The Improved Research Of Waterjet Pump Blades Based On Three-dimensional Inverse Design Method

As a special kind of ship propulsion,waterjet propulsion has been used more and more widely from civilian boats to naval vessels and scientific research devices and obtains more and more recognition for better maneuverability,durability and seaworthiness.Therefore,developing waterjet propulsion equipment with reliable performance has become a hot topic for waterjet manufacturing enterprises.This paper is based on the research background of enterprise project of “new products of waterjet propulsion power assembly for a boat”.According to the requirement,the power assembly matching of a waterjet pump connecting with a diesel engine which rated power is 96 kW and rated speed is 3600r/min is needed to be verified.The efficiency of waterjet pump is very low during the actual operation and the the matching of power assembly must be adjusted on the basis of the result of verification.On the premise of using 96 kW diesel engine,blades of impeller and guide vane are optimized by three-dimensional inverse design method to improve the performance of waterjet pump and achieve a reasonable matching of the power assembly.At the same time,providing method support and theoretical reference for the new production development.In view of above research purposes,the main contents of this paper are as follows:1.The verification of effectiveness of numerical simulation is carried out under several flow conditions with the speed of 2900r/min while numerical results are compared with experimental data of original pump.Then according to the similarity theory,converting the experimental results to these data under speed 3600r/min and the power assembly matching is verified.After putting forward the improvement target of the waterjet pump on the condition of rated speed 3600r/min and rated power 96 kW through the pump theory,the original pump is simulated to verify power assembly matching under the target condition and the performance and flow field are analyzed to provide reference for further study.2.Combining inverse design method with a large number of numerical simulations to research the influence of inverse design controls parameters such as the meridional plane,the blade loading distribution of impeller,the blade stacking,the impeller blade thickness distribution,the blade loading distribution of guide vane and the trimmed guide vane lines on the geometry,performance and flow filed and which influence rules are summarized.3.According to the rules discovered from previous research,carrying out the final optimal design and predicting the performance of improved pump by simulation.The following conclusions are obtained from the above work.1.The effectiveness of the numerical simulation method is verified which lays the foundation for further research.At the rotation speed of 3600r/min,the efficiency of waterjet pump is low and sometimes actual power required is greater than 96 kW and which means that there are some issues on the power assembly.In order to meet the requirement of new power assembly,the improved target is calculated that the rated speed is 3600r/min,the rated mass flow is 300kg/s,the design head is 26 m and the rated power is 96 kW.The simulation results of the original pump under the target condition show that the pump efficiency is 70.2%,the required shaft power is 113 kW which is more than the maximum output power of diesel engine,the range of the low pressure in channel is wide and there are bad flow states such as flow separation,secondary flows and vortex.2.The influence rules of inverse design method controls parameters show that the meridional plane affects the geometry of blade and the shape of the pump and the flow field inside of the channel significantly.The front-loading on the hub is beneficial to improve the efficiency of impeller.The after-loading on the hub is beneficial to suppress the cavitation on the suction surface.The after-loading on the shroud is not conducive to the suppression of cavitation,but the working range of the waterjet pump is expanded to the large flow direction.The positive stacking is helpful for the efficiency of pump,but the stacking causes the blade distortion to aggravate.NACA blade thickness distribution is conducive to improve the efficiency and improve the pressure distribution on the blade surface.The front-loading on the hub while the after-loading on the shroud is beneficial to obtain highest guide vane efficiency and to improve flow field.The trimmed lines of guide vane improve the pressure distribution at the outlet and could be good for the anti cavitation ability.3.On the design flow condition,the efficiency of the improved waterjet pump is 81.98%,the impeller efficiency is 91.02%,the maximum efficiency near the design flow is 83.04%,the head is 26.4m and the shaft power is 94.3kW.The flow is uniform in flow field,the performance meets the design requirements and the power assembly.On the non-design conditions,when the flow is small the pump is not suitable for a long time working because of the bad performance.The flow state is better When the flow is large,but the performance of waterjet pump declines faster with the increase of the mass flow.