تاثیر نصب صفحات جانبی بر کنترل جریان غلیظ

یکی از عوامل کاهش ظرفیت ذخیره سازی مخزن سد و کاهش عمر مفید آن، رسوب گذاری ناشی از جریان غلیظ می باشد. تاکنون روش های متفاوتی به منظور کنترل جریان غلیظ ارائه شده است. در تحقیق حاضر، تاثیر نصب صفحات جانبی روی کنترل پیشانی جریان غلیظ به عنوان یک روش جدید به صورت مدل فیزیکی در آزمایشگاه بررسی شده است. متغیرهای مورد بررسی در این تحقیق شامل ارتفاع صفحات جانبی(3، 6 و 9 سانتی متر) و زاویه نصب آنها نسبت به دیواره(30، 60 و 90 درجه) بود، همچنین 4 آزمایش با انسداد کامل مسیر جریان برای ارتفاع های مورد نظر و یک آزمایش بدون نصب صفحات به منظور مقایسه پروفیل های غلظت بدنه جریان در حالات مختلف در نظر گرفته شد. نتایج حاصل نشان داد که برای تمام زوایای نصب، افزایش ارتفاع صفحات جانبی منجر به افزایش درصد کنترل پیشانی جریان غلیظ خواهد شد. بیشترین تاثیر صفحات جانبی در زاویه نصب 60 درجه بود که درصد کنترل به میزان تقریبا 80 درصد حاصل شد. همچنین، پروفیل غلظت بدنه جریان غلیظ در ارتفاع 9 سانتی متر و زاویه نصب 90 درجه بیشترین تغییر را نسبت به حالت بدون نصب صفحات جانبی داشت.

investigation of the effect of side plate installation on density current control

introduction the construction of dams, in spite of great profits, have consequences too; including disruption of the river’s sedimentary balance. this construction has increased the cross-section area available for flow, which causes a decrease in the flow velocity and sediment carrying capacity, which leads to sedimentation in the reservoir. in the reservoir of the dam, density current control methods can include management (non-structural) and structural methods or a combination of them, which are selected for each dam specifically and according to its existing conditions. the first and most effective measure to control the density current is to control the erosion of the watershed and trap the upstream sediments in order to prevent the production of sediments caused by erosion. an effective method that has been studied by other researchers is the method of controlling the density current using an obstacle. the study of the effect of these obstacles has been carried out in extensive numerical and laboratory researches, since the methods used in the past studies, such as creating an obstacle in the form of a rod with a high height, a plate blocking the channel in head of the flow, can increase the possibility of blocking the flow, and then the water quality of the reservoir will be affected, it is very important to use obstacles that reduce the possibility of blocking the flow, and also have easy implemention and be more stable. the purpose of this research is to investigate the effect of obstacles in the form of side plates against the density current and its control.methodology the experiments were carried out in a flume with a length of 12 meters, a height of 80 cm and a width of 40 cm. the density current used in this research was considered to be a saline flow with a concentration of 20 g/liter. the obstacles were made of glass with a thickness of 4 mm. the depth of the ambient water in the experiments was constant and equal to 50 cm. also, in all experiments, the inlet flow rate of density current and the slope of the floor were considered constant and horizontal. the height of obstacles (h) used in this research were considered to be 3, 6 and 9 cm. obstacles were installed as side plates on both sides of the flume with an installation angle (ѳ) of 30, 60 and 90 degrees to the wall in such a way that their ends were on the middle axis of the flume and the distance between the ends of the obstacles (d) on the flume axis was fixed(10 cm)(fig 2). in the conducted experiments, the velocity of the flow head and its depth concentration were measured at two depths of 4 and 6 cm, and the body concentration was measured at 7 points in the depth. after taking the samples, their salinity was read using a salinity meter and converted to concentration in grams per liter with the salinity-concentration calibration chart. concentrated, unobstructed concentrated flow test was used as a control.results and discussion based on the observations, when the density current hits the row of side obstacles, part of the flow continues its path through the obstacles and another part climbs, after descending for a while, it joins the rest of the flow and continues the path. it continues with a lower velocity and concentration, this decrease in concentration occurs with the entry of the surrounding fluid into the density current due to spreading caused by the collision of the density current with obstacles. it can also be seen that the efficiency of the complete blockage mode in controlling the density current is almost equal to the plates with an angle of 60 degrees, with the increase in height, the percentage of density current control has increased, so that at a height of 9 cm, the amount of density current control at an angle of 60 degrees is about 80 is a percentage. creating obstacles in head of the density current, in addition to the effect on the forehead, also affects the concentration profile of its body.by increasing the height of the obstacle in all working angles, the reduction of the concentration of the thick flow body is more. in such a way that at a height of 9 cm compared to the state where the flow passes without the presence of an obstacle, a large difference between the concentrations of the body in all four positions of the obstacle is observed.conclusion in this research, the effect of installing side side plates on the control of the density current head was investigated. installation of side plates is effective in controlling it due to increasing the length of headal contact with the obstacle. it should be noted that in real conditions, the density current is in the form of sediments and creating obstacles in head of the flow will lead to a decrease in velocity and as a result sedimentation. therefore, by completely blocking the flow path, the space behind the obstacle will be filled with sediment in a short period of time, and the efficiency of the installed obstacle will be lost in restraining the head of the density current. but on the side side plates, an empty space is created between the plates, due to the presence of this space, part of the flow passes through there. the results showed that the greatest effect of obstacles on the control of the thick flow head is in the case of installation angle of 60 degrees, and it is almost equal to the amount of control in the case of complete obstruction. therefore, installing side plates with an angle can be used as an alternative method. investigating the effect of installing obstacles on the shape of the concentration profile of the density current body showed that the greatest effect is related to the installation angle of 90 degrees, and with the increase in the height of the obstacle, the concentration of the thick flow body decreased more.