Synthetic Aperture Imaging of Turbulent Sheet Breakup and Ship Spray

This project aims to characterize the size range and spatial distribution of droplets formed by unsteady, turbulent sheet breakup, such as that formed by ship bow waves. Advanced high-speed imaging will be combined with emerging three-dimensional light-field imaging techniques to map droplet characteristics, including velocities to develop models and validate numerical codes. The synthetic aperture imaging is based on the light field imaging concept, which involves sampling a large number of light rays from a scene, using a camera array with 9-25 cameras, to allow for scene reparameterization using synthetic aperture refocusing. By reparameterizing the light field, one can focus on arbitrary focal planes throughout the scene and “see-through” partial occlusions. Measurements in densely seeded volumes are not possible with current 3D imaging techniques, which, for example, typically fail in bubbly flows with void fractions greater than 5-10%. The novelty of the approach presented herein is the application of the reparameterization methods to 3D spray imaging and the generation of algorithms to reconstruct 3D droplet fields from the refocused images.

MIT’s 3D synthetic aperture imaging velocimetry system represents the next generation of 3D imaging techniques and can have significant impact on the community due to the low cost of image reconstruction and the ability to resolve densely seeded flow fields, to image near deformed interfaces, and to see through partial occlusions.