CHARACTERIZATION OF TIME-AVERAGED AND TEMPORAL TWO-PHASE FLOW STRUCTURES IN AERATED-LIQUID JETS USING X-RAY DIAGNOSTICS

摘要

The structure of the two-phase flow inside the nozzle of an aerated-liquid injector and in the near field of the discharged plumes was experimentally explored with synchrotron x-ray diagnostics, including x-ray radiography, x-ray fluorescence, and x-ray high-speed imaging. One axisymmetric beryllium aerated-liquid injector featuring the inside-out aerating scheme was fabricated to mate with three aerating tube designs for the creation of two-phase flows. Water and nitrogen were doped with x-ray fluorescent elements at low concentrations to facilitate the x-ray diagnostics. Quantitative time-averaged liquid mass distributions for the two-phase mixture were successfully obtained from both radiography and fluorescence measurements. Averaged flow properties, such as liquid density and liquid velocity, at various cross-sections, were also derived from these measurements. Temporal formation and evolution of the two-phase mixture inside the aerated-liquid injector were also characterized with high-speed imaging. It was found that an annular flow is typically created in the two-phase mixture near the nozzle exit, despite the complex fluid dynamics in the liquid/gas interaction, flow passage volume change, and recirculation zone. The two-phase flow structures in the nozzle and the spray regions created from the present injector and aerating tube configurations are highly similar for a given injection condition. The major factor contributing to the similarity of the two-phase flow structures in the two regions may be the large area contraction ratio between the mixing chamber and the nozzle passage, which leads to a significant increase in flow speed and thus to aerodynamic stretching of the two-phase flow into fine structures.