جستجوی مقالات مرتبط با کلیدواژه "جت ریزشی" در نشریات گروه "آب و خاک"

Grade control structures are commonly used to prevent degradation, increase bank and bed of rivers stability and prevent cross structures failure in rivers. In order to design a safe grade control structures, estimation of local scour depth downstream of these structures is crucial. In this study effect of different parameters on local scour at the downstream of grade control structures with labyrinth planform was experimentally investigated. Different types of rectangular and trapezoidal labyrinth planform weirs were studied. Experimental results showed that labyrinth planform has a high effect on reducing scour depth. It was found that decreasing the length of cycles in trapezoidal weirs decreases the depth of scour while, decreasing the width of cycles in rectangular weirs increases the depth of scour. It was found that by increasing parameter and drop height, depth of scour increases, while increasing tailwater depth decreases the depth of scour and it varied from 2 to 8 percent for labyrinth weirs. Results showed that the scour depth follows an exponential law, dimensional equation for prediction of scour depth is presented. The accuracy of developed equation was examined with the available prototype data.

Plunging pools are constructed at the downstream of dam spillways to dissipate the excess energy. The turbulent flow velocity converts to the dynamic pressure due to impact of flow with the pool’s bed. The aim of this research is to determine impact pressure of a vertical jet on plunging pool bed. Hence, the experiments were carried out in four different discharges (ranging from 6 to 27.5 lit/s according to the nozzle diameters), three jet diameters including 4.3, 5.2 and 8.2 cm and four falling heights of 37, 60, 90 and 120 cm. Also the experiments are conducted in similar flow conditions for smooth and rough surfaces, and results are compared. Dynamic pressures were measured with a pressure transducer. The analysis of data showed that increase of jet diameter causes decrement in the dynamic pressure coefficient. Results revealed an increase in dynamic pressures due to roughness of contacting surface. Moreover, variations of jet Froude number and fall length have significant effects on the dynamic pressure coefficient. The impact pressure was the highest in the surface center and was gradually reduced in outer zones.

In this article we studied the distribution limits of jet injection in the same phase and dissimilar phase ambient. To achieve the proposes of this research a physical model was set upped consist of experimental flume and related accessories, circular jets nozzles 5, 8 and 15 mm diameter which had various contraction angles. The experiments were conducted at the same phase (clear water) and dissimilar phase (air surrounding) of ambient fluid. According to the results there is a significant effect on the properties of distribution limits on the partially submerged and free jet flow. The results showed that the jet flux has been developed at the dissimilar ambient fluid in the subcritical Densimetric Froude number. While the Densimetric Froude number was supercritical range in the same phase ambient flow. The quantity investigation shows that the maximum of jet flux development in the dissimilar ambient flow in the jet nozzle diameter is about 200 times where in the same phase ambient fluid this development has the nozzle diameter occurred 400 times. The results showed that the effect of dissimilar phase ambient on development of jet flow is much greater than the same phase ambient at the concentrations of 40 to 50 grams per liter. The govern mechanisms of the flux development of free outfall and submerged jet flow and It was found that the slope of the curve of the free jet injection is more of a submerged jet.