One of the most effective and economic methods for prevention of damages due to cavitation is flow aerating. Aerators are structures which are constructed on spillways for aerating pursposes. Mechanism of air-entraining to the water flow is qiute complex and for designing of aerators, physical model is usually used.In this paper, it is shown the contact angle of water jet to the spillway bed, has an important effect on aerating rate. Due to the high impoartance of physical models on the design of aeration, scaled errors are sdiscussed and a techniquebased on roughening of model in order to reducing the scaled errors is proposed.

Soil aeration by imported machines were reportedly unsatisfactory due to creation of shallow holes, taking off some patches of the turf and time consuming work needed for collecting the excavated cores. Considering these problems, a machine was developed to suit Iran’ s lawn spaces. To develop an appropriate aerator, the shape of the plugs was studied at the first step and for this purpose six types of plugs with conical and cylindrical cross section (with and without slot) with tips cut diagonally and perpendicularly were built. The plugs were compared in an experiment based on complete randomized blocks design with 3 replication in an urban lawn space with clay soil in terms of the required static force for cutting the thatch and penetrating to the soil as well as the length of projected cores. The results showed that the conical plugs with beveled tips had a 28 millimeter longer cores than the cylindrical plugs with similar tip using approximately equal forces for insertion. Having chosen the appropriate shape of plug, a split roller with a relatively large diameter were constructed for installing plugs around it and the whole device attached to a walking tractor. Comparing the developed machine with a commercial self-propelled aerator revealed that the developed aerator improved the length of the cores and depth of the holes. The split roller in the machine which windrowed the cores also caused a 65% decrease in labor requirement for collecting the cores and did not have dug patches of turf.

Dam Weirs are used to regulate the water level. About 33 percent of dam failures have occurred due to insufficient capacity of weirs. One way to prevent is to use weir with nonlinear crest, such as labyrinth weir. In this study, the effect of dentate and orifice as well as a combination of both in the weir and in three magnification ratios of 2, 3 and 4 were investigated. The experiments were performed in a rectangular laboratory channel 15 meters long, 0. 8 meters wide and 1 meter high with a flow rate of 10 to 90 liters per second. Nine physical models of weirs were used in this study, which were 3 mm thick, 15 cm high and 40, 60 and 80 cm long. Also, quarter cylinders with a radius of 1. 5 cm were installed as aerators on the simple weir models. The results showed that aerators increase the discharge coefficient up to 13% compared to simple labyrinth weir. But with the increase in flow as well as the magnification of the labyrinth weir, this effect will be very small. Studies showed for L/W= 2 and H/P= 0. 2, the discharge coefficient of orifice-dentate weir and dentate weir are 75. 6 and 17. 5 percent, respectively, more than the simple labyrinth weir. However, dent and orifice may lose their efficiency in high heads and the discharge coefficient will be close to simple labyrinth weir. The reason for these changes is the flow interference in downstream of weir which will be more by creating dentate and orifices. Also, increasing the magnification of labyrinth weir reduces the discharge coefficient, but this reduction in orifice-dentate labyrinth weir is much greater than the other two types of weirs and reaches up to 40%. Therefore, the orifice-dentate labyrinth weir performance at high magnification ratios does not seem appropriate.

Cavitation is one of the most common and destructive causes of spillways and water conveyance tunnels. One of the most effective ways to prevent the cavitation is to aerate the current, provide the pressure and prevent excessive suction. The longer is the separation length downstream of the air entrance to flow, the more efficiency of cavitator. Conventional types of aerators (cavitators) in hydraulic structures including ramps, steps, grooves, and their combinations. In this research, the performance of 19 cavitators with different geometries in a pressurized flow inside a box tunnel, for 5 discharges with/without aeration were investigated. All experiments were performed for 3 times to validate the experimental results and reduce the experimental errors. Statistical analysis of the experimental results showed that the type of cavitator had considerable effects on the separation length. In spite of the positive effects of ramp height and discharge on separation length, the angle of ramp, step height, and groove depth had non-significant effects on separation length. Finally, two combined aerators were proposed, which in practice had better results in comparison with conventional aerators in hydraulic structures.

Serious damages have been reported in hydraulic structures due to cavitation. It is known that introducing air into the flow will considerably reduce cavitation risks. Thus, aerators are used in many situations to introduce air into the flow and to eliminate cavitation tendency. Although many works have been reported for flow aeration in outlet conduits of rectangular sections, less information can be found for circular tunnels. These structures are commonly used to supply water for hydroelectric power plants or drinking and irrigation systems. In this paper, experimental information regarding the intensity of pressure fluctuations and its dominant frequency downstream of rectangular aerators in such structures are provided. Experiments were performed in a circular pipe of 28.8 cm diameter. Rectangular aerators of different heights and angles were fixed inside the tunnel and air was supplied through aerator to check its effect on the intensity of hydrodynamic pressures. This information is useful for the structural design of such outlet tunnels.

