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.

SPILLWAYs are one of the Most Important Hydraulic Structures of Dams that Transmitted Flood Entering the Reservoir with Sufficient Safety when Capacity Reservoir Completed. To Reduce the Cost of long SPILLWAYs and Topographic Factors, Walls, Especially in the Chutes Constructed. In this study, FLOW over the Gavshan Dam SPILLWAY Comprising Approach Channels, Ogee Crest, Converging Chute and Flip Bucket using FLOW 3d Software and Turbulence Model K-, Simulated and Hydraulic Characteristics of FLOW such as the Distribution of Velocity, Pressure, and Changes in the Depth is Studied. Comparing Numerical Results with Experimental Model Showed that there is not much difference between them. Changes in FLOW velocity over a SPILLWAY crest increase sudden and Rapidly and this Process Followed along Chute as far as most FLOW Velocity Rate in 1350 Cubic Meters per second, Equivalent to 30 meters per Seconds Accurate at the End of Chute (start of Flip Buckets). 2/07 Degree Angle Convergent Walls are Optimized Angle to Prevent the Formation of Transverse Waves and Need to Increase the Height of the Walls of the Convergent SPILLWAY.

Stepped SPILLWAYs are technically and economically regarded as one of the most efficient options for energy dissipation of SPILLWAY FLOWs. A remarkable amount of the FLOW energy is dissipated due to the hydraulic resistance of rough elements or those steps. Therefore, the energy dissipation obviates the need to build an energy dissipation system at the end of the downstream and reduces its size to a large extent. Considering the mentioned point and the required technology to use RCC in building such SPILLWAYs, it is indispensable to thoroughly examine the hydraulic processes and the FLOWs passing through them. The FLOWs passing through the stepped SPILLWAYs are divided into three types of nappe, transition, and skimming. Most studies concerned with stepped SPILLWAYs have focused on nappe and skimming FLOWs, while transition FLOWs have not been fully addressed. Moreover, most of the stepped SPILLWAYs’ designs have been based on nappe and skimming FLOWs types. Therefore, the present study employed laboratory methods to examine the FLOW formation in transition mode in order to determine the upper and lower limit of the transition FLOW regime, and finally, provides more space for studying its characteristics. The FLOW regimes’ type depends on the step discharge and geometrical shape. Due to variations in the depth and velocity of FLOW, air concentration and energy dissipation in the three different regimes, it is essential to evaluate the FLOW in the regimes. Thus, the FLOW regimes’ onset has been the subject of many laboratory studies. The previous experiments and studies have shown that the nappe FLOW onset is a function of the height and length of step and also, the critical depth. This research was conducted in Water Research Center of Power Administration in order to determine the range of transition FLOW regime and hydraulic parameters of various FLOW regimes, including dynamic pressure at the steps’ bottom and the depth of FLOW passing over the steps as a FLOW profile. To do so, SPILLWAYs’ models of Siahbisheh dams were used, which were constructed with the scale of 1: 15 and 1: 20. The FLOW will be fully developed, after passing through the SPILLWAY crest and the aeration inception point. The upper and lower limits of the transition FLOW regime were determined by letting different discharges pass over the SPILLWAYs. To detect the nappe FLOWs’ entrance into the transition FLOWs, i. e. the lower limit of transition FLOW regime, the inception of water spray can be used. The water spray level will be higher in sloped SPILLWAYs. Moreover, the FLOW jet has more fluctuations in the transition FLOW regimes of pool; in other words, it will be in immersion mode. In addition, some FLOW rotation works can be noticed. The criterion for determining the threshold for the onset of skimming FLOW, i. e. the upper limit of transition FLOW, is the FLOW slipping from the edge of one step onto the next. It is worth mentioning that existence or lack of air holes does not play any role in proving this. This is in contrast to Chanson’ s theory; however, it is in line with Chamani and Rajaratnam’ s view. The onset of FLOW rotation in the pool below the step was also taken into account; these rotations are not still complete enough to enter the skimming FLOW section. After determining the FLOW regimes, the dynamic pressure and profile of passing FLOW were measured in transition regimes. In order to measure the pressure exerted on the steps’ bottom, 3 piezometers at (y/l), which are equal to 0. 14, 0. 45, and 0. 71, were installed on four SPILLWAYs. Transducer system adapters, computer systems and an information processing software were used in order to measure the dynamic pressure moment-by-moment. The pressure sensors used in the experiment were 0. 150 kg/〖 Cm〗 ^2 (150 mbar). The pressure fluctuations in each piezometer were recorded during 30 seconds with the frequency of 100 hertz. To measure the FLOW profile, without accounting for water spray, a point gauge was used. The results of the study revealed that the increase in the SPILLWAY slope reduces the area for occurrence of transition FLOW regime. Moreover, as the ratio of h/l increase the ratio of y_c/h decreases, which shows faster formation of a skimming FLOW. In the nappe FLOW regime, it is noticed that pressure increases from the step bottom to the edge, where it moves with a slight slope to the middle of the step and then, continues with a steep slope. In the nappe FLOW regime, increasing the SPILLWAY slope, increases the pressure from the step bottom toward the edge. Moreover, the maximum and minimum pressures occur near the step edge. With respect to the transition FLOW regime, the pressure remains almost constant from the step bottom up to y/l=0. 4 and then continues with a steep slope toward the step edge. In addition, in the transition FLOW regime, the maximum and minimum pressures occur on the step edge. In the skimming FLOW regime, the mean pressure increases from the step bottom toward theedge. This increasing trend has a direct influence on the SPILLWAY slope. The maximum pressure occurs in the middle of the step and then decreases with a slight slope. Similarly, the minimum pressure occurs in the middle of the step and then, increases toward the step edge. Finally, in the skimming FLOW regime, increasing the SPILLWAY slope is followed by a decrease in the maximum pressure.

