Study On Jet Vortex Characteristic And Flow Field Characteristic Decomposition Of Pump Jet Tail Under Cruise Condition

Pump-jet propulsion is a new type of propulsion method for underwater vehicle.Compared with the previous propeller propulsion method,it has the advantages of low noise,high power efficiency and good maneuverability.In this paper,the jet flow field at the tail of the pump-jet propulsion submarine model is taken as the main research object,and the influence of turbulence model on the jet flow field and vortex structure is analyzed.Characteristics of jet vortex at pump jet tail under cruise condition.DMD method is used to analyze the unsteady change characteristics of jet flow field.The main work and research achievements are as follows:1.The influence of turbulence model on the flow field and vortex structure of pump-jet jet.The whole basin simulation of pump-jet propulsion submarine model is carried out based on three commonly used turbulence models.The results show that the distribution of k-ε flow field velocity field and pressure field have obvious stratification and gradient,the flow field only has hub vortex and shear layer vortex,and there is no interaction between the two vortices.The velocity field in LES flow field distorts from the core region,resulting in fluctuations in the flow field.The pressure of flow field is lower than that of the other two models,and the stratification of pressure gradient is not obvious.The changes of vortex structure in flow field are relatively complex.Hub vortex gradually deforms from single hub vortex,and interacts with shedding vortex with the development of flow field.The velocity and pressure distribution of DES flow field are similar,and the distribution is relatively stable in the core area of jet flow.There are obvious fluctuations in the middle part of the flow field,and strong turbulence occurs in the rear section of the flow field with the development of the flow field.The vortex structure in the flow field is more abundant,hub vortices show different forms,shear layer vortices break and separate with the development of the flow field,and the influence is complicated with the generation of shedding vortices and secondary vortices.2.Vortex characteristics of pump jet tail under cruise condition.Numerical simulation of submarine model of pump jet propeller at different cruise speeds was carried out to analyze vortex characteristics in flow field.The results show that the external flow around the submarine and the external flow around the pump-jet propeller interact with the tail flow,resulting in different flow field regions.With the increase of the speed of the non-swirling zone and the increase of the flow field diffusion zone,the boat body flow around the tail jet and the strong coupling effect at a faster speed,and develop the opposite direction of the submarine.The range and energy of shear layer vortexes and the energy of shedding vortexes also increase with the speed increasing.In two rotation cycles,the vortex structure of nozzle outlet does not change with the change of speed.With the increase of speed,the decomposition of hub vortex is faster,and the distance between hub vortex and shear layer vortex is further.3.Based on DMD method,the flow field characteristics of pump jet tail are decomposed,and the flow field at different cruising speeds is decomposed by DMD method.The results show that the energy of the second,fourth and sixth order modes in the rated mode field is lower and lower,and the mode fields all produce vortices from the nozzle outlet of the initial section of the flow field and gradually increase.At low speed,the second,third and seventh order modes are vortices and flow disturbance at the nozzle nozzle at the beginning of the flow field,and the fifth mode is vortices in the whole flow field.The second and fourth order mode fields at high speed are the basic modes influenced by vortices in the whole flow field.With the increase of speed,the oscillation in the flow field is closer to the low frequency oscillation.In addition,with the higher speed,the basic mode has the higher energy,and other modes have the lower the influence on the basic mode.