Experimental Study On Spray Characteristic Of Liquid Jet In Ma2.1 Supersonic Crossflow

The present research focused on the spray characteristics of liquid jet in Ma 2.1 supersonic crossflow.Droplet diameters and droplet velocities were investigated experimentally.In the research,the optical measurement Particle Dynamics Analysis(PDA)was employed to obtain the spray characteristics of the liquid jet in supersonic crossflow,without disturbance to the flow field.The instability of Sauter Mean Diameter(SMD)calculation caused by limited sampling was investigated first.The effect of large diameter droplets on the calculation of SMD was analysed in the jet atomization of supersonic crossflow.Probability threshold method was introduced to eliminate the effect of large diameter droplets based on the analysis.Result showed that,the probability threshold method was of avail to the study of spray droplets distribution and was used in the latter study.Deep analysis of spray droplet diameters was carried out.The initial SMD distributions and the distributions after probability threshold method along lengthwise and streamwise were obtained.Results showed that the distribution of SMD along lengthwise is of C type.Further study showed that,the smallest droplet diameter located in the region y/h=0.7.The large droplets in the near wall region were sheared off from the jet and spread to the whole spray area.SMD along streamwise get smaller first then remain stable.The log-logistics distribution fitted the experimental results best.The atomization process along streamwise can be divided into three regions,initial atomization region with amount of large droplets,twice atomization region with decrease of large droplets and the region with little atomization.With the help of gas,the spray becomes more uniform.Large droplets existing in the far field of spray affect the uniformity of droplet distribution.The effects of two factors,more exactly the pressure drop of liquid jet and the diameter of the injector,on the spray characteristics were investigated by PDA technique in detail.The experimental results indicate that with the increase of pressure drop,the droplet diameter of the jet near field increase obviously,while the change is not obvious in the far field.With the decrease of injector diameter,the droplet diameter decrease,leading to a more uniform diameter distribution and promoting the atomization process to a large extent.The results showed us that the pressure drop and injector diameter have little effects on the droplets longitudinal velocity.Dimensionless analytical method was used to obtain the empirical relationships between the droplet diameters with the working condition parameters,and compared with the experimental results.