Digital Holography for Investigating Front-Edge Instabilities of Liquid Jets in Supersonic Crossflows

Direct injection studies of liquid jets in supersonic crossflows are critical for understanding combustion in scramjet engines. Exploring these fluid dynamic interactions is not only an important step towards characterizing fundamental liquid breakup properties but also key for improving engine design. Understanding instabilities and primary breakup modes, for example, can contribute to improved steady power output, reduced NOx emission, and increased efficiency. Previous studies in the literature have examined how supersonic crossflows affect gaseous and liquid jet breakup characteristics using backlit imaging or schlieren techniques. In this work, we aim to study jet instabilities and droplet breakup characteristics using digital in-line holography. Experiments are conducted with a heated Mach 1.71 crossflow and a transitional regime liquid jet (slenderness ratio L/D of 19) with a diameter of 0.5 mm. High-speed and high-resolution digital in-line holography and schlieren methods are utilized to spatially resolve the jet breakup characteristics near the injection point. By analyzing the time-resolved data of the column instabilities, validation data can be obtained to help improve mathematical models, optimize injector geometry, and refine scramjet engine designs.