关键词: 自激扫掠喷嘴, 扫掠张角, 扫掠形态, 雾化特性, 康达效应

Abstract: This study systematically investigated the influence of the outlet expansion section geometry angle A of a self-excited sweeping nozzle on jet characteristics, such as sweeping angle α, sweeping morphology, and atomization performance. Preliminary studies were first conducted on the influence of outlet geometry angles across a wider range of outlet geometry angles (A=50°~110°、0°) under an enlarged scale (inlet throat width WT = 2.5 mm). Subsequently, detailed experiments were carried out at a realistic submillimeter scale (WT = 0.5 mm) using selected typical angles. The external jet characteristics and droplet size distribution were measured using high-speed shadowgraphy and a Malvern laser particle size analyzer, respectively. Results indicate that the outlet geometry angle A of the self-excited sweeping nozzle significantly affects both the sweeping angle α and sweeping morphology. When the self-excited sweeping nozzle has no outlet expansion section, the sweeping angle formed by the nozzle flow channel in the natural jet state is α0. When A is slightly bigger than α0, under the Coanda effect, the jet attaches to the wall of the outlet expansion section, putting the jet in an attached state, resulting in a sweeping angle α close to A and forming a quasi-trapezoidal sweeping morphology, accompanied by stretched liquid films and residual liquid ligaments. A given nozzle configuration under specific operating conditions exhibits a maximum attainable sweeping angle αmax. When A exceeds αmax, the Coanda effect ceases to function, causing the jet to detach from the influence of the expansion section wall. The sweeping angle then reverts to α0, forming a quasi-S-shaped sweeping morphology, with a main-secondary angle structure emerging at higher pressure drops. The atomization droplet size distribution is also influenced by the sweeping morphology. Under the quasi-trapezoidal sweeping morphology, droplet sizes are larger near the two lateral boundaries and smaller in the central region. Conversely, the quasi-S-shaped sweeping morphology promotes more uniform jet breakup, and the variation range of the droplet size in the spanwise direction is smaller. This study reveals the influence patterns and underlying mechanisms of the outlet geometry angle on the spray characteristics of self-excited sweeping nozzles, providing a theoretical basis for their optimized design.

Key words: self-excited sweeping nozzle, sweeping angle, sweeping morphology, atomization characteristics, Coanda effect