Study On The Flow And Vibration Characteristics Of Marine Serial-parallel Centrifugal Pump

Series-parallel centrifugal pump could be used in many different places with one machine, and it has high flow-low lift and low flow-high lift two working conditions. It can work in ship auxiliary system as an important equipment, which not only reduce the occupied area but also transport working medium timely and make sure the ship’s safety. The researches about the inner flow and vibration characteristics of the series-parallel centrifugal pump have a great influence on whole ship’s space, vibration noise and environment noise. Therefore, the research of flow and vibration characteristics of the series-parallel centrifugal pump’s inner flow-field has important significance on the equipment’s replacement, optimization and vibration and noise’s reduction.Researches in this paper are developed with the help of Anhui province’s special funds for independent innovation "Oil transport and ship marine series-parallel industrialization project",51279069and51079063project of The National Science Foundation and graduate innovation fund of Jiangsu Province CXLX11₀568.So far, the researches about the inner flow and vibration characteristics of the series-parallel centrifugal pump are very rare. In this paper, on the basis of the original structure, hydraulic components were redesigned, processing technology was optimized, the vibration test-bed was built on the basis of external characteristic test-bed, and done the research by using the method of combining numerical calculation with experiment results. Main work and creative achievements are as follows:（1）In this paper, a method of hydraulic parameters was proposed on the basis of the impeller matching volute’s original structure and the design of main hydraulic parts were used this method. We also proposed a new method to fix the impeller’s front and back shround which guaranteed the channel’s surface finish and consistency of impeller’s outlet area and installing angle. What’s more, the rotor component’s dynamic balance technology was improved to enhance the dynamic balance level. On the basis of hydraulic characteristics test, a vibration test-bed was built which eliminating the vibration influence of inlet and outlet pipe and researched the vibration at the foot of turbine. After dimensionless processed the external characteristics data, got the result of how series or parallel working condition influence hydraulic performance by comparing the different working conditions. And by analyzing the monitoring points data of no-load, series rated condition and parallel rated condition, we found that total vibration level has a trend of:parallel rated condition> series rated condition> no-load.（2）We have improved the original structure （impeller matching spiral pressurized water chamber） for the first time and use a new structure of impeller matching guide vane and annular pressurized water chamber by not changing the impeller’s hydraulic designing. And tests of new type series-parallel centrifugal pump were done on the condition that rotor component’s quality, accuracy class of dynamic balance and motor are all the same. After comparing the new structure’s dimensionless data with original one’s at rated operating point, we found that new one’s efficiency is lower than the original one on both series and parallel conditions. Using total vibration level of acceleration1/3octave at the foot of the machine as evaluation index, compared the original structure with the new one, we found that the vibration difference changes at different frequency, but there is no rules to follow. Using total vibration level of foot acceleration at the monitor point as evaluation index, found that new structure’s vibration was3dB-4dB lower than that of the original one. Comparison of two structure was made by using efficiency and foot vibration as evaluation index respectively, providing a reference for selecting different optimization goals.（3） Choosing the vibration of machine foot as evaluation index, we selected the new series-parallel centrifugal pump as calculating model, summarizes the series-parallel switch in the implementation of numerical calculation method. Different turbulence models such as k-epsilon, RNG k-epsilon, SST turbulence model were applied for numerical analysis and we found the difference of head, power, efficiency, etc. among cases. By using dimensionless analysis with experimental results, we believed that the RNG turbulence model had a good adaptability in the new pump series-parallel numerical calculation, which laid a foundation for the analysis of the internal flow field. Contrast analysis of the pressure contour, the distribution of velocity, the turbulent kinetic energy as well as streamline at the cross section of the impeller, the reversing valve and the suction chamber was conducted and the influence of working conditions in series and in parallel on the internal flow characteristics was explored, which provided a foundation of the internal flow characteristics for the series-parallel centrifugal pump research. （4） Due to the influence of the structural characteristics and the preliminary selection of hydraulic design method, the primary impeller shows a deviation to large flow rate in the parallel working condition, the primary impeller’s flow rate is also greater than that of the secondary impeller in this case. While in series working condition, the flow rate of the two impellers become equal since the clearance leakage is ignored. It’s the first time in the field who proposed that the hydraulic design of series-parallel centrifugal pump should consider coupling the structure and put forward the principle of differentiated design of primary and secondary impeller.（5）The contrast analysis was conducted between original structure （impeller spiral pressure water chamber） and new structure （impeller vane match annular pressure water chamber）. The pressure pulsation of impeller outlet, reversing valve, first stage suction chamber, secondary suction chamber in each structure and the pressure pulsation of vane, annular pressure water chamber in the new structure was recorded and analyzed We found that the pulsation amplitude of impeller outlet of the original structure is significantly small than that of the new structure. We also analyzed the impeller’s radial force under the two kinds of structure forms and found that the radial force amplitude of the original structure is greater than the new one. We also explored the influence of fluid exciting force and rotor radial force on total vibration level at the machine foot.（6） Wavelet packet transform theory was used to analyze the energy changes of different structures and different operation mode in different frequency bands. The influences of different working conditions on vibration at different frequencies are drawn, providing a certain reference for the vibration reduction and noise reduction.