Fluid Flow Analysis On Relations Of Water Jet To Nozzle Structure

Jet flow performance is closely related to its ability and efficiency in cutting,cleaning etc.applications in engineering.Jet flow with high spreading means that its flow distance is short,and therefore decrease its impact force on target material.At present,there has not been theoretical method to optimize the design of a nozzle because of the lack of understanding of fundamental reasons of jet spreading caused by the flow in nozzle outlet section.Thus the present study is aimed at investigating the flow in a nozzle(e.g.conical nozzle)with various degree of contraction angles and cylinder section lengths and it's fundamental relations to jet performance.Numerical study has been conducted using 2D–dimensional axis-symmetric models.The flow is simulated using CFD(Fluent)software.Conical nozzles with variant geometry(i.e.contraction angle,length of outlet section)are used to do flow simulation on both nozzle-inside flow and its jet flow in order to analyze and build relations between flow in nozzle outlet section and jet flow with the aim at understanding of fundamental reasons or conditions for nozzle related jet spreading.Firstly this work consists of six nozzles with contraction angles of,5°,7°,10°,13°,15°,30°,and 60°in which these contraction angles were varied and their corresponding cylindrical section lengths(6mm)were fixed.Secondly the nozzle contraction angle of 13°was fixed and its corresponding cylindrical section lengths(d,2d,3d,4d and 5d)were varied,where by‘d'stands for nozzle outlet diameter.Thirdly the nozzle contraction of 13°and its corresponding cylindrical section length(6mm)were fixed but its corresponding outlet diameters(2.4mm,2.6mm,2.8mm and 3mm)were varied.Finally the nozzle contraction angle of 13°and its corresponding cylindrical section length(6mm)were fixed but its corresponding inlet pressures(40MPa,50MPa,60MPa,70MPa and 100MPa)were varied.The simulation results showed that,when the nozzle contraction angle is decreasing from60°to 7°,the boundary heights,turbulent intensities at the nozzle outlet section,are also decreasing,correspondingly the spreading angles of jets decrease and jet core lengths increase.When the cylindrical section length decreases from 5d to 1d,the boundary heights,turbulent intensities at the nozzle outlet section are also decreasing,correspondingly the spreading angles decrease and core lengths increase,the boundary height was ranging from0.19mm to 0.12mm,turbulent intensities ranging from 26.46%to 23.92%,spreading angles range from10.5°to 8.6°and the core lengths range from 21.90mm to 19.20mm,but the cylindrical section length 0.5d gave high boundary height and high turbulent intensity compared to 5d~1d.The optimal nozzle parameters obtained are as follows:contraction angle is 7°,cylindrical section length is 3 mm and nozzle outlet diameter is 3mm.Under these optimal nozzle parameters,the nozzle has the best outlet section flow with boundary height0.10mm,turbulent intensity 22.09%,spreading angle 8°and core length 23mm of jet.As to the influence of nozzle cylindrical section,simulations have shown that,the maximum outlet velocity of the nozzle with cylindrical section is higher than that of the nozzle without cylindrical section,for instance nozzle of 13°with cylindrical section length its maximum velocity decreased by 0.108)?that with 30°decreased by 0.128)?,and for 60°decreased by0.138)?The maximum turbulent intensity at nozzle outlet section is decreasing when the pressure drop is decreasing and the boundary heights(0.2mm)remain constant as the pressure drop decrease.At small pressure drop the outlet velocity is decreasing and at higher pressure drop the outlet velocity is increasing,for instance 100MPa gave the velocity of 4.79×10~28)?and 70MPa gave the velocity of 3.89×10~28)?etc.