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. This 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 1,085 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 lights sheets and dual camera setups) are not permissible due to physical or safety constraints.