Study On The Hydraulic Optimization Design Method And Cavitation Of Waterjet Pump

The design of the water-jet propulsion pump is not only limited by the size of the ship's space,but also to ensure efficient and low noise operation at high speeds.For high speed ships,cavitation is the main source of noise.In the hydrodynamic design of the water-jet propulsion pump,the pump efficiency and cavitation performance are improved under the premise of ensuring the head of the pump.There is currently a lack of a cavitation prediction method that can be applied to rapidly optimize designs.Therefore,it is necessary to carry out research on hydraulic optimization design method and cavitation prediction method of water-jet propulsion pump.This paper starts with the engineering design problems in the hydraulic performance optimization of water-jet propulsion pumps,and conducts theoretical,numerical and experimental studies on the optimal design method of water-jet propulsion pump.Firstly,an efficient hydraulic optimization design strategy of the impeller is proposed to obtain the water-jet propulsion pump with superior head,efficiency and cavitation performance.On this basis,in order to establish the correlation between cavitation flow structure and cavitation performance,the evolution mechanism of cavitation flow structure in water-jet propulsion pump during the occurrence and development process is obtained through high-speed camera test.Thirdly,in order to obtain the cavitation characteristics related to cavitation performance,the numerical calculation and experimental comparison study on the cavitation flow of the water-jet propulsion pump are conducted,which provides experimental and theoretical support for the cavitation prediction method.Finally,a cavitation performance prediction method suitable for multi-parameter and multi-objective automatic optimization is proposed,and the feasibility of the prediction method is verified by experiments,so as to solve the rapid prediction problem of hydro-mechanical cavitation performance in engineering.The main contents and conclusions are as follows:?1?In order to obtain a set of high performance water-jet pump,the initial model was designed using a three-dimensional inverse design method of blade parameters.The shape of the blade was controlled by multiple parameters,and the optimized parameter sample space was constructed using a Latin hypercube.Numerical calculations were carried out to obtain the optimized target head,efficiency,and minimum pressure at the design condition.Artificial neural network was used to establish the approximate function model between the optimized target and the optimized parameters.The NSGA-II genetic algorithm was used to optimize the approximate function model.A water-jet pump impeller optimization strategy was constructed based on the coupling of multi-parameter and multi-objective genetic algorithm,which has been effectively and quickly designed a set of excellent hydraulic model.Experimental verification of hydraulic performance is carried out.?2?The cavitation vortex flow characteristics of cavitation generation and development are obtained through high-speed camera technology.The cavitation vortex structures include sheet cavitation,cloud cavitation,tip clearance cavitation,tip leakage cavitation,and perpendicular cavitating vortices.The physical process of the cavitation evolution is captured,and the impact of each cavitation flow structure on pump performance degradation are analyzed,which provids experimental references for new cavitation prediction methods.?3?In order to establish the correlation between the cavitation flow structure and the cavitation performance,and to obtain the cavitation flow characteristics that are closely related to the cavitation performance,the SST k-wturbulence model and cavitation model based on the Rayleigh-Plesset equation are adopted to conduct the cavitation numerical simulation of water-jet pump.A comparative study on the numerical calculation of cavitation and the cavitation visualization test of water-jet propulsion pump are carried out.The key cavitation flow characteristics are analyzed when the pump performance is steep.?4?Under the single-phase flow medium,the internal flow characteristics of the pump are obtained by the CFD method.The construction method of the pressure isosurface P_iso and its area ratio R_s?the pressure isosurface area divide by the blade area?is established to obtain the low-pressure isosurface area.In the design condition,when cavitation occurs,the pressure isosurface area S_iso and the NPSH_a satisfy a linear formula:S_iso=-0.014063NPSH_a+0.123204.The pressure isosurface area S_iso increases linearly with the NPSH_a.Based on this,a method for predicting the cavitation performance based on the pressure isosurface area ratio of single-phase is proposed.The prediction of cavitation performances for the water-jet pump hydraulic model under different flow rates were carried out.Combined with the test results,the research evaluates the accuracy and feasibility of the method,as well as a good sensitivity to different incoming flow.It is demonstrated that the method is suitable for multi-parameter and multi-objective automatic coupling optimization design.The cavitation performance prediction of the water-jet pump is more accurate when the area ratio is 13.718% and 13.826%.In summary,the study on optimization design method and cavitation of the water-jet pump is conducted in this paper.The blade parameterized three-dimensional inverse design method is applied to the establishment of the initial model.An optimization strategy of the water-jet propulsion pump impeller based on multi-parameter and multi-objective genetic algorithm is constructed,and a set of high performance water-jet propulsion pump is obtained.The cavitation vortex flow characteristics of the occurrence and development of cavitation are obtained through high-speed camera technology,and the correlation between cavitation flow structure and cavitation performance is established to provide more scientific cavitation characteristics for cavitation performance prediction.The method of constructing the pressure isosurface P_iso and its area ratio R_s was established,and a prediction method for the cavitation performance of the water-jet pump based on the area ratio of pressure isosurface was proposed.The method is not only suitable for cavitation performance prediction of water-jet propulsion pump,but also can be expanded to cavitation performance prediction of blade type hydraulic machinery,which will solve the problem of rapid prediction of hydraulic machinery cavitation performance in engineering.