Dynamic Ballistic Imaging: A technique to measure acceleration in the spray formation region

Paper in proceeding, 2015

There is a need to acquire quantitative data from the spray formation (primary breakup) region of atomizing sprays. Such data would increase understanding of the dynamics governing breakup and provide a means to validate computational codes. To probe this region, however, is very challenging. One reason is the droplet cloud that surrounds it. This cloud effectively scatters light at optical wavelengths and can thus prevent larger fluid structures in the interior from being probed. Ballistic imaging is a technique, often used in a trans-illumination scheme, designed to mitigate the effects of scattering from the droplet cloud with the use of specialized optical filtering techniques. The resulting ballistic images are composed of the fraction of the incident light that retains image information from inside the spray. Consequently, it can reveal larger fluid structures and interfaces from the interior of this region and thus provide information on primary breakup. In this paper we discuss the implementation of a ballistic imaging system capable of acquiring three ballistic images in rapid succession with a well-defined time separation. Using image correlation velocimetry techniques on the image triplet, two dimensional velocity and acceleration fields of the primary breakup region can be obtained.