Single-camera PTV within interfacially sheared drops in microgravity

Abstract

Development of experimental methods for in situ particle tracking velocimetry (PTV) is fundamental for allowing measurement of moving systems non-tailored for velocimetry. This investigation focuses on the development of a post-processing methodology for single-camera PTV, without laser-sheet illumination, tracking native air bubbles as tracer particles within a liquid drop of human insulin in microgravity. Human insulin functioned as a sufficiently complex, non-Newtonian fluid system for testing fluid measurement methodology. The PTV scenario was facilitated by microgravity technology known as the ring-sheared drop (RSD), aboard the International Space Station, which produced an optical imaging scenario and fluid flow geometry suitable as a testbed for PTV research. The post-processing methodology performed included five steps: (i) physical system characterization and native air bubble tracer identification, (ii) image projection and single-camera calibration, (iii) depth determination and 3D particle position determination, (iv) ray tracing and refraction correction, and (v) particle history and data expansion for suboptimal particles. Overall, this post-processing methodology successfully allowed for a total of 1085 particle measurements in a scenario where none were previously possible. Such post-processing methodologies have promise for application to other in situ PTV scenarios allowing better understanding of physical systems whose flow is difficult to measure and/or where PTV-specific optical elements (such as laser light sheets and dual-camera setups) are not permissible due to physical or safety constraints.