Spatial drop behavior of a rotary atomizer in a cross flow

This paper presents an investigation of the spatial droplet distribution around a rotary atomizer in an air cross flow. The droplet size, velocity, and spray distribution were measured using a phase Doppler particle analyzer system. The spray was photographed using a high-speed camera. The rotary atomizer was driven at speeds of 5000 rpm, 10,000 rpm, and 15,000 rpm. The fuel flow rate was held constant at 15 kg/h, and the air cross-flow velocities varied from 25 m/s to 150 m/s. The overall spray shape was observed to shrink toward the axis of rotation with increasing cross-flow speeds. High-speed visualization showed that the injected ligaments disintegrate into fairly large droplets and spread out in the radial direction at lower cross-flow velocities. At higher cross-flow speeds, the injected ligaments are abruptly deflected and broken up in the downstream direction close to the surface of the atomizer and are mixed with the cross-flow air stream immediately. The axial velocity profile indicates that a strong recirculation zone is formed just below the rotating nozzle. A high tangential velocity is shown to exist close to the injection point. Further downstream, the radial velocity component is shown to be dominant, while the tangential velocity becomes weak. The axial velocities show similar trends for the same cross-flow velocities, as the droplets follow the dominant air stream formed by the cross flow regardless of rotational speed. Near the injection orifice, relatively larger droplets are concentrated in a narrow region close to the radius of the atomizer. As the liquid jet travels downstream, the droplets are dispersed by the cross flow and distributed over a wider area. The cross flow influences the Sauter mean diameter directly; however, the rotational speed of the nozzle only has a large effect on the spray at slower cross-flow conditions. This injector design is shown to have a circumferential uniformity of ±4 μm, making it an acceptable choice for combustion applications.