Spray Trajectories of Liquid Fuel Jets in Subsonic Crossflows

Abstract

Spray trajectories of liquid jets injected into a subsonic crossflow were experimentally studied and correlated with jet operating parameters. The spray dynamics are known to be different in the three spray regimes: the column, the ligament, and the droplet regimes. Trajectory correlations were therefore developed for the column and droplet regimes separately in an effort to gain a better understanding of the flow dynamics. A previously obtained column trajectory correlation was tested against results from other studies; the comparison indicates that the trajectory can be predicted based on consideration of aerodynamic acceleration. However, the trajectory may be affected by variations in incoming air velocity profiles, boundary layer thickness, and injector passage design. Experimentally obtained spray trajectories were correlated using simplified momentum equations of a spherical droplet in an air flow. Correlations of droplet locations, velocities, and drag functions at the upper spray boundary were obtained. Results suggest that droplet sizes decrease as the air freestream velocity increases, and they are independent of liquid property variations. At x/d = 150, the droplets at the upper spray boundary always have an axial velocity of 70% of the air freestream velocity and a transverse velocity of 51 % of the injection velocity. Predictions based on the correlations obtained are in fair agreement with measured values. The correlations obtained in this study provide not only the location of the spray boundary, but also droplet sizes and velocities.