LAUSR

Abstract A light field enhancement approach using a profiled window and a ray tracing method was developed to eliminate optical shadowed regions in particle image velocimetry measurements. In this approach, the profiled window was particularly designed to optimize the global illumination of tracer particles; the ray tracing method was employed to predict the illumination intensity of the light field and optimize geometry of the profiled window. To this end, two representative configurations featured by annoying optical shadows, including the internal intersection flow and external cylinder flow, were selected for demonstration. Preliminary measurements agreed with ray tracing analysis of the existing shadows; for the internal intersection flow and cylinder flow, a bi-arc window and a parallel bi-elliptic window were respectively proposed to guide the light sheet to illuminate the otherwise shadowed region. Finally, these two flows with profiled windows embedded in experimental configurations were measured, clearly capturing the unsteady vortex structures. The proposed light field enhancement approach along with high-precision machining and polishing techniques comprise a sophisticated strategy to eliminate optical shadows in particle image velocimetry measurements.