Compressible Flow Structure of Droplets Under Supersonic Conditions

Abstract

The compressible flow structure in front of deforming droplets in a continuously accelerating supersonic flow was examined in a draw-down supersonic wind tunnel which allowed relative velocities as high as Mach 1.8. 100-micron diameter droplets were generated upstream of the tunnel entrance using a Droplet-On-Demand generator. Direct backlit and schlieren imaging were performed in order to verify the experimental configuration and image the shock structure, respectively. The test liquid employed was 2-propanol due to its non-volatile nature and ease of injection. Theoretical predictions provide a first order approximation for several bow shock parameters. The schlieren images were processed to highlight the droplet and bow shock structure. Measurements of blurred shock thickness and Mach angle were found to be generally consistent with theoretical predictions. The time scales of shock formation and shock reaction to droplet deformation were estimated to be much less than the time scale associated with droplet breakup.