مهندسی عمران شریف (Aug 2020)
CIRCULAR HYDRAULIC JUMP OVER THE BEDS WITH ADVERSE SLOPE
Abstract
One of the most common energy dissipator structures is the hydraulic jump-type stilling basins, in which the flow excess kinetic energy is dissipated by the generation of a hydraulic jump, changing the flow regime from super- to sub-critical flow. Due to the extensive use of stilling basins in hydraulic systems and irrigation and drainage networks, their study was the focus of several investigations. For the hydraulic design of stilling basins, three parameters including the length, sequent depth, and head loss of the jump are the major parameters having great effects on designing economical stilling basins. In the present study, analytical and experimental investigations were performed to study the profile of circular hydraulic jumps on slopped beds with adverse slope. The study mainly focused on the conjugate depth ratio, relative head loss, and relative length. In the analytical model, we applied a series of reasonable assumptions and used integral equations governing the fluid dynamics to derive relationships for the conjugate depth ratio and the relative head loss, which are applicable to both classical and circular hydraulic jumps. Experimental study was carried out in a cubic reservoir, in which a circular bed of 2 m in diameter was applied as the circular bed in its center. In the experimental study, flow discharge, initial and secondary depth, and length of the jump were measured. According to the results, by increasing the ratio of the conjugate radius and the bed slope, the ratio of the conjugate depth and jump length decrease and the relative head loss increases. The accuracy of the analytical relationships compared to the experimental was checked, applying four error functions including; coefficient of determination, normalized root mean square, weighted quadratic deviation, and efficiency function, showing a relatively good correlation between the experimental and the analytical results. Furthermore, by using the experimental data, the length of the circular hydraulic jump was investigated. Results show that, in this type of jump, the length of the hydraulic jump is approximately half that of the classical hydraulic jump.
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