Impact of wall film thickness on the spray atomization characteristics with varying pressure-swirl nozzle positions in hybrid airblast atomizers

This work examines how variations in liquid film thickness on the Venturi influence the spray atomization characteristics, with changes in the position of the pressure-swirl nozzle in hybrid airblast atomizers. By removing around 83 % of the Venturi circumference, the impingement behavior of spray droplets against the Venturi wall was captured, and image analysis techniques were employed for the quantitative measurement of the accumulated liquid film thickness on an acrylic plate. Droplet velocity and size distributions were measured using a Phase Doppler Particle Analyzer (PDPA). The impinged droplets on the Venturi surface displayed notable splashing and film buildup behaviors. In the absence of swirling airflow, the average flow velocity of the accumulated liquid film was determined. Using these measurements, the proportion of the liquid film formed on the plate relative to the injection flow rate (case 2) was compared to the predicted outcome (case 1). Discrepancies between case 1 and case 2 ranged from 24 % to 32 %. With an increase in the non-dimensional distance (h*), the angular momentum of the swirling airflow traversing the inner swirler was reduced as a result of friction with the wetted surface. In contrast, the effect of the swirling airflow passing through the outer swirler on spray increased, resulting in a wider spatial dispersion of the spray and a larger recirculation zone. Therefore, smaller droplets within the shear layer region increased while both the liquid film and the rim built up substantially at the Venturi, resulting in thicker accumulation.