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.

Introduction: In Water regulation and distribution structures are the main components of any irrigation network. If these structures fail, it has a direct impact on the network performance and water loss. The type and shape of the regulation structure can be effective for better performance of the distribution structure. Studies show that one of the problems in the irrigation networks is due to the mechanism of existing structures. At the present, regulation structures with various shapes are used in the world. Rubicon Water has been working in Australia since 1995 to develop, build and install water regulation and distribution structures. The automated regulation structure of the company, called FlumeGate, has been installed in different countries such as Australia, India, China and the United States. In the present study, the variable height whirling-VHW weir was introduced, designed, and constructed inspired by FlumeGate. The shape, mechanism and installation of this weir are relatively simple. The energy required to change its position is less than other gates. This is an overshot structure that has a better performance in the face of floating objects. Placing the weir crest at different heights is another advantage over the fixed weirs. By determining the stage-discharge relationship at different angles, it can also be used as a flow measurement structure. The purpose of this study is to determine the stage-discharge relationship of the structure and its discharge coefficient at different openings. Methodology: The body of variable height whirling weir consists of two quarter circle sections on both sides and a rectangular section on the floor. At full opening, the rectangular section is placed horizontally and provides the maximum cross-sectional area for flow. By whirling the body, this structure acts like a weir and, while regulating the water level, also passes a specified discharge. A flume with a trapezoidal section with a length of 60. 5 m was used to investigate the hydraulic behavior of VHW weir. The bottom width of this flume is 0. 3 meters, the maximum depth is 0. 25 meters, the side slope is 1: 1 and the average slope is 0. 0009. The VHW weir was installed at a distance of 44. 5 meters from the beginning of the canal to create a uniform flow. To collect the required data, different weir openings were investigated in each specified discharge. Data including discharge, upstream water level of weir and angle of weir floor relative to the horizon were recorded. At each stage of the experiment, discharge was recorded by a flowmeter for two minutes and piezometer board was captured via digital photography. The recorded photos were digitized by Grapher software and the water depth in the all piezometers was determined. For determining the stage-discharge relationship of this structure in free flow condition, hydraulic, power and dimensional analysis methods were used. Results and Discussion: In the hydraulic method, stage-discharge rating curves were plotted by the upstream water depth of the VHW weir and inlet discharge to the canal at different angles. Then, the discharge coefficient was determined for each opening. By obtaining the discharge coefficient for each opening, a relation can be written for the changes of the discharge coefficient versus the angle. Considering the relationship between the discharge coefficient and the angle, it can be seen that for angles larger than 35 degree, the VHW weir had a different performance compared to the smaller angles. The reason for changing the data trend can be attributed to increase the effect of the weir wall on the flow. In the power method by having the upstream water depth of the VHW weir and the inlet discharge to the canal, it is also possible to obtain a relation for the coefficient C and b versus the angle. In this method, the relationship trend changes at angle of 30 degrees. To generalize the results, the two dimensionless parameters which obtained from Buckingham theorem were plotted. According to the graph and the data trend, the stage-discharge relationship can be divided into two parts. Data up to an angle of 35 degrees follows a trend, so it is rational to use from one relation for angle of 7 to 35 degrees and another relation for angle of 35 to 50 degrees. Based on the statistical parameters, the obtained relationships based on the dimensional analysis gave a better result. Conclusion: discharge of VHW weir was obtained by three methods: hydraulic, power and dimensional analysis. Comparison of the statistical parameters of these three methods shows that the relationship obtained from the dimensional analysis is almost consistent with the data. The results show that the hydraulic behavior of the weir at angles larger than 35 degrees is different from smaller angles. The main reason for this difference is the effect of the structure body on the flow path.

Problems related to sedimentation and depositions can be minimized by using a system where weirs and gate are combined in open canals while the floated materials run over and sediments run under the structure. Because of effect of overflow on underflow, the variation rate of discharge coefficient with geometric and hydraulic parameters is different with their use each other separately. It is important for cylindrical weir-gate because the flow nape will sit on the weir completely the current work describes the results of experimental investigation on effect of weir flow on gate discharge coefficient for cylindrical weir-gate. In this way the gate discharge is measured against upstream water depth in two condition of weir flow and without weir flow. The experiments are carried out in a laboratory flume 10 m length, 60 cm wide and 70 cm height. Results indicate that increasing dimensionless parameters of Hw/a and Hw/D cause decreasing the discharge coefficient for weir flow and it rises about 1-25% without weir flow. For a constant values of the Hw/a increasing the gate height, the effect of weir on gate discharge coefficient decreases for the cylindrical weir-gate.

