Placement and Acceleration of Liquid Jets in Pressurized Cross-flows

Determination of velocities and locations of liquid droplets formed during the atomization process of a liquid jet injected in a high-pressure air cross flow represents an essential step in the definition of appropriate boundary conditions for the elaboration and validation of reliable numerical models. In this paper, three test cases relative to different air-to-liquid velocity ratios and air temperatures are analyzed by means of elastic scattering imaging and particle image velocimetry (PIV). The significance of the PIV measurements, evaluated as a function of spatial position and operating conditions, was adequately high with the exception of the nearest field to the injection point, where the spray is too dense. Velocity data, measured in the axial and transversal planes, are presented along with corresponding velocity components' profiles at selected positions. Results show the rapid alignment of droplet trajectories to the airflow and the dominant role played by the airflow in determining final droplet velocities and, hence, their placement in the spray plume. The droplets close to the windward profile move parallel to the jet leading edge, whereas in the leeward region they cross the scattering intensities' isocontours. On the grounds of these results, a synthetic description of liquid droplet velocities' behavior in the different regions of the spray plume is given that represents a useful conceptual tool in the attempt to correlate physical mechanisms, underpinning atomization processes, to the observed phenomenologies.