بررسی آزمایشگاهی تأثیر زاویه و موقعیت صفحه های نفوذناپذیر مستغرق بر جریان غلیظ

Nowadays, the construction of dams is one of the most important solutions for the storage of surface water. Due to fresh water limitations, the construction of reservoir dams to control the surface water resources in Iran is inevitable and necessary. In dam reservoirs, the turbidity current is usually the cause of sediment transfer and deposition. If the current is completely stopped in the middle areas of the reservoir, the amount of sedimentation will be reduced at the bottom of the dam wall and, as a result, the main functions of the dam will not be disturbed. Therefore, it is necessary to study this phenomenon. One of the methods for hydraulically changing the turbidity current is to roughen it or to use a barrier in the bed. Several studies have been carried out on the turbidity current velocity so far, and controlling it by roughening and barriers. However, it seems that no studies have been made on the effects of the angle and location of submerged impermeable plates on the turbidity currents.
In this study, 42 experiments were carried out on the effects of the submerged impermeable plates on the head velocity and the height of the turbidity current head. For this purpose, an experimental flume with 30 cm width, 10 m length and 46 cm height was used. The turbidity current entered the flume with concentrations of 20 and 40 g/l, and bed slopes of 1 and 2%. In order to investigate the effects of the angle of the submerged impermeable plates, impermeable plates which came into seven different mounting angles of the plates with respect to the current axis (0, 15, 30, 45, 60, 75, 90 degrees) and also, impermeable plates with eight locations were located across the current. Measurements of velocity and height of the head turbidity current were made on six sections with 50 cm distances. Then, based on the data obtained, and by dimensional analysis of Edgar Buckingham’s method (Buckingham π methodology), the non-dimensional graphs of velocity, height and Densimetric Froude Number of the head of turbidity current were plotted.
According to the performed experiments, the results of this study are presented in two sections. In the first section, the results are related to the effect of the plate angles; in the second, the results are related to the effect of the plate positioning. Generally, due to the collision of the turbidity current with the plates, the non-dimensional velocity was reduced along the mounting route. Also, the Densimetric Froude Number was decreasing along the current route. The results showed that by increasing the plates’ angle, the decreasing gradient of the dimensionless velocity increases along the dimensionless route. Therefore, the plates with angles of 75° and 90° which are in the vertical and near-vertical position relative to the current axis, are affecting the current velocity more than plates at other angles. In general, the turbidity current velocity decreased by 8.6 to 27.1% with respect to the control state, in case of different angle of mounting of the plates with respect to the current axis. With a concentration of 20 g/l and the slope of 1%, the plates with the mounting angles of 75 and 90° relative to the horizontal axis of the turbidity current provide the most significant decrease in the velocity in comparison with the control, with 26.4 and 27.1%. The analysis of the plates’ position showed that when the plates are mounted across the canal’s total width, they provide the most significant reduction in the velocity in comparison with the control. In general, in different conditions, the turbidity current velocity increases to 6.3% in the worst location and decreases to 45.1% in the best location relative to the control state (in bed without submerged impermeable plates). With a concentration of 20 g/l, the plates at the position of 2, with 45.1% at the slope of 1%, and 29.5% at the slope of 2%, made the biggest decrease in the current’s head velocity in comparison with the control. Also, with the concentration of 20 g/l at the slopes of 1 and 2%, the position 5 made the biggest decrease in the velocity with 33.9 and 38.3%. Slope investigations showed that with the concentration of 20 and 40 g/l, the slope increase will reduce the effect of the plates on the velocity.