عنوان مقاله [English]
Background and Objectives: A jump formation in stilling basins has effective roles in reduction of flow energy in downstream of hydro structures. Hydraulic jump is kind of rapidly varied flow and converts from supercritical state to subcritical state of flow in downstream by significant dissipation. In this paper, therehave been suggested a new method for decreasing both values of the conjugate depths and the hydraulic jump's length that was based on using the specifications of a rectangular free-jet for affecting to the jump features. In fact, fast impact of the jet into the jump and shifting the momentum value to it, affected the jump's specifications and situation.
Material and methods: This research was an experimental study. The experimental setup was including the flume with the walls of the glass materials in the dimensions of the 1200*30*50 cube centimeter. The depth of the flow measured by two methods of direct and indirect named. Indirect method included installing the piezometers in the flume bed and reading the height of the water column in the piezometers by a camera with a high resolution. Then it measured by a plotter of the flow’s depth software. In order to the investigation of the effect of the discharge, jet angle and bed roughness on the jump’s specifications, the tests performed in various conditions by three different jet’s discharges of 2, 2.5 and 3.2 liter per second, the jet’s angles of 60 and 90 degree versus the horizontal direction and two specific angles that their direction considered toward the maximum displacement from the beginning point of the jump direction and without any displacement and change at the beginning point of the jump direction. Also, have been used three kind of roughness.
Findings: Results have been showed, at a special jet angle, in the various dischargethe hydraulic jump had not any displacement and this angle was named as the neutral angle. As the jet’s angle increased, the jump moved toward the upstream until the angel reached to the extent with no movement of the jet to the upstream, this angle called as the maximum angle of the jump displacement. Change in the angle and discharge of the jet has beencaused changes in the secondary depth, jet length, relative energy loss and bed shear stress. Canal bed roughness was reduced hydraulic jump characteristics. Using jet withthe maximum angle, the discharge equal to the 3.2 liter per second, minimum Froude number and sinusoidal roughness, the conjugate depths ratio have been decreased of 45.9 percent. Using a jet with the angle of the 60 degrees,the discharge of the 3.2 liter per second,the maximum Froude number of the flow in the flat bed,the conjugate depths ratio had increased by 8.7 percent. The maximum reduction in the jet length (61.3 percent) occurred at the maximum jet angle, 3.2 liter per second of discharge in the minimum Froude number and the sinusoidal roughness. The maximum increasing in the jet length (15.7 percent)was happened in the angle of the 60 degrees, discharge about 3.2 liter per second with the maximum Froude numberand flat bed. Using the maximum angle of the jet, discharge about 3.2 liter per second and minimum Froude number in flat bed, shear forces were increased about 17.8 times versus without jet and flat bed. Using a jet with a 60-degree angle, was reduced shear stress to 6.6 times versus without jet and bed roughness.
Conclusion: Applying the jet to the jump with an angle greater than ineffective angle causes decreasing in the conjugate depths ratio and jump lengthand causes increasing in the energy loss and bed shear forces.