| High pressure pulsed water jet is one of the basic topics in the study of hydrodynamics,which widely exists in the fields of hydropower generation,fire control and disaster reduction,farmland sprinkler irrigation and so on.But it is very difficult to improve the speed of large volume(such as 1L)liquid in technology,and the mechanical behavior of liquid accelerated by transient is very complex.Because the water jet technology driven by high pressure gas involves the compressibility of the fluid,the aerodynamic characteristics of the jet and the difference of the properties of the driving medium itself,the flow mechanism is very complex and has not been fully understood.In order to optimize the nozzle structure of high-pressure pulsed water jet,three kinds of nozzle structures are selected in this paper,which are straight nozzle,tapered gradually shrinking nozzle and tapered gradually expanding nozzle.By using computational fluid technology,the gas/liquid distribution inside and outside the tube and the hydrodynamic characteristics of the water jet are analyzed when the high pressure helium impinges on the water column to generate the pulsed water jet under these three nozzle structures.And through numerical simulation,theoretical analysis and experimental comparison,the related problems are further studied.The main results are as follows:(1)In this paper,the research object of the straight nozzle structure is based on the shock driven water jet experiment conducted by Shi Honghui,and the commercial software FLUENT is used to simulate its generation.The results show that the results obtained by the SST K-? turbulence model are in good agreement with the experimental results of pulsed water jet taken by high-speed photography(2)Based on the straight nozzle structure,in order to further optimize the hydrodynamic characteristics of the pulsed water jet,two different nozzle structures are designed in this paper:the conical gradually shrinking nozzle and the conical gradually expanding nozzle,and the simulation results of the three nozzles are compared and analyzed.The results show that the water jet with straight nozzle has larger moving distance and the water jet with tapered nozzle has larger transverse width.(3)By using 2D grid encryption technology,the calculation model of the formation process of high-pressure pulsed water jet is established,and the whole process of bubble generation in the head and tube of pulsed water jet under three nozzle structures is simulated.The pressure change of water jet and the characteristics of flow field at the head of water jet are analyzedIn this study,the numerical results of the flow field inside and outside the pipe,jet structure and energy conversion of high-pressure pulsed water jet under different nozzle structures are comprehensively analyzed.The conclusions of this paper are summarized,compared and verified,which provides a reference for further numerical calculation and theoretical analysis of high-speed pulsed water jet. |
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