Breakup of Aerated Liquid Jets in Subsonic Crossflow

Abstract

An experimental investigation of the breakup of an aerated-liquid jet in subsonic crossflow is described. The present test conditions were similar to those encountered in fuel injection in ramjet engines. Previous studies of spray structures of aerated-liquid jet in crossflow have been limited to the dilute spray area (downstream distance of greater than 100 jet diameters) using phase Doppler interferometry and along the liquid surface using wet holographic plates. The objective of the present study was to extend these earlier measurements to investigate the dense-spray near-injector region immediately downstream of the injector (0-50 jet diameters), in which secondary breakup may occur to bridge the gap between drop-size distributions along the jet surface and those obtained using phase Doppler interferometry in the far field of the injector. Three-dimensional microscopic digital holography was used to record and measure droplets sizes and locations within the three-dimensional volume of the spray. Earlier results of the primary breakup of aerated-liquid jets in crossflow show that the gas jet along the axis of the annular flow leaving the injector passage forces the annular liquid sheet into a conical shape that extends from the injector exit. Primary breakup occurs in a similar manner along both the upstream and downstream sides of the liquid jet (relative to the crossflow), which suggests relatively weak aerodynamic effects on the primary breakup. In the present study, the aerodynamic effects on the drop sizes in the wake region of the fuel injector were considered. The test conditions include different gas-to-liquid mass flow rate ratios and jet-to-freestream momentum flux ratios. The present measurements of the spray structure of aerated-liquid jets in crossflows shows a reduction in drop sizes with downstream distance that may be attributed to the drop secondary breakup.