INFLUENCE OF UNSTEADY BOUNDARY LAYER GROWTH BEHIND A NORMAL SHOCK WAVE ON THE DYNAMICS OF SPHERICAL WATER DROPLETS ON A SHOCK TUBE WALL

Abstract

The discrete increase of local pressure and temperature caused by a shock wave passing over a certain location in a shock tube allows for many potential investigations of the process of combustion. One of these investigations is the aero breakup of a liquid droplet, which could be a fuel droplet, and the instantaneous temperature rise results in potential combustion of the broken up fuel droplet. A specific study in how a wall-laden droplet breaks up in different freestream unit Reynolds number, diameter, and droplet attachment angle was conducted in order to characterize the different potential breakup modes seen by the aerobreakup of a droplet. Pointwise pressure data was employed to obtain freestream conditions, and shadowgraphs capturing the temporal evolution of the aerobreakup of a droplet on a shock tube wall in region 2 of a shock tube was observed. Edge detection was employed to quantify the droplet’s deformation over time. It was observed that lower freestream Reynolds number and larger droplet diameters delayed the breakup of the droplet, despite being at comparable Weber numbers. The attachment angle also impacted the rate of deformation. Instabilities on the upstream side of the droplet were observed to generally decrease with an increase of diameter. These trends were observed for all possible conditions.