| Multistage centrifugal pumps are widely used and play an important role in various fields,but most of the industrial centrifugal pumps have low performance,and the problems of reduced hydraulic characteristics and shortened life expectancy caused by cavitation have become the research direction of many scholars.In this paper,a multistage centrifugal pump is taken as an example,and the state of cavitation occurring at the minimum pressure of the impeller at the head stage is called initial cavitation,and the corresponding cavitation allowance is called primary cavitation allowance by means of numerical calculation.In engineering,when the lift was 3%lower,its working state is called the critical cavitation,and at the same time of the device for critical cavitation cavitation allowance allowance,and USES the control variable method,the key hydraulic components to the improved design,through the analysis of different impeller inlet and the water absorption chamber of liquid medium flow state,the multistage pump hydraulic performance and cavitation performance were studied,It is of great engineering significance and academic value to obtain an optimal impeller structure and suction chamber structure for improving the cavitation performance of multistage centrifugal pump.The main research results of this paper are as follows:(1)Cavitation allowance analysis of multistage centrifugal pumps under different working conditionsUsing the method of numerical simulation,the relationship between hydraulic performance and flow rate of multistage centrifugal pump in steady state is obtained by numerical calculation.Compared with the experimental results,the efficiency of multistage centrifugal pump increases first and then decreases with the increase of flow rate,and reaches the maximum at rated condition.The criteria and basis of primary and critical cavitation of multistage centrifugal pump are proposed according to the different states of cavitation.The occurrence points of primary and critical cavitation of multistage centrifugal pump are analyzed,and the distribution of cavitation volume fraction of the impeller at the head stage is observed.The primary cavitation point is taken as the cut-off point of the pump cavitation.The installation conditions of the pump are determined according to the primary cavitation allowance of the special pump,so that the multistage centrifugal pump can run stably and without cavitation under normal state,thus improving the operation life.(2)The influence of the inlet diameter of the head impeller on the performance of multistage centrifugal pumpDesign the head of three different inlet diameter size of impeller on other variables of the same circumstances,with the method of numerical simulation,get three schemes of hydraulic performance and cavitation performance,the research results show that the head through the impeller inlet diameter properly after the increase of its internal stress distribution situation has improved,on the impeller outlet and impeller inlet movement symmetry,And the range of low pressure area decreases;With the increase of impeller inlet diameter,the cavitation resistance of the three schemes also shows a rising trend.When the critical cavitation residual value decreases.the volume fraction of bubbles on the blade surface also decreases when the critical cavitation pressure is reached,so the anti-cavitation performance is improved and the improvement effect is obtained.The study shows that increasing the inlet diameter of impeller appropriately is beneficial to improve the anti-cavitation performance of the pump.(3)Influence of inlet pipe shape of suction chamber on performance of multistage centrifugal pumpDesign a kind of annular water chamber,by changing the shape of the inlet pipe before into the suction chamber,respectively designed for deflating,diffusion type,straight type three kind of schemes,by comparing the three options under the water absorption of the ministry of interior flow field distribution,from the inner flow field of fluid velocity,stability analysis for comparison,get a kind of design scheme to improve pump cavitation performance.By comparing the suction chambers of the three schemes,it is found that the suction chamber of the straight tube inlet pipe has the least influence on the cavitation performance of the multistage centrifugal pump,and the cavitation resistance is the best.Under rated working conditions,the suction chamber efficiency and head of straight tube inlet pipe are the highest,with the efficiency increased by 5.7%and 3.6%respectively,and the head increased by 3.4%and 1.6%respectively.In the annular suction chamber of straight tube inlet pipe,the vortex intensity decreases,the streamline distribution is uniform,the low pressure area of impeller inlet decreases obviously,the volume fraction of cavitation on blade surface decreases obviously,and the cavitation is inhibited.The critical cavitation allowance is 1.1m and 0.3m lower than that of the contraction type and the diffusion type,respectively,and the cavitation generated at the inlet of the first impeller of the suction chamber of the straight cylinder inlet pipe is less.This study has a certain theoretical value for the shape design of the suction chamber. |
