Three-Dimensional Synthetic Aperture Imaging and Resolution of Multi-Phase Flows

Three-dimensional multiphase fluid flows demand advanced and innovative measurement systems in order to fully resolve the flow physics. Dense bubbly multiphase flows cannot be readily imaged by traditional, non-invasive flow measurement techniques due to the bubbles occluding optical access to the interior regions of the volume of interest. We present a novel technique for imaging these flows, which allows for determination of the 3D bubble distribution and bubble sizes despite the imaging challenges. By using synthetic aperture (SA) refocusing we are able to reparameterize images captured by an array of cameras to reconstruct a 3D volumetric map of the bubble field for every time instance. The SA refocusing technique has the unique ability, over conventional imaging methods, to see-through partial occlusions in the scene due to the configuration of the camera array and reconstruction algorithms, making it an ideal tool for resolving multiphase flows. Relatively dense bubbly flows can be resolved with good accuracy. We present fundamentals of the synthetic aperture methodology, a feature detection algorithm for extracting bubble size and location, and results from application of the technique to a bubble-entraining plunging jet.