Ali Forudi Khowr; Mahdi Azhdary Moghadam; Mojtaba Saneie
Abstract
This study aimed to analyse the design of spillway in curved plan and downward angle of convergence. In this plan the effective length of the spillway is reduced from the crest to the toe for several times. Tests were carried out in two stages. In the first stage, a physical model of the real sample ...
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This study aimed to analyse the design of spillway in curved plan and downward angle of convergence. In this plan the effective length of the spillway is reduced from the crest to the toe for several times. Tests were carried out in two stages. In the first stage, a physical model of the real sample was prepared for a specific site in the scale of 1:50. In this stage, experiments were performed for eight different discharges making up to 25 to 150% of the design discharge of the real sample. The spillway demonstrated a satisfactory performance up to the discharge of 1.13Qd (Design Discharge). Gradually an increase in the discharge led to a decrease in the performance of the spillway so that with a discharge of 1.26 Qd the spillway was fully submerged and the downstream channel took control of the discharge. Observations and experiments indicated that one of the factors contributing to the swamp of the spillway was a severe variant of the guide wall (120 degrees) as well as the considerable decrease in the ratio of channel length (Lch) to crest length (L), i.e. . In the second stage, the effect of variation of convergence angle of the guide walls of the spillway was studied. To this end, a physical model with three convergence angle of the guide walls, including a 0-degree angle and ratio of ; a 60-degree angle with ratio of ; and a 90-degree angle with ratio of was tested. The effect of variations of angles in discharge coefficient was reported to be negligible before the swap. At the 0-degree angle with ratio of , the highest discharge was 1.99 because the model was not submerged in a discharge equal to the PMF discharge of the real sample. In all angles, the static pressure on the crest was reduced while it was increased in the shoot and toe. So that, in the crest a ratio of was recorded for a discharge of 1.13 Qd. At the angles of 90 and 120 degree, higher discharges led to swamp of the spillway and a change of the current flowing on the spillway from supercritical to subcritical. The high pressure was reported to be of the 120-degree angle for a discharge of 1.5Qd. Since at the 60-degree angle ( ), the length of the crest was smaller (45% less than the 120-degree angle with ), it was selected as the proper angle.
Mojtaba Saneie; Mahdi Azhdarimoghadam; Amin Hajiahmadi
Abstract
One of the sediment controlling methods in the hydraulics structures is application of the vortex settling basin. Such basins represent the higher speed in sediment separation in comparison with other usual settling structures. One of the problems of such settling structure is the settlement of a portion ...
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One of the sediment controlling methods in the hydraulics structures is application of the vortex settling basin. Such basins represent the higher speed in sediment separation in comparison with other usual settling structures. One of the problems of such settling structure is the settlement of a portion of the sediments on the basin floor as a result of disruption on the structure operation caused by remaining loads. Therefore, the curvature submerged vane was introduced by this research in order to solve the problem. Several curvature vanes patterns was applied in an experimental model of the vortex settling basin to investigate the efficiency and sediment removal from the basin floor. Experiments were carried out in a basin with diameter of 96 cm and a height of 206 cm. In this model, curvature submerge vanes were used for modification and their different arrangement in 60 degree diameter section for increasing in vortexes power. Experiments were continued by 45 and 37 Ls-1 water discharge, flushing orifice diameters of 36, 46 and 59 mm and six different arrangement of vane (R2, R3, R4, R23, R34, R234). Results showed that application of submerged vane on the vortex basin floor with suitable arrangement resulted in sediment removal from basin floor and in replacement of sediments toward the orifice. Present research showed that the best efficiency was obtained from R3, R4 and R34 arrangements which were located in the farther distance from orifice. Furthermore, results showed that variation in water discharge and orifice diameter is an effective factor in the efficiency of curvature submerged vane. In the most optimum case of curvature submerged vane arrangement, 25.56 percent of the sediment was removed from the floor of vortex settling basin.
