Dynamics of a radially expanding circular liquid sheet and its atomization characteristics

Abstract

The present study pertains to unsteady behavior of the radially expanding circular liquid (water) sheet that emerges from the lip of a cone-disc deflector subjected to the orthogonal liquid jet impingement from a nozzle. This test configuration is a simplified version of a pendent fire sprinkler head. The goal is to correlate the dynamical characteristics of the liquid sheet with those of the ligaments and droplets formed during its atomization. Time-resolved high-magnification imaging at kilohertz of framing rates is adopted for shadowgraphy, Mie scattering of high-repetition-rate laser sheet, and planar laser induced fluorescence (PLIF) of the liquid sheet is carried out for different Weber numbers over a range of 745 <Wejet < 2484. The threshold amplitude and growth rate of the radial Kelvin-Helmholtz wave until it shears abruptly over a narrow radial zone into ligaments are qualitatively reported. The radial and azimuthal wavenumbers are correlated with ligament length and thickness respectively. The relationship between ligament and droplet volumes Vdroplet = 0.5 Vligament specifies the disintegration of ligaments in to droplets. Further, the droplet diameter D10, ligament length Llig and ligament thickness tlig reveal that Llig >D10 >tlig for given conditions. The correlations of D10 and D32 with Wejet are obtained. Finally, the dependence of the droplet diameter on the discharge pressure is derived.