Laser Sheet Dropsizing of Ethanol Jets in Supersonic Crossflows With Far Field Oblique Shocks

Abstract Uniform mixing of a liquid injectant into a high momentum flux gaseous flow constitutes a significant engineering challenge with valuable applications. This study characterizes the Sauter mean diameter (SMD) of an ethanol jet in supersonic crossflow and the use of an oblique shock to enhance atomization of the far field plume. Momentum flux ratios of the injectant vary from 0.7 to 7.3 and correspond to the catastrophic breakup regime with Weber numbers above 5000. A baseline converging diverging flow path with a 25.4 mm throat height is installed in a blow-down wind tunnel to produce a Mach 2 air flow, and a 6° ramp is included to produce an oblique shock that impinges the spray 15 cm downstream of the injector. Plain orifice injectors of 1 and 2 mm diameter are used to inject ethanol. In the axial plane, a simultaneous Mie scatter-Laser induced fluorescence imaging technique is used to measure contours of SMD. A calibration of this technique is conducted with simultaneous phase doppler interferometry measurements, and the convergence characteristics of the mean SMD and signal to noise ratio are computed for every test case. The dynamic behavior and interplay between the injection bow shock, the spray, and the impinging oblique shock is studied through schlieren imaging, and its effect on the droplet size is compared with the baseline configuration.