The self-excited oscillating cavitation jet nozzle (SEOCJN) serves as a crucial component for converting hydrostatic energy into dynamic pressure energy and ensuring optimal hydraulic and cavitation performance of cavitating jets. Thus, it is of crucial significance to understand the cavitation characteristics and the influence law of SEOCJN for its extensive industrial applications. This paper utilizes numerical simulation methods to analyze the dynamic process of cavitation initiation, development, and outlet cavitation performance of SEOCJN. It explores the effects of inlet pressure and flow rate on the frequency characteristics of SEOCJN, and establishes a mathematical relationship between self-excited oscillation frequency and outlet flow frequency. The results indicate that the self-excited oscillation nozzle has an inlet diameter (D1) of 4. 7 mm, an outlet diameter (D2) of 12. 2 mm, a length (L) of 52 mm, a chamber diameter (D) of 83 mm, an oscillation angle of 120°, and an inlet pressure (Pin) of 4. 8 MPa. At these parameters, the frequency of the pulse jet reaches 830. 01 Hz, with an internal flow period of approximately 0. 0024 s. The maximum vapor volume fraction is found to be located 0. 28 m from the outlet of the SEOCJN. Furthermore, the frequency of self-excited oscillation pulse increases with an increase in inlet pressure. These findings provide a theoretical basis for the industrial application of self-excited oscillation cavitation jet nozzles

Introduction: Side weir structures are extensively used in hydraulic engineering, irrigation and environmental engineering, and it usually consists of a main weir and a lateral channel. Side weirs are also used as an emergency structure. This structure is installed on one side or both sides of the main channel to divert the flow from the main channel to the side channel. Lateral outflow takes place when the water surface in the main channel rises above the weir sill. Flow over a side weir is a typical case of spatially varied flow with decreasing discharge. There have been extensive studies on side weir overflows. Most of the previous theoretical an alysisand experimental research works are related to the flow over rectangular side weirs in rectangular main channels. In the current study, the flow conditions over a trapezoidal side weir located in a rectangular main channel in subcritical flow regime is considered.Materials and Methods: The experiments were performed in a rectangular open channel having provisionsfor a side weir at one side of the channel. The main channel was horizontal with 12 m length, 0.25 m width, and0.5 m height, and it was installed on a frame; lateral channel that has a length of 6 m, width of 0.25 m, and height of 1 m. It was set up parallel to the main channel; walls and its bed were made up of Plexiglas plates. The sideweir was positioned at a distance of 6 m from the channel’s entrance. A total of 121 experiments on trapezoidalside weirs were carried out.Results and Discussion: For trapezoidal side weir, effective non-dimensionnal parameters were identified using dimensional analysis and Buckingham's Pi-Theorem. Finally, the following non-dimensional parameters were considered as the most effective ones on the discharge coefficient of the trapezoidal side weir flow. Cd=f “Fr1, p/y1/T/y1, z” in which Fr1=upstream Froude number, P=hight of the trapezoidal side weir, y1=upstream water depth, z=side slope of the trapezoidal side weir and T=top flow width of the trapezoidal side weir. Water surfaceprofiles were measured along the weir crest, the main channel centerline, and far from the weir section. Different elevations in water surface profile depend on the upstream Froude number in the main channel; depth differences in low Froude numbers are at minimum values, and in high Froude numbers are at maximum amounts. The water surface level along the crest drops at the entrance of the side weir to the first half of the side weir; and it has been attributed to the side weir entrance effect at the upstream. Afterwards, the water level rises towards the downstream of the weir. According to the experimental results, measurements of the water in the centerline of the main channel are reliable and water surface drop is negligible. According to the parameters affecting the discharge coefficient for each value of z, discharge coefficient equations were developed with accept able accuracy such that the effects of this parameter were shown separately. Finally, the general equation was proposed. The general functional form for discharge coefficient is presented as follows where the effect of the side slope parameter, z, is also considered. Cd=0.085 Fr13.16-0.053(b/T)1.4-0.032(P/y1)1.04+0.18(z/1+z)1.09+0.55 The mean and maximum percentage errors of the discharge coefficient computed using the proposed equation are as 2.6% and 11.5%, respectively.Conclusion: In this study, the characteristics of trapezoidal side weir overflows in subcritical flow regime were discussed. For this purpose, experimental data related to the water surface profile of the side weir and discharge coefficient were collected and analyzed. The results showed that the most efficient section form easuring water surface profile is located at the center line of the main channel. It was found that for trapezoidalside weir, the discharge coefficient depends on the Froude number, the ratio of crest height to initial depth, the over flow length to initial depth, and the side slope of the weir. In this study, conventional trapezoidal weir the oryhas been used in order to evaluate the discharge coefficient and provide side weir discharge equation. For this purpose, three reference depths were considered for conventional weir, and for each depth an equation was developed for the discharge coefficient. Comparison between predicted values and experimental data showed that average flow depth results in accurate outcomes for assessing the discharge coefficient. The average value of error for discharge coefficient estimation by the proposed equation is 2.6%. Thus this equation is proposed foruse in practice by water engineers.

