Design Method And Experimental Investigation Of New-type Deep-well Centrifugal Pumps

Deep-well centrifugal pumps, the main equipment for pumping groundwater, have been widely used in field irrigation, geothermal resource utilization, oil exploration and other fields. Recently, the groundwater levels are declining, geothermal and other new energy technology are getting increasingly popular, the users of deep-well centrifugal pump have growing demand, and the requirements for pump performance are also increasing. In this paper, based on theoretical analysis, experimental measurements and numerical simulation, the detailed design method of new type multi-stage deep-well centrifugal pump has been systematically studied. The main research contents and creative achievements are as follows:1. The steady numerical simulation methods of deep-well centrifugal pump were analyzed, the influence of stages number, turbulence models, grid number and other key parameters were compared respectively. Based on the analysis of pump head, efficiency and axial force, a suitable simulation method for multi-stage deep-well centrifugal pump was established. Two stages pump models could be used to predict the external characteristics of the entire pump, which is not only have less computational grid and computational time, but also have enough high simulation accuracy.2. Uncertainty analysis of the pump performance test rig used in this paper was carried out. The random uncertainty of pump head, flow rate, power and other key parameters were determined based on ten times measurements. According to the systematic uncertainty caused by the measuring instrument inherent error, the overall uncertainty of pump efficiency was calculated. The results prove the overall efficiency uncertainty is 0.73%, which meets the accuracy requirements of national 1-level and international A-level.3. The design method of oblique centrifugal pump used in the new type deep-well centrifugal pump has been introduced. Based on numerical simulation and experimental measurement, the influence of impeller inlet edge position and impeller front shroud position on pump performance was investigated. Appropriate extension of the impeller inlet edge position can be improved impeller outlet flow field distribution. The forward move of the impeller front shroud leads to the increasing of the impeller outlet width, correspondingly the single-stage pump head and shaft power is gradually increased, the pump best efficiency point (BEP) offset to a large flow rate, and the value of maximum efficiency is also showing a decreasing trenc’.4. The influence of impeller rear shroud diameter on axial force and pump efficiency has been studied. Five impellers’rear shroud radius were determined by the Golden Section method, and then assembled with the same diffuser to carry out the test and simulations. According to the test results, oblique trimming of the impeller rear shroud radius could lower the axial force effectively, but the undersize rear shroud radius also causes the sharply decline of pump performance. Along with the decrease of the rear shroud radius, the best efficiency point is drifting to the smaller flow rate.5. Based on the theoretical analysis and numerical simulation, flow field distribution at oblique impeller outlet was analyzed, the results show that the axial velocity moment showed a gradual downward trend along the impeller outlet edge. According to such flow characteristics, a new type three-dimensional surface return diffuser (3DRD) was designed. The hydraulic performance comparison of 3DRD and cylindrical surface return diffuser confirmed that 3DRD have smaller hydraulic losses, since its variable diffuser inlet setting angle is more consistent with the flow pattern. Meanwhile, the concept of the diffuser efficiency was defined to quantify the diffuser pressure conversion capabilities, and the difference of diffuser efficiency between stages also was compared.6. A special test rig was designed to investigate the flow filed using Particle Image Velocimetry (PIV) measurements. The flow field difference under 1425r/min and 2850r/min was compared. The results show that the external characteristics under two rotating speed are following the similar conversion laws, and the flow patterns inside the diffuser flow channel are similar. At the rated flow, the internal flow patterns are stable and regular. But the large scale flow separation and back flow appear under the part-loading flow conditions, and the swirl intensity gradually strengthened as the flow rate decreasing.7. The unsteady numerical simulations were conducted with sliding mesh technology and three different turbulence models, which includes SST k-co model, Low Reynolds SST k-ω model and DES model. Based on the structured mesh, the grid independent analysis was carried out, and the influence of mesh number on microscopic parameters of the flow field was compared. A detailed calculation of the numerical uncertainty due to discretization was presented. At rated flow and larger flow rate, the velocity fields predicted by three turbulent models have a good agreement with PIV measurement results, and the streamlines patterns are basically similar. The numerical simulation error is getting larger under the part-loading flow conditions. Overall, velocity distributions predicted by Low Reynolds SST k-co model are closer with PIV results, especially it has the higher prediction accuracy on vortex shape and vortex core position under the part-loading flow conditions.8. Series of new-type deep-well centrifugal pumps were developed, which have high single-stage head, short axial length, light weight, high efficiency, energy saving and material saving features, and widely application prospects.