One of the important issues in the design of chute SPILLWAY is to study the FLOW characteristics in the chute path because the FLOW is supercritical. In this study, the hydraulic characteristic of FLOW in the chute SPILLWAY of Surk dam has been investigated using both physical and numerical modeling. The plexiglass physical model was made with a geometry scale of 1: 50 and FLUENT software was used for mathematical modeling. The experiments were carried out at 5 different discharges and the parameters of pressure, velocity and depth of FLOW were measured in the central axis and at the side of the wall. The results showed that among the measured parameters of FLUENT model, the velocity parameter was simulated with the lowest average error rate (4. 3%) and the depth parameter with the highest average error rate (16. 9%). Also, the Nash-Sutcliff coefficient and the correlation coefficient for the parameters, indicated that FLUENT software has a good ability to simulate FLOW characteristics over the chute SPILLWAY with a suddenly change slope. Regarding the RMSE and NRMSE criteria, FLUENT model have had the highest accuracy in calculating the FLOW parameters by using finite volume numerical method, turbulent model k- , RNG, SIMPLE pressure correction method and VOF two-phase method.

When the dam reservoir exceeds its capacity, the SPILLWAY, as one of the most significant water-dependent elements of dams, safely conveys the oncoming flood FLOW to the dam reservoir. Dam safety is inextricably linked to sufficient SPILLWAY capacity. Therefore, one of the most pressing issues in all dams is ensuring the accuracy of structures and the hydraulic operation of SPILLWAYs. In the present study, the hydraulic parameters of the FLOW on the SPILLWAY for the flood discharges with 50 and 10,000-year return periods were simulated using WS77 and FLOW3D softwares in order to evaluate the factors affecting the destruction of the concrete panel of the Bukan Dam SPILLWAY. Various known factors in the destruction of SPILLWAY floor concrete panels such as cavitation, pressure fluctuations, uplift pressure and hydraulic jacks were also investigated. As shown in the results, the minimum cavitation index in selected floods of 50 and 10 thousand years is 0.31 and 0.275, respectively, which is more than the critical value of 0.2. Furthermore, at the maximum values estimated in the two floods, the failure potential index is 111 and 198 (2.5 cm offset) respectively, which is much below the value of the destruction threshold of 500. However, the results show that increased pressure owing to the hydraulic jack phenomenon, as well as uplift pressure to values greater than the concrete panel weight component and anchor strength, has resulted in SPILLWAY floor concrete panel displacement.

Stepped ogee SPILLWAYs are one of the most widely used types of dams that are used in most dam construction projects, including small and large dams. The inception point of aeration on these SPILLWAYs is an important place in determining the range of single-phase and two-phase FLOW, which characterize the areas at risk of cavitation. In this paper, the effect of roughness on the location of the inception point of FLOW aeration (IPFA) on the stepped Ogee SPILLWAYs was investigated. For this purpose, the surface of the steps of a laboratory model was covered with gravel with specific granulation. The result indicated that by roughing the surface of steps, the displacement of IPFA moves towards the crest (upstream) and the length of non-aerated area on the stepped SPILLWAYs is decreased by about 15 percent. The results declared that there is a direct exponentially relation between FLOW rate and displacement IPFA. At low FLOW rates, most of the FLOW turbulence is due to the roughness created by the geometry of the steps, hence the role of surface roughness is negligible, while with increasing FLOW rate, its role in increasing the FLOW turbulence increases, and its effect on displacement of IPFA becomes obvious. At a given FLOW, the length of the non-aerated is decreased with increasing roughness.In this study, the effect of surface roughness of steps on the displacement of IFPA was investigated experimentally. To this end number of laboratory experiments were programmed. To investigate the objective of this study, a stepped ogee SPILLWAY in which its horizontal part of steps was covered by gravel with given grain size. The results declared that three factors including the FLOW rate, the roughness caused by steps dimension (ks), and the roughness of steps surface (ns) are effective in the displacement of IPFA. In this study, the change in the size of the steps and the longitudinal slope of the stepped chute on the displacement of IPFA has not been investigated because it has already been studied by other researchers. There is a direct exponential relationship between the discharge and the IPFA (length of the non-aerated area on the stepped ogee SPILLWAY). As the FLOW rate increases, the location of this point is transferred downstream exponentially. With the increase of FLOW, the role of roughness in IPFA displacement became clearer and the reason is the increase of its role in creating and increasing FLOW turbulence. On average, surface roughness can be about 15% effective in reducing the displacement of IPFA.