Cavitation phenomenon can cause deterioration of the hydraulic performance, damage by pitting, material erosion, structure vibration and noise in fluid machinery, turbo-machinery, ship propellers and in many other applications. Therefore, it is important to detect inception of cavitation phenomenon. An experimental study has been carried out in order to investigate the noise radiated by various cavitating sources to determine the validity of noise measurements for detecting the onset of cavitation. Measurements have been made measuring the noise radiated by a number of configurations in a water tunnel at various operating condition to determine the onset of cavitation. The measurements have been conducted over a frequency range of 31. 5 Hz to 31. 5 kHz in one-third octave bands. The onset of cavitation was measured visually through a Perspex side of the working section of the water tunnel. Moreover, a theoretical estimate of the pressure radiated from the cavitation nuclei at their critical radii and their frequency was presented. Tests indicated that, generally, at the point of visual inception there was a marked rise of the sound pressure level in the high-frequency noise, whilst the low-frequency noise increased as the cavitation developed. This finding was supported by the theoretical estimate of the pulsating frequency of cavitation nuclei. The results illustrated that the visual observations of inception confirm the noise measurements.

In this paper, the hydraulic characteristics of a sharp crested triangular side weir have been experimentally studied. It was found that the DeMarchi coefficient of discharge for a sharp crested triangular side weir in subcritical flow is related to the main channel Froude number, the apex angle of weir and ratio of weir height to upstream depth of flow. Suitable equations for discharge coefficient are also obtained.

Introduction: Cavitation is one of the most important problems that may occur due to high flow velocity in dam spillways. In order to predict of dam spillway structure during operation, Azad dam spillway hydraulic model has been modeled in Tehran Water Research Institute. Materials and Methods: In this study, using computational fluid dynamics in the form of a finite volume method used in ANSYS FLUENT software, flow modeling in these channels, and a fluid volume model (VOF) in a three-dimensional state, including two-phase flow of water and air, used for Considering current turbulence, k-ε,model has been used. In order to confirm the results of the model, a comparison was made with the results of a hydraulic model implemented without the aero-damping system of Azad spillway. Findings: Then, in order to confirm the location and number of aeration systems, two scenarios (two and three aeration systems) including step ramp (RAMP) on the floor and the wall of the duct with a suitable slope and the installation of the aeration slot in the wall have been used, which sends air near the floor And the walls will be. Conclusion: Then, by checking flow parameters such as speed, pressure and cavitation index, overflow with two aeration systems was confirmed as the best option.

The flow characteristics of triangular weir are studied under free and submerged flow condition. This paper reports the results of an investigation carried out to establish the stagedischarge relationship for sharp and broad crested triangular weir. The stage-discharge relationships are deduced by the application of the TC -theorem of the dimensional analysis and the incomplete self-similarity theory coupled with experimental data.