Cavitation in a Two-Dimensional Nozzle and Liquid Jet Atomization (1st Report, Ultra-High Speed Visualization)

Abstract

Cavitation and internal flow in the nozzle of a liquid injector are known to affect the atomization of a discharged liquid jet. In the present study cavitation in a two-dimensional (2D) nozzle and the injected water jet were visualized using an ultra high-speed camera. As a result, the following conclusions were obtained : (1) The behavior of cavitation in the 2D nozzle and liquid jet agreed qualitatively with the previous observations of cylindrical nozzles. (2) When the cavitation number σ was1.18, the inception of small cavitation bubbles was observed near the nozzle inlet apart from the side wall. (3) The number of cavitation bubble clouds increased with decreasing of σ (0.75≤ σ<1.18), and the streamwise length of the cavitation region increased toward the middle of the nozzle (developing cavitation). The bubble clouds were clearly observed to recirculate in the separated boundary layer. In the case a wavy jet was observed with no significant effects of cavitation on liquid jet atomization. (4) With a slight decrease of σ from0.75, the cavitation region suddenly extended to the nozzle exit (super cavitation). The shape of the cavitation region near the inlet became smooth, which imply the formation of a long cavitation bubble near the inlet. At the downstream half of the nozzle, clouds of cavitation appeared and collapsed intermittently within the nozzle. In the case atomization was promoted to form spray with ligaments and droplets.