened bed chutes and the results obtained were compared with the results of previous works. Energy dissipation per unit length of the roughened chute was 7 to 38% greater than that of the smooth chute (without roughness).

One of the most effective strategies for energy dissipation of hydraulic structures is hydraulic jump. The position of hydraulic jump play an important role in design of stilling basin. In this study, hydraulic jump in ogee spillways were simulated by using fluent software. The governing equations were solved through finite volume method and the standard model was applied for estimating the turbulence flow. The equations were discretized in structured mesh accommodate the well-defined boundaries and the volume of fluid (VOF) method was introduced to solve the complex free-surface problem. The study examined the effect of increasing the discharge and the slope on the hydraulic jump position and lentgh. the results suggest that increasing the slope and discharge caused the spatial delay in hydraulic jump. It was found that in ogee spillway with a constant slope, the hydraulic jump length increases up to 120% when the discharge increases. Additionally, for a certain discharge and a constant length of spillway, increasing the slope of spillway decreases the hydraulic jump length up to 43%.

Construction of stilling basins downstream of hydraulic structures is a common tool to dissipate the excess energy created by exit supercritical flows from the outlets. The length of the stilling basin and its construction costs are the factors which should closely be considered by designers to select the most economical structure. Saint Anthony Fall (SAF) stilling basin is one of the compact and short length pools which are utilized in downstream of high velocity exit flows. The efficiency of energy dissipation of this type of stilling basins would be too high despite to the short length of the pool which is the consequence of appurtenances encountered with this basin. Generally, to design this stilling pools the average flow characteristics (such as mean velocity, hydrostatic pressure ,...) are used which reflects some uncertainties due to presence of high turbulent and fluctuating flow in the reach which is to be considered for careful clarifications. In this research a stilling basin of SAF type has been constructed in a glass walled flume and electronic devices been used to take the precise measurements of actual pressure prevailed around the chute blocks of the basin. The results showed that the mean pressure is not in accordance with hydrostatic distribution and varies inversely with entering supercritical flow and directly with submergence ratio of hydraulic jump formed in the basin. It was also revealed that the variation of mean pressure at different faces of the chute blocks follows a different trend at each face.

This study investigates the hydraulic characteristics of flow, including flow velocity, pressure, and cavitation index, at various inflow rates using FLOW-3D. The results indicate that as flow passes over the ogee spillway, the flow velocity increases, and this upward trend continues gradually along the chute section. Due to the steep slope of the chute section, the maximum flow velocity occurs here and is eventually dissipated upon entering the stilling basin, where dynamic energy is absorbed. Longitudinal pressure distribution along the spillway reveals a reduction in pressure from upstream to downstream, with the most significant decrease occurring at the downstream end of the chute. The maximum flow velocities at inflow rates of 300 (minimum design discharge), 830 (10, 000-year flood discharge), and 2270 m³/s (maximum probable flood, P. M. F. ) were recorded as 34. 25, 41. 80, and 44. 90 m/s, respectively, at the downstream end of the chute. Additionally, the minimum flow pressures for these discharge rates were 1. 23, 1. 52, and-5. 9 kPa, respectively. Examination of the cavitation index along the channel bed indicated that cavitation occurs in the chute section under all inflow conditions. However, the cavitation index assessment on the sidewalls showed that the ogee, chute, and initial sections of the chute sidewalls remain unaffected by cavitation. Conversely, the cavitation index in the downstream chute sections decreases below the critical threshold, indicating potential cavitation risk in these regions. Therefore, to prevent the occurrence of the destructive cavitation phenomenon, the implement of flow aeration method from the floor and sidewalls of the channel is recommended.