SPILLWAYs are used in dam projects to convey flood FLOWs and prevent destructive damages of downstream hydraulic systems, while the construction of other types of SPILLWAYs is restricted, or there is a need to pass great values of flood discharge with a limited head. Siphon SPILLWAY is a kind of dam SPILLWAYs employed in a number of dam reservoirs. This SPILLWAY is applied while the space for constructing other types of SPILLWAYs is restricted, or when there is a need to pass great values of ood discharge with a limited head. One of the most important defects of this SPILLWAY is a complicated uid-structure interaction due to the establishment of di erent ow regimes inside the SPILLWAY. This situation becomes more complicated when the SPILLWAY is not connected to the dam, working individually. Despite the importance of the operation of these hydraulic structures, there is a lack of comprehensive research to investigate the hydraulic behavior of these structures and the ow  eld around and inside them. In the present study, di erent unsteady ow regimes including sub-atmospheric ow, two-phase ow, and black-water ow and their e ects on the hydraulic characteristics of siphon SPILLWAYs were investigated. For this purpose, ANSYS CFX software was applied to simulate the ow  eld in such SPILLWAYs. To validate the obtained ow regimes, via numerical modeling, experimental results of the former studies were used. Results indicated that the pressure fluctuations were mostly greater beneath the inlet and throat of the SPILLWAY compared to the other sections.

In this study, numerical simulation of FLOW over a chute SPILLWAY is presented using the computational fluid dynamics (CFD) method. The FLOW characteristics such as velocity, pressure and depth through the SPILLWAY have been calculated for four different FLOW rates. Since the actual FLOW is turbulent, the RNG turbulence model has been used for simulation. The numerical computed results of piezometric pressure and FLOW velocity along the SPILLWAY were compared with the results from the hydraulic model tests. The maximum difference between calculated and experiment results in average velocity values was 5.47% and in piezometric pressure values was 7.97%, and the numerical results agreed well with experiments.

 The element-free Galerkin method (EFG) and the natural element method (NEM) are two well know methods in the computational mechanics and meshless methods. In this paper, a computational scheme using a variable domain and a fixed domain is presented based on coupling of EFG and NEM for analysis of two dimensional SPILLWAY FLOW under radial gate for the computation of the free surface profile and the FLOW rate of a 2D gravity fluid f low through a conduit and under a radial gate. The coupling between EFG and NE is achieved by using the natural element shape functions as the weight functions for the element free Galerkin method. In this method, contrary to EFG method, the imposition of the essential boundary conditions is straight forward and shape functions fulfill the Kronecker delta property. In this study, the fluid is assumed to be inviscid and incompressible. The validity of the proposed method is verified by comparing the results from EFG-NE simulation results with those obtained from finite element simulation and experimental results. It is concluded that the results obtained by EFG-NE method is in good agreement with those from FEM and experimental results. Therefore, the coupled EFG-NE method is capable to handle SPILLWAY FLOW simulation.

Using stepped SPILLWAY due to its low cost and high efficiency is increasingly on the rise. Hence, the studies in this area are associated with the growth and attention from dam engineers but most of these studies were including stepped SPILLWAY with uniform step height while the non-uniform step heights can also be considered as an option in some cases. In this study, a physical model of Herat dam for stepped SPILLWAY with 1.3 m height and a slope of 19.2o were used for the verification of numerical models then, three types of stepped configurations using computational fluid dynamics in ANSYS CFX software for range of 1.54#dc/h # 16.15 tested. Two-phase FLOW simulation for each configuration and all of the discharge took place and results in the case of FLOW pattern, energy dissipation and aeration point were compared. The results showed minimum difference in energy dissipation for nappe regime FLOW and maximum difference for skimming regime FLOW.