نوع مقاله : مقاله کامل علمی پژوهشی
1 دانشگاه شهید چمران- دانشکده مهندسی آب
2 گروه سازه های آبی، دانشکده مهندسی علوم آب، دانشگاه شهید چمران اهواز، اهواز، ایران
عنوان مقاله [English]
Background and objectives:
Downstream of slope control structures in watershed engineering, it is necessary to create a hydraulic jump to dissipate excess energy to prevent the destruction of the structure. Stilling basins of the hydraulic jump type with a rough bed to increase the amount of energy loss and reduce the length of the hydraulic jump can lead to economic savings in watershed affairs. In this research, a new type of roughness, which is similar to the appearance of the ripple bed in alluvial rivers, was used to reduce the length of the hydraulic jump and increase the energy loss.
Material and Methods:
The experiments of this research were carried out in a rectangular flume with width, height and length of 0.3, 0.4 and 12 meters respectively. Five different arrangements of the bed form along with the control bed form were made in five different Froud numbers from 3.5 to 5.5. An Ogee weir with a height of 32 cm was installed 3 meters downstream of the flume inlet to create a hydraulic jump, and the minimum flow depth on the crest of the weir was set to be more than 3 cm to avoid the effect of surface tension. During the experiment, the water level profiles at the hydraulic jump site were measured by a depth gauge with an accuracy of ±1 mm. During the experiment, digital photos were also taken and the required data was extracted by digitizing these photos. The average flow depth measured and extracted from the photos was used in the analysis to reduce the error. Rolling length, jump length and water surface profile were measured in each experiment and repeated three times. These lengths were also extracted from the photos and the average values were used in the analysis.
Results and conclusion:
The results of the investigation of the change of the ratio of conjugate depths showed that by changing the layout of the bed form from type 1 to type 4 of the current research, the ratio of conjugate depths of hydraulic jump decreases. This change is such that in the type 4 bed form compared to the control bed form, a maximum decrease of 10.2% was observed. The study of the change in relative energy loss also showed that by changing the layout of the bed form, similar to the above process, the relative energy loss increases, and in the type 4 bed form, compared to the control bed form, a maximum of 23% increase in energy loss was observed. In the investigation of the relative length of the hydraulic jump and also the relative length of eddying, it was observed that by changing the bed form from type 1 to type 4 of this research, the relative length of hydraulic jump and the relative length of rolling decreased and in the type 4 bed form, it was 32 and 34 respectively. percentage, compared to the smooth bed, decreased.