Study On Spray Characteristic Of Liquid Jet With A Cavity In Supersonic Crossflow

The present research focused on the cavity effects on spray characteristics of liquid jet in supersonic crossflow.The liquid jet break-up position,jet penetration and spray velocity distribution were investigated experimentally.In the research,the optical measurement Pulsed Laser Background Imaging Method,high speed camera and Particle Image Velocimetry(PIV)were employed to obtain the spray characteristics of the liquid jet in supersonic crossflow.Firstly,the first break-up position was experimentally investigated.Geometric parameter of nozzle,diameter and length-diameter ratio,as the main influence factor was studied.Based on the experimental data and analysis,empirical correlation of longitudinal break-up position and liquid-gas momentum flux ratio,was obtained,containing the length-diameter ratio.Results show that,the break-up positions distribute at between 3d-12 d,where d is the nozzle diameter.Streamwise and longitudinal break-up distance increase with the liquid-gas momentum flux ratio increasing in supersonic crossflow.At the same jet pressure drop,streamwise and longitudinal break-up distance increase with the length-diameter ratio increasing,while with the diameter decreasing,streamwise break-up distance decreases longitudinal break-up distance increases.Secondly,based on the study of wall jet penetration and break-up position,the geometric parameter of the cavity was designed and 5 nozzles were distributed at the center line of the upstream cavity.High speed camera was used to recorded the liquid jet images.Cavity effects on jet penetration can be described that reducing the jet penetration at the inlet and lifting the penetration at the outlet of the cavity.Jet position and jet pressure drop were two main factors influencing the cavity effect.A lower pressure drop helps enhance the cavity effect.A specific jet position,3D(where D is the cavity depth)was found that the jet penetration reached to the lowest level at the cavity inlet.This is because in the one hand the far jet position lengthens the accelerating distance,leading to spray entering the cavity difficulty.In the other hand,if the jet position gets too close to the cavity,a higher longitudinal velocity makes it hard for droplets entering the cavity.Thirdly,the PIV experiments were conducted to study the cavity on the spray velocity distribution.Results indicate that the streamwise velocity can be divided in to three parts.The boundary streamwise velocity can reach the 90% of the crossflow velocity and stay steady downstream.The middle spray velocity experiences acceleration,deceleration and re-acceleration processes.The bottom spray velocity,also in the cavity,decreases downstream.Similarly,jet pressure drop and jet position were also studied.Results indicate that increasing the pressure drop contributes to reduce the spray velocity in the cavity,while it may lower the quantity of droplets entering the cavity according to the jet penetration analysis.With the distance of the nozzle to the cavity increasing,the spanwise spray area over the cavity is enlarged.Therefore,high jet pressure drop and specific jet position contribute to form low-speed backflow zone in cavity.