Research On The Inner Flow And Thrust Characteristics Of Water-jet Propulsion

With the widespread use of water jet propellers on ships,people are increasingly demanding their performance.As the core power component of water jet propeller,the impeller is easy to cause cavitation when it runs underwater.The generation of cavitation will cause the thrust to drop.The cavitation will cause the corresponding propulsion efficiency to decrease,the unit vibration to increase,and the noise to increase.This poses a threat to the safe and stable operation of the waterborne vehicle.This paper is based on the National Natural Science Foundation(No.51879120),The internal flow characteristics,such as start-up transition process,cavitation,modal analysis,and thrust characteristics of water jet propeller,are analyzed by three-dimensional numerical calculation method.(1)The domestic and international waterjet propeller cavitation,thrust,pressure fluctuation,pump impeller blade inlet side form,pump start transition process,pump impeller vibration characteristics,are summarized.The waterjet propeller was modeled in three dimensions using Creo software.The ICEM-CFD software is used to perform preliminary calculations on numerical calculations such as meshing,grid-independent inspection,boundary condition setting,and selection of appropriate cavitation models.(2)Unsteady numerical simulation of water-jet propeller under design conditions is carried out to analyze the transient flow characteristics and blade mechanical characteristics of impeller during start-up transition process.The variation of the external characteristics of water jet propeller with time during the start-up transition process is obtained.The distribution of pressure and liquid phase during the whole process of impeller from stationary to rotational speed stability is studied.With the increase of the impeller speed,the low pressure zone becomes larger and the cavitation increases.When the speed reaches the maximum and stable,the pressure difference between the suction surface and the pressure surface of the blade is the largest,and the cavitation is the most serious.The analysis of the mechanical characteristics of the blade ensures the safe operation of the impeller under this complex flow,and verifies the rationality of the model design.(3)Cut the inlet side of the impeller of the water jet propeller,obtaining different cascade density,and perform the numerical simulation of the corresponding water jet propulsion pump.The cavitation performances of water jet propulsion pumps with different impeller blade inlet edges were investigated and compared under different cavitation numbers.For different waterjet pump models,monitoring points are set at the impeller inlet,at the tip clearance,between the impeller and the vane,and the non-fixed constant value is simulated and the pressure fluctuations under different cavitation numbers are analyzed.Comparing the steady and unsteady calculations,it is concluded that the cavitation performance of the water jet propulsion pump corresponding to the second cutting of the impeller blade inlet side is optimal.(4)Thrust test of water-jet propeller at different rotational speeds shows that the thrust test values are slightly higher than the theoretical values in the design.Numerical simulations are carried out on different waterjet propulsion models and their pumping devices.Under the uncut state,the thrust magnitude and trend at different speeds were basically consistent with the experimental values.At different speed of rated speed and rated speed,the thrust of the waterjet propeller increases after cutting,and the thrust of the second cutting is the largest.The thrust of the rotating and stationary parts corresponding to the second cutting takes the largest proportion of the static thrust under different cavitation numbers and different flow rates of water jet propulsion pumps.(5)ANSYS ACT is introduced to analyze the underwater prestressing modal of blade of water jet propeller.The natural frequencies of the blades were compared for different media,different impeller blades,different rotational speeds,with and without pre-stress,with and without cavitation.The external impeller is simplified into a cylindrical water space.The response surface method is used to analyze the influence weight of the parameters of the cylindrical water body on the natural frequency of the blade.It is concluded that the flow of the water jet propeller and the impeller clearance have a great influence on the natural frequency of the blade.