Applications of Plenoptic PTV: A Single-Camera Time-Resolved Three-Dimensional Fluid Flow Measurement Technique

Abstract: When conducting experiments in fluids that attempt to measure the local velocity of a fluid, most modern approaches involve imaging seed particles present in the fluid. The current state of the art uses multi-camera approaches such as tomographic particle image velocimetry (TOMO-PIV) and, more recently, particle tracking algorithms such as "Shake-The-Box" to obtain all three components of velocity in three dimensions (3D3C). However, multi-camera approaches are generally limited to use in macroscopic cases where the positioning of the cameras is possible and even in these cases obtaining and maintaining proper camera orientation can be time-consuming. These challenges are exacerbated when attempting mini- or micro-scale imaging, where aligning all four cameras to image the same volume can be all but impossible. Using plenoptic imaging, a single camera can encode information about 3D space onto a 2D CCD. This approach is viable as a simple 3D3C method in macroscale experiments and could be invaluable as a 3D3C tool in mini- and micro-scale experiments where only a single route of optical access is available. The present work focuses on conducting mini-scale experiments using a commercial multi-focus plenoptic camera (R5, Raytrix GmbH) with commercial plenoptic image processing software (RxLive 2.01, Raytrix GmbH) to perform time-resolved 3D3C particle tracking velocimetry (PTV) using an in-house developed code (in Matlab R2015b).