| Pre-mixed waterjet shot peening surface modification technology is a metal workpiece surface treatment technology with broad application prospects.It has the advantages of high energy density and concentration,wide modification range and so on.The modification effect depends on the distribution of jet beam energy field,which is closely related to the shot velocity distribution.At present,there are still theoretical and experimental validation problems in the study of shots velocity distribution of premixed waterjet,resulting in the failure to obtain a more accurate analytical or numerical solution for the velocity distribution characteristics of the jet,which affects the determination of coverage and target distance in subsequent engineering applications.This thesis uses a combination of numerical simulations and experiments to study the shots velocity distribution in a pre-mixed waterjet,and analyzes the influence law of various parameters on the shots velocity.Based on the above,the main researches are as follows:Firstly,the numerical simulation of pre-mixed waterjet was carried out.Based on the VOF-DEM coupling method,the three-phase flow of the internal and external flow fields of the pre-mixed waterjet nozzle was simulated.Considering the shot collision,the bidirectional coupling of momentum and energy exchange between particles and fluid was realized.Secondly,the pre-mixed water jet injection system was designed and built,and the basic parameters of the jet flow process were determined through experiments,which provides data support for the subsequent simulation model construction.The experimental results show that the nozzle inlet pressure has a stabilization period during the pre-mixed waterjet injection process,and the shots mass flow rate and mixing ratio remain basically the same during the pressure stabilization period;the mixing ratio does not change significantly with the change of the nozzle inlet pressure,and the mixing ratio can be adjusted by adjusting the damping ratio.Thirdly,based on the knowledge of fluid mechanics,the theoretical formula of shot mass flow rate was deduced and verified by experiments.The results show that the difference between the theoretical value and the simulated value is within 8%,which verifies the correctness of the theoretical formula and provides a basis for obtaining the shot mass flow under different working conditions.Fourthly,the shots velocity distribution in the pre-mixed waterjet was tested experimentally using a pre-mixed water jet PIV special test bench,and the experimental results were compared with the numerical simulation results.The results show that the difference between the experimental and simulation results is less than 5%,which verifies the correctness of the simulation modeling.Finally,based on the CFD-DEM coupling method,a series of simulation studies under single factor conditions were carried out,and the analytical empirical formulas of the maximum shot velocity and the nozzle inlet pressure were obtained,as well as the variation law of the shot velocity with various factors.The results show that the maximum shots velocity in the pre-mixed waterjet increases with the increase of nozzle inlet pressure and nozzle outlet diameter,and decreases with the increase of mixing ratio,shot diameter,shot density,nozzle aspect ratio and nozzle cone angle.In this thesis,the shot velocity distribution law in the external flow field of the pre-mixed waterjet nozzle and the influence law of flow parameters,shot parameters and nozzle structure parameters on the shot velocity distribution are obtained,which is of certain guiding significance to reveal the mechanism of surface modification by premixed water jet,improve the surface modification capacity and develop the modification process parameters. |
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