Structured light-field focusing for flowfield diagnostics

Abstract

A novel structured light-field focusing system is developed for flowfield measurements and visualization. The imaging technique provides true planar, two-dimensional, refractive measurements of flow structures. The innovative method is based on the light-field principle and multiple light sources to structure the two-dimensional planar focused imaging. The system is further unique in that it provides velocity fields from particles at extreme sampling rates (>15kHz) driven by the forward scatter relative to traditional particle image velocimetry (PIV) systems. The arrangement and characteristics of the system are presented. The method has also been used to visualize an under-expanded free jet and impinging jet. The technique is demonstrated on various flows including spray imaging and velocimetry at high acquisition rates to characterize the performance of the diagnostic system. Additionally, the limits of the system have been demonstrated as a method for micro-scale visualizations and dense medium imaging. The study developed a formulation for using the optical diagnostic technique. The optical system parameters can be tailored to drive a shallow depth of field. Detail optimization of the diagnostic technique to achieve shallow range depth of field at a high signal to noise ratios is discussed. Finally, design considerations are proposed which will be pertinent in future, large-scale experiments.