A computational fluid dynamics(CFD)study of the impact characteristics and stagnation formation on a solid target surface by an abrasive waterjet at supersonic velocities is presented to understand the impact process....A computational fluid dynamics(CFD)study of the impact characteristics and stagnation formation on a solid target surface by an abrasive waterjet at supersonic velocities is presented to understand the impact process.A CFD model is developed and verified by experimental water and particle velocities and then used to simulate the jet impact process.The trends of the stagnation formation and its effect on the jet flow with respect to the jetting and impacting parameters are amply discussed.It is found that stagnation formation at the impact site increases with an increase in the impact time,nozzle standoff distance and nozzle diameter,while the initial peak velocity at the nozzle exit has little effect on the size of the stagnation zone.It is shown that stagnation markedly changes the water and particle flow direction,so that the particle impact angle is varied and the jet impact area is enlarged.The jet structure may be classified to have a free jet flow region,a jet deflection region with a stagnation zone and a wall jet region.Furthermore,the stagnation affects significantly the waterjet and particle energy transferred to the target surface.The average particle velocity across the jet is reduced by approximately one third due to the damping effect of the stagnation under the conditions considered in this study.展开更多
Soft abrasive flow（SAF） finishing can process the irregular geometric surfaces, but with the matter of low processing efficiency. To address the issue, an improved SAF finishing method based on turbulent kinetic ene...Soft abrasive flow（SAF） finishing can process the irregular geometric surfaces, but with the matter of low processing efficiency. To address the issue, an improved SAF finishing method based on turbulent kinetic energy enhancing is proposed. A constrained flow passage with serration cross-section is constructed to increase the turbulence intensity. Taking the constrained flow passage as the objective, a two-phase fluid dynamic model is set up by using particle trajectory model and standard k-ε turbulence model, and the flow field characteristics of the flow passage are acquired. The numerical results show that the serration flow passage can enhance the turbulence intensity, uniform the particles distribution, and increase the particle concentration near the bottom wall. The observation results by particle image velocimetry（PIV） show that the internal vortex structures are formed in flow passage, and the abrasive flow takes on turbulence concentrating phenomenon in near-wall region. The finishing experiments prove that the proposed method can obtain better surface uniformity, and the processing efficiency can be improved more 35%. This research provides an abrasive flow modeling method to reveal the particle motion regulars, and canoffer references to the technical optimization of fluid-based precision processing.展开更多
基金The project was financially supported by the Australian Research Council(ARC)under the Discovery-Projects scheme.K T would like to thank the Royal Thai Government for providing a PhD scholarship for this study.
文摘A computational fluid dynamics(CFD)study of the impact characteristics and stagnation formation on a solid target surface by an abrasive waterjet at supersonic velocities is presented to understand the impact process.A CFD model is developed and verified by experimental water and particle velocities and then used to simulate the jet impact process.The trends of the stagnation formation and its effect on the jet flow with respect to the jetting and impacting parameters are amply discussed.It is found that stagnation formation at the impact site increases with an increase in the impact time,nozzle standoff distance and nozzle diameter,while the initial peak velocity at the nozzle exit has little effect on the size of the stagnation zone.It is shown that stagnation markedly changes the water and particle flow direction,so that the particle impact angle is varied and the jet impact area is enlarged.The jet structure may be classified to have a free jet flow region,a jet deflection region with a stagnation zone and a wall jet region.Furthermore,the stagnation affects significantly the waterjet and particle energy transferred to the target surface.The average particle velocity across the jet is reduced by approximately one third due to the damping effect of the stagnation under the conditions considered in this study.
基金Supported by National Natural Science Foundation of China(Grant Nos.51375446,51575494)Zhejiang Provincial Natural Science Foundation of China(Grant Nos.LR16E050001,LZ14E050001)
文摘Soft abrasive flow（SAF） finishing can process the irregular geometric surfaces, but with the matter of low processing efficiency. To address the issue, an improved SAF finishing method based on turbulent kinetic energy enhancing is proposed. A constrained flow passage with serration cross-section is constructed to increase the turbulence intensity. Taking the constrained flow passage as the objective, a two-phase fluid dynamic model is set up by using particle trajectory model and standard k-ε turbulence model, and the flow field characteristics of the flow passage are acquired. The numerical results show that the serration flow passage can enhance the turbulence intensity, uniform the particles distribution, and increase the particle concentration near the bottom wall. The observation results by particle image velocimetry（PIV） show that the internal vortex structures are formed in flow passage, and the abrasive flow takes on turbulence concentrating phenomenon in near-wall region. The finishing experiments prove that the proposed method can obtain better surface uniformity, and the processing efficiency can be improved more 35%. This research provides an abrasive flow modeling method to reveal the particle motion regulars, and canoffer references to the technical optimization of fluid-based precision processing.