Comparison of Hydraulic Behavior of Flow over Stepped Spillway and Chute SpillwayExtended AbstractBackground and Objectives Stepped spillways are convenient and economical options for high dams compared to other types of spillways because of their special abilities such as construction procedure compatibility with the Roller Compacted Concrete Dams (RCC Dam) technology, the ability of self-aeration of flow and reduction the stilling basin dimensions at the downstream dam toe due to significant energy dissipation. Depending on the discharge rate, step height and slope, three flow regimes can be identified on stepped spillways: nappe, transition, and skimming flow. Nappe flow occurs for relatively low discharge rates and lower slopes. Transition flow with a range of intermediate flow rates has a chaotic flow motion with intense splashing. Skimming flow occurs for relatively higher discharge rates and steeper slopes, is characterized by a flow over the pseudo-bottom formed by small vortices between steps. On a stepped spillway, the steps act as macro roughness elements, contributing to enhanced energy dissipation and significant aeration. In a skimming flow, the upstream flow motion is nonaerated, and the free surface appears smooth and glossy up to the inception point of free-surface aeration. In this developing flow region, a turbulent boundary layer grows until the outer edge of the boundary layer interacts with the free surface and air entrainment takes place. In recent decades, much research has been done on various flow regimes over the stepped spillway, the way they dissipate energy and the impact of the geometry of the steps on flow structure. In this research, hydraulic performance of skimming flow over Zhaveh stepped spillway has been studied and qualitative and quantitative comparison of flow between stepped and chute spillways has been presented.Methodology A 2D numerical models of spillway has prepared using FLUENT 6.3.26 software, k-e RNG turbulence model and Mixture multiphase flow method to simulate and calculate the hydraulic characteristics of the energy dissipation of spillways. The softwares to create the spillways geometry and mesh were SOLIDWORKS and GAMBIT respectively. The meshes in the tank section were quadrilateral and due to irregular geometry and the presence of stairs, meshes in the spillway and chute section were tri / pave. The boundary conditions were velocity inlet for inlet flow, free pressure inlet for free surface flow, outlet pressure for outflow and wall for floor and stairs. The numerical model has been calibrated applying experimental data extracted from the physical model of the Zhaveh spillway. It is stepped spillway with a height of 85 m and located on the Zaveh river at the junction of the Gavrood and Gheshlagh rivers at 35 km south of Sanandaj city. The spillway with a crest length of 55 m and a side slope of 1.2V:1H (50.19 degrees) located on the body of the Zhaveh dam. Findings The results indicated in addition to agreement between laboratory and numerical data, having steps alongside the chute spillway can reduce significantly the length of the boundary layer which is developed from the spillway crest and encountered with the flow surface from where the flow air entrainment is initiated. So the inception point related to air entrainment is located further upstream. Analysing the flow pattern indicated that due to aeration after the inception point, the flow depth and velocity in stepped spillway increases and decreases respectively compared to a chute spillway. Flow aeration causes the cavitation index to become much higher than the critical value (0.2) in the entire stepped spillway thus the risk of cavitation occurrence and the relevant damages are reduced considerably. While it was observed that the possibility of cavitation occurrence was high on the chute spillway (without steps) starting from 56 m downstream of the spillway crest. As a result, cavitation erosion was more likely expected on the chute spillway surface. Also for design discharge, the flow energy was effectively dissipated alongside the stepped spillway in comparison to chute spillway with a discrepancy of 46%.Conclusion The application of the stepped spillway would be more appropriate and economical than the chute spillway due to the various advantages mentioned above and also there is no risk of cavitation on the Zaveh stepped spillway, while in the end of the chute spillway Corresponding to it, we may encounter cavitation erosion.

In this study the effect of chute bed roughness height on energy dissipation has been investigated. To do so first general non dimensional relationship was developed. Then series of experimental tests were conducted in a physical model using three different bed slopes (15, 22.5 and 30 degrees) and three different uniform roughness heights (1.1, 1.43 and 2.1 cm). Total of 48 tests were conducted with flow discharges ranged between 15 and 45 lit/sec. Results show that in comparison with the smooth bed, nearly 12 to 48 percent of the flow energy was dissipated on the roughened bed chute. Maximum energy dissipation occurred for slope of 22.5 degrees and the minimum energy was dissipated on 30 degrees chute. A relationship was developed for prediction of energy slope on this type roughened bed chutes and the results obtained were compared with the results of previous works.

As a method for dimension reduction and elimination of energy damper structures that are located downstream of rapids, obstacles that are put on rapids are sometimes employed. In this research, damping capabilities of floating cubic obstacles were investigated using an experimental model. To do this, various experiments were performed on four different slopes of rapids with and without obstacles in a laboratory open channel in the hydraulic laboratory of Shahid Chamran University of Ahvaz. Results of the experiments without obstacles on discharges contained in this research’ s scope showed that the amount of damped energy relative to the upstream energy ranges from 10 percent for a slope of 1: 4 to 63 percent for a slope of 1: 5. According to comparison of energy loss in different slopes, we can conclude that the reduction of chute bed slope increases the relative damped energy. We can also argue that the reduced chute bed slope leads to a slower energy loss procedure. Energy dissipation had an increase of 17 to 44 percent according to the studied results of models with and without obstacles. According to comparison of energy loss in different slopes of models with obstacles, we can conclude that the amount of relative damped energy increases and the damped energy reduction occurs on lower slope by reducing the chute bed slope. Using multi-variable regression, some equations were extracted in the final section in order to predict energy damping in such rapids with or without obstacles.