Introduction: Local scour is a main factor involved in the destruction of bridge piers in rivers before the life expectancy of these structures. One of the newest indirect methods for reducing the erosion and scour around the bridge piers is the air injection method based on counteracting with a downward flow to create conditions to prevent or reduce the flow impact on the bed and the destruction of bridge piers. Tipireddy and Barkdoll (2019) studied the effect of air injection on controlling bridge pier scour. The results of this study showed that the maximum scour depth decreased with increasing air injection rate until the ratio of air outflow velocity from the pores to flow velocity reached 57. 1 and then increased. Using air injection to reduce bridge pier scour has been explored in only one study, considering all parameters except for the constant air outflow rate. The main objective of this study was to investigate the effect of air injection on reducing bridge pier scour considering the number and the location of injection pipes. Methodology: Experiments were carried out at the Hydraulic Laboratory of the Faculty of Water Engineering, Shahid Chamran University of Ahvaz in a flume 10 m long and 0. 74 m wide and 0. 6 m deep. The bottom of the flume was covered by sediments with a mean diameter of 0. 7 mm with a standard deviation of 1. 21 indicating uniform sand. All experiments were done in four Froude numbers of 0. 18, 0. 2, 0. 22, and 0. 24 at a constant depth of 15 cm under clear-water conditions. To create these conditions, the flow depth was adjusted so that the ratio of flow velocity to the critical velocity could be less than 95%. In order to determine the appropriate time for the experiments, a 12-hour test at a Froude number of 0. 2 was performed and it was observed that about 90% of the scour occurred in the first 3 hours. In order to create an air injection system, porous pipes were selected with an internal diameter of 4 mm. Each pipe had 24 pores with a diameter of 2. 2 mm at fixed intervals mounted on the upstream half of the pier and the two ends were connected to the air compressor for injection. Experiments were carried out at an air injection rate of 100 lit/min and in 7 different numbers and positions of aeration pipes on the pier. The pipes were mounted in three general modes: one pipe, two pipes and three pipes. The installation level of the pipe on the pier was considered at three heights of 1/3h, 1/2h, and 2/3h from the bed. Results and Discussion: A number of four control experiments (without the air injection system) was first performed at four specified Froude numbers. A total number of 28 experiments were performed in the presence of the air injection system at the air injection rate of 100 lit/min. The aeration pipe at the upstream half of the pier provides some protection for the sediments against the horseshoe vortices. Effect of aeration pipe position on scour depth and scour development around bridge pier The transverse expansion of the scour hole for the bridge pier was plotted in two general modes using a single aeration pipe and two aeration pipes in four Froude numbers. In the single-pipe mode, a maximum decrease in the scour hole depth in front of the bridge pier (25. 5%) was observed at a pipe installation depth of 5 cm beneath the bed and for the Froude number of 0. 18. For the use of two pipes with the same injection rate and similar hydraulic conditions, the maximum decrease in scour depth of 11. 8% occurred when the pipes were installed at depths of 7. 5 and 10 cm beneath the bed. Effect of aeration pipe on scour depth in scour development around bridge pier In order to investigate the effect of the number of pipes on the scour depth, the transverse expansion of the scour hole around the bridge pier was plotted in three general modes: single pipe (three mode), two pipes (three modes) and three pipes (one mode). The results showed that a lowest efficiency was observed in the state of the three pipes and the efficiency is in the one state. Effect of Froude Number on Scour Depth and Scour Expansion around Bridge Pier The shape of the relative scour depth was plotted against the Froude number for the use of an aeration pipe. The results showed that there is a direct relationship between the scour hole depth and the Froude number and that the scour hole depth increases with the increasing Froude number. Conclusion: In this study, the effect of air injection system on the scour pattern and sedimentation around the bridge pier under clear-water conditions in a straight flume was experimentally investigated. All experiments were done with four Froude numbers of 0. 18, 0. 2, 0. 22, and 0. 24 and 7 different numbers and installation levels of the aeration pipe at the air injection rate of 100 lit/min. The results showed that aeration structure in the flume reduced the scour depth around the pier. The reduction of the scour depth at the front part of the pier in the single-pipe test was 25. 5% with an installation level of 5 cm, Froude number of 0. 18, and air injection rate of 100 lit/min. The results of comparisons aiming to investigate the effect of the number of aeration pipes on the pier showed that the three-pipe mode had the lowest efficiency. This system reduced the volume of scour hole around the pier. Therefore, it can be concluded that the application of this structure can be an appropriate alternative in comparison to the commonly used protective structures; therefore, further research is suggested with this respect.

One way to decreases the damage caused by cavitation in spillways is aeration flow using aerators. The required air flow of aerator is one of the most important factors in their design. In this study, to estimate the required air flow of spillway aerators four methods were applied including of stepwise regression, Pfister empirical method, neural network (based on Levenberg- Marquardt algorithm) and the combination of fuzzy-neural (ANFIS). In order to perform of modeling, 914 experimental data on physical model of Clyde Dam spillway and 12 data of Azad Dam related to conducted tests by Water Research Center on Azad dam hydraulic model were gathered. However, the performance and error of these methods were investigated after calculating the required air flow of aerators. The results showed that the combination of fuzzy-neural has the best performance with a root mean square error (RMSE) and correlation coefficient (R) about 0.0194 and 0.968, respectively. In addition, artificial neural network, stepwise regression and Pfister empirical methods had a root mean square error equal to 0.0538, 0.0596 and 1.98, respectively.