Study On Energy Dissipation Of Multi-stage Orifice Spiral Flow With Varying Hole Center Distance

Long-distance pressurized water transport is one of the engineering measures to solve the uneven distribution of water resources in China.However,the layout of the pipeline is often affected by topography,and the initial pressure head is often higher than the energy consumed in the water transport process.In this case,excessive energy contained in the water flow may cause some unnecessary damage to the downstream pipeline system,and even cause safety accidents.Therefore,in order to effectively reduce the excess water head during pipeline operation and ensure the safety of downstream pipeline system,it is necessary to design a simple and efficient energy dissipation device.In this paper,a new concept of hole center distance of orifice plate is proposed based on the helical flow energy dissipation device of orifice plate.The influence of changing the hole center distance on the spiral flow energy dissipation device of orifice plate is studied emphatically.The main contents of the study include: Change the flow condition of the test pipeline,the distance between the core of the hole plate,the distance between the hole plate and the rotation Angle of the hole plate,measure the various pressure measuring sections laid by the main test pipeline,and determine the pressure difference value of each section of the energy dissipation device under different combinations of the hole plate and flow.The influence of parameters such as hole center distance of hole plate combination on the spiral energy dissipation device with variable hole center distance is analyzed and the changing rule of energy dissipation efficiency is summarized.Calculate the local loss coefficient of variable diameter section and orifice section,analyze the local head loss of each part and the head loss along the path,further determine the energy dissipation degree of each part in the test pipeline,and get the main energy dissipation area.The influence of structural parameters such as variable hole center distance on local loss of each section and along loss is summarized.By comparing with the previous hole plate spiral energy dissipation device,the advantages and disadvantages of variable hole center spacing hole plate combination and non-variable hole center spacing hole plate combination are analyzed.The main conclusions are as follows:(1)When the rotation Angle of orifice plate changes from 6 °to 18°,the energy dissipation efficiency of hole center distance of each group basically increases first and then decreases.(2)In the process of changing the orifice spacing from 3mm to 9mm,when the orifice rotation angle is 6 °,the energy dissipation efficiency of each hole center distance combination first increases and then decreases;The hole center distance combinations are 40,40,40 mm,37.5,40,42.5mm,42.5,40,37.5mm.When the rotation angle of the orifice plate is 12 °,the energy dissipation efficiency shows a decreasing trend.When the rotation angle of orifice plate is 18 °,the energy dissipation efficiency shows a decreasing trend;The hole center distance combinations are 35,40,45 mm,45,40,35 mm,30,40,50 mm,50,40,30 mm.When the hole plate rotation angle is 12 °,the energy dissipation efficiency first increases and then decreases.When the rotation angle of orifice plate is 18 °,the energy dissipation efficiency basically shows a gradually increasing trend.(3)The energy dissipation efficiency of variable hole center distance combination of 35,40,45 mm and 45,40,35 mm is better.The energy dissipation efficiency of variable hole center distance diffusion type is better than that of contraction type.(4)When the rotation angle is 6 ° and 12 °,the full range resistance coefficient with hole center distance of 37.5,40,42.5mm and 42.5,40,37.5mm has little change compared with the non variable hole center distance combination,and other hole center distance combinations have increased to a certain extent.With the increase of the variation of the hole center distance,the resistance coefficient increases,and the resistance coefficient with positive hole center distance is greater than that with negative hole center distance;When the rotation angle is 18 °,the resistance coefficient of other hole center distance combinations increases to a certain extent;Compared with the orifice plate spacing,the hole center distance and orifice plate rotation angle have a greater impact on the overall resistance coefficient.(5)The variation of the local loss coefficient of the variable diameter sudden expansion section of the water inlet under each orifice plate combination is as follows: in the same orifice plate rotation angle and orifice plate spacing,the local loss coefficient of the variable hole center distance orifice plate combination is always less than that of the constant hole center distance orifice plate combination;When the distance between the hole center and the orifice plate is constant,the local resistance coefficient decreases with the increase of the rotation angle,and the backwater degree in front of the orifice plate increases;When the hole center distance combination and the rotation angle of the orifice plate are certain,with the increase of the orifice plate spacing,the local resistance coefficient in this section mostly increases gradually,and a small part decreases gradually.In most cases,the backwater in front of the orifice plate can be improved with the increase of the orifice plate spacing.The change of local loss coefficient in the variable diameter and sudden contraction section of the outlet under the combination of hole center distance is as follows: it increases with the increase of the change of hole center distance of the orifice plate.The results show that the greater the variation of hole center distance,the stronger the spiral degree of water flow in the sudden contraction section,and the longer the spiral liquid flow can extend.(6)The percentage of the pressure difference between the perforated plate segment and the total pressure difference is 83.1%-111.1%,indicating that the perforated plate segment is the main energy dissipation area of the energy dissipation device.(7)Comparing the energy dissipation efficiency and the pressure value in front of the orifice plate of the variable hole center distance orifice plate combination,the constant hole center distance orifice plate combination and the rotating blade orifice plate combination,it is determined that the energy dissipation effect of the variable hole center distance orifice plate combination is better.At the same time,the structure of orifice plate combination with variable hole center distance is simple and easy to be applied in practical engineering.The best combination of orifice plate structure is recommended to be 13 °-15 ° diffusion angle and 12 ° rotation angle.