Research On The Inner Flow Of Water-jet Propulsion

Marine engineering equipment and high technology ships has become a key research project along with the “Made in China 2025”.Water-jet has been widely used in novel propelling device because of its advantage of high efficiency,good suction performance,low vibration noise and high critical navigational speed.Only the change of ship speed and rotating speed affects the internal flow in the running of the water-jet propulsion without considering the reversing gear and steering gear.It is of great significance for the shock absorption and noise reduction of water-jet propulsion by analysis the internal flow of water-jet propulsion at different ship speed and rotating speed.It's important not only show the flow regime at different conditions,therefore,but analysis the pressure fluctuation and cavitation of water-jet propulsion.The pressure fluctuation and cavitation in contra-rotating axial flow water-jet propulsion were revealed by using steady and unsteady numerical simulation under different conditions.The main work and innovations were:(1)Methodic summarized the research status about the internal flow of waterjet propulsion from internal and abroad.Cavitation and pressure fluctuation of rotating machinery were summarized in this paper.The three-dimension model was made by the software Creo and the mesh generation was conducted by the software ICEM-CFD by using hexahedral structured grid and unstructured grid.Some accurate numerical models include SST turbulence model and Zwart cavitation model are chosen and corrected?(2)The performance analysis of the counter-rotating axial flow pump and waterjet propulsion were taken to verify the accuracy of the numerical calculation.The full flow passage numerical simulation of the water-jet propulsion was performed at different vehicle speed and rotating speed.Velocity and pressure characteristics at different cross-sections were carefully observed.Simulation results indicate that that flow field in water-jet propulsion particularly in suction pipe and front impeller is greatly affected by vehicle speed.Velocity and pressure change obviously at different speed.With the increase of speed,the flow rate of the water jet propeller increases and flow turns more complex.Flow separation occurs in suction duct and a vortex is observed at upper half.The increase of rotating speed stabilized the internal flow of water-jet propulsion.The flow state is basically the same after the rear impeller under different ship sheep and rotating speed.(3)Monitoring points are mounted at the inlet of front impeller,in the tip region of front and rear impellers,in the axial clearances and at the diffuser inlet.The time domain pressure fluctuation data are recorded at each monitoring point,meanwhile the pressure fluctuation characteristics are analyzed and compared in both time and frequency domains.Simulation results indicate that pressure fluctuation is mainly affected by blade passing frequency.The rotor-stator interaction between guide vine and rear impeller can also lead to the change of pressure fluctuation.Pressure fluctuation at tip clearance of front and rear impeller affected by two stage impeller and guide vine.The monitoring point position is different,which flow components have the biggest influence is depending on the location.Pressure fluctuation between front and rear impeller is the biggest in axial,because of the opposite rotating between front and rear impeller and complex flow field with greater pressure fluctuation.(4)Based on the numerical simulation method,the cavitation flow in water-jet propulsion were revealed under different conditions.The results shows that cavitation appears at the front impeller under high rotating speed.Cavitation become more apparent with the increase of rotating speed.Cavitation at lower part of impeller passage is worse than upper part because of the mass transfer,the cavitation shedding appears at the inlet of guide vine and tip clearance.The rear impeller have good performance in cavitation because of the structure of contra-rotating.