Study On Jet Breakup In Non-uniform Air Crossflow Field

In this paper,the jetting characteristics and breakup process of the liquid jet in non-uniform air crossflow are studied by both experimental and numerical method.In terms of experiments,several experimental parts and facilities were designed and machined.They would enable observation of liquid jet breakup in shear-laden mode air crossflow and swirling air crossflow.A high-speed camera is utilized to capture and record the breakup process of the liquid jet.The images are processed by the binary method.In terms of numerical simulation,the standard k-?turbulence model is used to study the shear-laden mode crossflow without liquid jet in it.Meanwhile the airflow field is also analyzed as a reference for follow-up studies.The VOF coupled Level Set method is used to simualte the liquid jet breakup phenomenon in air crossflow.The numerical simulation results of shear-laden mode airflow showed that when the upper and lower inlet air flow velocity ratio?UR?is not equal to 1,a quasi-linear velocity distribution gradient would show up at the outlet downstream area,and there would form a shear layer.And air vortex would appear in the wake area.As the absolute value of UR increases or decreases from 1,the difference between the upper and lower inlet airflow velocity increases,it could be seen that the gradient of the shear layer augments,and the airflow vortex in the wake region becomes larger.With development,the distribution of air flow field lines is becoming more turbulent.The average Weber number We_avg,gvg,g has no obvious effect on the distribution of airflow.In the experimental study on the phenomenon of liquid jet breakup in shear-laden mode air crossflow,an obvious secondary bending of liquid jet could be observed at the middle vertical position of the jet test section.On the surface of the liquid column,the waves transformed from smooth shape towards first-order non-linear symmetry mode shape,spiral shape,and finally the column fractures.Refereing to the results of numerical simulation under corresponding operating conditions,it is found that the shear layer in the airflow field at the middle vertical position of the experimental section is strong,and the aerodynamic force affects the surface of the liquid jet in the form of strong shear force.On the cross-section of the fracture postion,the asymmetrical airflow vortex caused spiral surface wave and the surface wave finally contributes to the formation of the liquid bag.In the study of the injection characteristics of the jet,it is found that the jet penetration increases with the increase of the liquid-to-air momentum ratio q in all experimental conditions.There also exists a positive relationship between the jet penetration and UR.The average Weber number We_avg,g has no exact effects on the airflow.Liquid jet breakup in the swirling air crossflow was studied preliminarily via both experimental and numerical simulation methods.The trajectory of the liquid jet was fitted.In the weak swirling folw?SN less than 0.6?,it makes no significant difference on the liquid jet trajectory compared with it in uniform air crossflow.The jet penetration in the weak swirling air crossflow even increases.In the strong swirling flow?SN greater than 0.6?,the jet penetration would be suppressed.Refering to the numerical simulation results,it is found that in the strong swirling airflow,the size of the swirling zone even covers the liquid jet zone.It would result in the conversion of the partial kinetic energy of the liquid jet into the turbulent kinetic energy of the airflow,thus weakening the penetration.In the weak swirling flow,the size of the swirling zone is not grand enough and the aerodynamic force at the edge of the swirling zone is mainly radial,therefore it would help in promoting the penetration of the liquid column.At the same time,it can be found in the numerical simulation results that a negative pressure zone will be formed at the outlet of the cyclone,which can explain the phenomenon that the trajectory of the liquid column swings in the upstream direction.In conclusion,it can be inferred that when UR is greater than 1,the jet penetration is greater,and the time required for the liquid jet breakup is longer.When UR is less than 1,the jet penetration is less.The earlier breakup happens,the liquid jet atomization will be better in the same time.In addition,while studying on the condition of the breakup and atomization of the liquid jet in the swirling mode crossflow,it is necessary to consider both the strength of the swirler and the position of the nozzle.This would provide a certain guiding significance for the design and research work of the LDWI combustor.