اثرات واگرايي ناگهاني و تدريجي مقطع مستطيلي بر مشخصات جهش هيدروليكي

Effects of abrupt and gradual expansion of rectangular section on hydraulic jump characteristics

Optimum and effective operation of classical hydraulic jump in irrigation and drainage networks needs appropriate tail water in downstream of the stilling basins. For any reason whether downstream tail water of hydraulic structure is less tail water than classical jumpʹs one, establishing of expansion in flow section is an appropriate solution for decreasing necessary tail water depth, which can reduce the cost of stilling basin construction too. In this research, hydraulic jump characteristics were experimentally investigated in rectangular section with abrupt and gradual expansion. Abrupt and gradual expansions (30°, 45°, 60°, 75°, 90°) for three expansion ratios (downstream channel width to upstream) of 1.5, 2.5 ,5 were installed in the rectangular channel (in a flume with 6xl><0.7 m long, width and height respectively). For different Froud numbers of flow, hydraulic jump characteristics were measured in these sections and the results were analyzed. Asymmetric vortices (clockwise and non-clockwise) associated with jump, established in the left and right hand of the jump, as flow passed through the expanded section in which their size and rotation velocity were completely different. Hydraulic jump characteristics including secondary depth, length and depth of jump, radius and rolling velocity of the vortices were investigated. The results of this research showed that decreasing divergence angle in different expansion ratios, decreased undesirable characteristics of spatial and transitional jumps in which, finally their conditions could be better than the characteristics of classical jump. However, for any expansion ratio, modifying divergence angle from 90° to 30°, considerably affected the secondary depth (related to classical jump), but sequent depth ratio does not significantly modify. As expansion ratio and divergence angle decrease, expanded jump has shorter length related to classical jump. Hydraulic jumps in expanded section always have more efficiency than classical jump and with change of divergence angle for constant expansion ratio; this efficiency does not modify significantly. Finally, the optimum conditions of expanded jump could occur with expansion ratio of 2 and divergence angle of 60°.