Analysis On Flow Characteristics And Hydraulic Characteristics Of S-type Blade Of Centrifugal Pump

Low specific speed centrifugal pump is widely used in life,engineering,chemical industry and other fields because of its small flow and high head.As one of the main components of low specific speed centrifugal pump,impeller has narrow and narrow flow channel and small outlet width,resulting in large disc friction loss and low operation efficiency.The reason is that the internal flow mechanism of the pump is unclear.There are unstable flow pheno mena in the impeller channel,such as velocity slip,blade passage vortex,flow separation,jet wake structure and reflux,which destroy the stability of the internal flow field structure,which is a barrier to the performance prediction and optimal design of low specific speed centrifugal pump.Based on this,this subject takes a certain type of low specific speed centrifugal pump as the research object.Based on the hexahedral structure grid adopted in the whole basin,RNG k-εThe effects of impeller geom etric parameters on the hydraulic performance and flow characteristics of S-blades of centrifugal pump were studied.The specific research contents are as follows:（1）Under the condition of keeping the other geometric parameters of the impeller unchanged,only the blade outlet angle is changed,the blade is modified and designed on the basis of the original blade outlet angle,the scheme of large outlet angle blade of centrifugal pump is put forward,and the impeller hydraulic model of S-type blade is constructed.Five kinds of centrifugal pumps with blade outlet angles of 50°,60°,70°,80°and 90°are numerically calculated.Through the study and analysis of the hydraulic characteristics and internal flow field structure of the pump,it is found that the head of the centrifugal pump increases with the increase of outlet angle.When the blade outlet angle is 90°,the head and efficiency of the centrifugal pump are the best.At the design working point,the head is increased by 8%and the efficiency is increased by 1.67 percentage points;The modified large outlet angle scheme reduces the efficiency under small flow conditions and improves the efficiency under design conditions and large flow conditions.When analyzing the flow characteristics of S-shaped blade with blade outlet angle of 90°,it is found that S-shaped blade can effectively inhibit the boundary layer separation inside the impeller and reduce the hydraulic loss caused by flow separation in the channel,but the loss of S-shaped blade in the channel corresponding to the diaphragm is large,and there is vortex at the blade outlet,which is one of the important factors affecting the efficiency of S-shaped blade centrifugal pump.（2）In order to further improve the flow condition in the impeller and weak en the jet wake structure at the impeller outlet,a splitter blade is placed in the middle of each two blades at the impeller outlet of the above schemes.The splitter blade takes the impeller outer diameter as the scale reference and has two lengths,0.45D₂ and0.25D₂ respectively.Through the analysis of the hydraulic characteristics and internal flow field structure of the pump,The scheme with a splitter blade with a length of0.45D₂ can obtain better hydraulic performance.By weakening the jet wake stru cture at the impeller outlet,the hydraulic loss can be reduced and the pump head can be increased;On the whole,when the outlet angle is 90°and the S-shaped blade scheme with splitter blade has the best hydraulic performance,the head is increased by 16.7%compared with the original model,but the efficiency is slightly lower than the original model pump.（3）The blade wrap angle of centrifugal pump is modified.The d esign blade wrap angles are 150°,160°and 170°respectively,and the influence of wrap angle change on the hydraulic performance of S-blade centrifugal pump is explored.The results show that the head of S-blade centrifugal pump increases but the efficiency decreases with the decrease of wrap angle.Keep the 160°wrap angle unchanged,set different blade outlet angles on the basis of it,and conduct numerical simulation for three kinds of centrifugal pumps with outlet angles of 80°,90°and 100°respectively.The results show that the hydraulic performance of s-blade centrifugal pump with wrap angle of 160°and outlet angle of 90°is the best.The head is 8%higher than that of the prototype pump,but the efficiency is reduced by 1.4%.Reducing the wrap angle and increasing the outlet angle can improve the head of the centrifugal pump,because the flow channel becomes shorter,the diffusion of the impeller flow channel of the centrifugal pump increases,and the flow loss in the impeller flow channel at the tongue of the volute of the centrifugal pump increases,resulting in the reduction of its efficiency.（4）Three S-blade centrifugal pumps with wrap angle of 160°,outlet angle of 80°,90°and 100°were added with splitter blades,and the splitter blades with length of0.45 and 0.25 times the outer diameter of the impeller were taken for numer ical simulation.The results show that the hydraulic performance of the splitter blades with two lengths is basically the same,The lift of S-type vane centrifugal pump with splitter blade is 13.8%higher than that of the prototype pump,and the efficiency is2.49%lower than that of the prototype pump.After the modification,the diffusion degree of S-blade centrifugal pump with splitter blade decreases at the impeller outlet,but vortex and reflux appear on both sides of the short splitter blade,resulting in increased flow loss and reduced efficiency.