Impact of the shearing action of swirling flows on droplet breakup in a hybrid airblast nozzle with different dual swirler configurations

The hybrid airblast nozzle exploits aerodynamic forces to improve the atomization characteristics. This study investigated the effects of the swirler vane angles and rotational configuration on spray angle and small droplet generation in the shear layer. Particle image velocimetry and Phase–Doppler particle analyzer were used to measure the spray characteristics, and droplet size and velocity. The swirling airflow field was measured using tracer particles. The results showed that increasing the swirler vane angle and using the co-rotation configuration (“co-rotation”) increased the spray angle. The swirling airflow field in the counter-rotation configuration (“counter-rotation”) showed higher turbulence kinetic energy (TKE) and Reynolds stress than co-rotation within the shear layer. Under co-rotation, a strong recirculation zone formed in the central region, causing high relative velocity between the swirling airflow and spray. However, in the shear layer, many small droplets produced by the high relative velocities between the two swirling airflows of counter-rotation were entrained within the recirculation zone, and moved toward the spray center. In consequence, in the spray center region, the SMD for counter-rotation was smaller than that for co-rotation. The results confirmed that the strong shearing action produced by the rotational direction is another important factor influencing the secondary breakup characteristics.