Study On Flow Characteristics And Optimization Design Of Water-jet Propulsion Reversing Bucket

The marine water-jet propulsion has the advantages of strong anti-cavitation ability,good maneuverability,low noise,small resistance and vibration.It is widely used in high-speed passenger ferries and military high-performance ships.At present,the research on water-jet propulsion has gradually matured at home and abroad,but the research on the water-jet propulsion reversing bucket is rare.The traditional reversing bucket has poor hydraulic performance and low reversing efficiency,which seriously threatens the safety of the ship's navigation.Therefore,this paper studies the flow characteristics of the internal flow field of the reversing bucket,and optimizes the structural parameters of the water-jet propulsion reversing bucket to improve the hydraulic performance.The main achievements of this paper are as follows:(1)Three-dimensional modeling of the water-jet propulsion reversing bucket was carried out.The structural grids were divided for each calculation domain and the grid independence was verified.Using CFD software to calculate the steady value of the water-jet propulsion reversing bucket at different inlet velocity.The thrust performance curve obtained by the steady flow calculation of the reversing bucket model agrees well with the experimental data,which verifies the accuracy of the numerical simulation.The flow characteristics in the reversing bucket are analyzed.The results show that due to the centrifugal force,the pressure gradient and energy loss in the passage turn are large and the flow is disordered.Due to the interaction between mainstream and environmental flows makes the velocity field and pressure field distribution in the flow passage very uneven.(2)Using the method of control variables,the numerical simulation of the reversing bucket model under different structural parameters is carried out.The effects of different structural parameters on the internal flow field and thrust performance of the reversing bucket are compared and analyzed.The results show that the placement angle of the deflector is too large or too small,which is not conducive to the distribution of the flow field in the flow passage.The thrustgradually increases with the base point placement distance and the thickness of the deflector decreasing.(3)To investigate the gas-liquid two-phase flow characteristics in the reversing bucket of water jet propulsion,the numerical simulations based on the Euler-Euler inhomogeneous model was conducted to the internal flow field of the reversing bucket.The calculation results show that the gas mainly distributes in the inner part of the reversing bucket flow passage under different inlet gas volume fractions.At the higher gas concentration in each cross-section,where the vortex will exist,indicating that the gas concentration has a great relationship with the vortex aggregation.The appropriate gas can effectively improve the thrust efficiency of the reversing bucket.(4)Based on the original design model of the reversing bucket deflector,the multi-objective optimization design of the water-jet propulsion reversing bucket is carried out by using Box-Behnken Design experimental design and response surface methodology.Verifying the significance of the optimization model,it is feasible to optimize the design of the reversing bucket by applying the response surface methodology.The results show that thrust is increased by about 2.5%,the pressure gradient and flow field in the passage are significantly improved.The maximum pressure of the bucket wall is reduced from 133465 Pa to 127468 Pa,which is reduced by about 4.5% compared with the original model.The hydraulic performance of the reversing bucket is effectively improved.