Research On Bidirectional Hydraulic Characteristics Of Shaft Cross-flow Pumps With Different Airfoil Impellers

The shaft cross-flow pump device is a new type of ultra-low head pump station structure between the bulb cross-flow pump device and the axial extension cross-flow pump device[10],and in recent years,the two-way vertical cross-flow pumping station has been widely used in water transfer projects and water conservancy,which are combined with drainage and irrigation.Bidirectional vertical shaft cross-flow pump device is generally composed of a shaft flow channel,an impeller,a guide vane,and a straight pipe flow channel,it usually adopts the form of vertical shafts and uses S airfoil type impellers to achieve bidirectional pumping in pumping stations.Numerical simulation and model tests show that its forward operating efficiency is lower than that of ordinary unidirectional axial flow pumps by 5%?70%,and its reverse operating efficiency is 58%?60%.With the improvement of national energy saving and emission reduction requirements,in order to further improve the bidirectional efficiency of the pumping station,the bidirectional pumping function of the pumping station is realized by using a one-way airfoil impeller(blades rotate 180 degrees under reverse condition)for the front and rear of the shaft carrying out research,it has certain theoretical significance and engineering value for the application and development of bidirectional pumping stations.In this paper,the CFD technology is used to perform forward and reverse numerical simulation on the bidirectional vertical shaft tubular pump device of a pumping station using the S airfoil impeller and the unidirectional airfoil impeller in the form of the front of the shaft and the rear of the shaft,the precision hydraulic machine test bench carried out a two-way model test of the two airfoils impeller when the shaft was in front of the shaft,and verified the accuracy and credibility of the numerical simulation.Research findings when the front shaft of the shaft runs forward,the efficiency of the high efficiency point of the S airfoil impeller shaft cross-flow pump device is about 7%lower than that of the one-way airfoil shaft vertical cross-flow pump device.When the shaft runs forward,the impeller inlet pre-spin will affect the hydraulic performance and internal flow characteristics of the impeller are lower than the head efficiency when compared with forward operation,the flow characteristics in the impeller chamber are biased and radially moved by the pre-spin,under the design conditions,the unidirectional airfoil impeller the efficiency of the pump device running 180 degrees in reverse is about 3%higher than that of the S airfoil impeller pump device.When the shaft is placed in the forward direction,it is not much different from the shaft front,the operating conditions of the pump device operated by the same airfoil impeller remain unchanged,and the efficiency change does not exceed 1%.When the shaft is installed in the reverse direction,the hydraulic performance of the S airfoil impeller and the unidirectional airfoil impeller blades rotating 180 degrees in reverse operation is quite different,the high-efficiency point efficiency of the S airfoil impeller pump device is 60.54%,the efficiency of the unidirectional airfoil impeller pump device is 68.13%,the efficiency of the pump device in the reverse operation of the unidirectional airfoil impeller is increased by nearly 7%compared with the S airfoil impeller,the reverse operation efficiency of the pump device has been significantly improved.In reverse operation,the inlet water inlet condition of the S airfoil impeller chamber is more affected by the pre-rotation,the efficiency of the S airfoil impeller is lower than that of the unidirectional airfoil by about 3%.The flow separation phenomenon of the suction surface of the S airfoil blade is serious,the large area of the low pressure area is more prone to cavitation,and the radial movement at the hub is obvious;the unidirectional airfoil blade rotates 180 degrees and reverses the direction of the blade pressure surface,at the outlet of the suction surface of the blade,there is a radial movement from the hub to the rim,the static pressure distribution of the unidirectional airfoil blade at different heights of the blade is more uniform,and the suction pressure of the S airfoil blade near the hub is obvious.Through the comparison and analysis of the front and rear of the shaft when the unidirectional airfoil impeller blades rotate 180 degrees in reverse direction,it can be found that the efficiency of the front and rear of the shaft is 61.57%and 68.13%respectively,the hydraulic performance is obviously better than the front shaft.By comparing the hydraulic performance of the impeller,it can be found that the impeller head and efficiency of the shaft at the rear of the shaft are larger than the front of the shaft,and the inlet water inlet condition of the impeller chamber is better when the shaft is located at the rear,better water inlet conditions make the impeller have higher head and efficiency.