Three-dimensional synthetic aperture particle image velocimetry

Abstract

We present a new method for resolving three-dimensional (3D) fluid velocity fields using a technique called synthetic aperture particle image velocimetry (SAPIV). By fusing methods from the imaging community pertaining to light field imaging with concepts that drive experimental fluid mechanics, SAPIV overcomes many of the inherent challenges of 3D particle image velocimetry (3D PIV). This method offers the ability to digitally refocus a 3D flow field at arbitrary focal planes throughout a volume. The viewable out-of-plane dimension (Z) can be on the same order as the viewable in-plane dimensions (X-Y), and these dimensions can be scaled from tens to hundreds of millimeters. Furthermore, the digital refocusing provides the ability to 'see-through' partial occlusions, enabling measurements in densely seeded volumes. The advantages are achieved using a camera array (typically at least five cameras) to image the seeded fluid volume. The theoretical limits on refocused plane spacing and viewable depth are derived and explored as a function of camera optics and spacing of the array. A geometric optics model and simulated PIV images are used to investigate system performance for various camera layouts, measurement volume sizes and seeding density; performance is quantified by the ability to reconstruct the 3D intensity field, and resolve 3D vector fields in densely seeded simulated flows. SAPIV shows the ability to reconstruct fields with high seeding density and large volume size. Finally, results from an experimental implementation of SAPIV using a low cost eight-camera array to study a vortex ring in a 65 × 40 × 32 mm 3 volume are presented. The 3D PIV results are compared with 2D PIV data to demonstrate the capability of the 3D SAPIV technique.

Imaging Flow Velocimetry with Laser Mie Scattering

“…A high-speed system that combines the tomographic and holographic approaches was reported by Buchmann et al in 2013 [122]. Furthermore, volumetric PIV measurements with a light-field camera form part of ongoing research [123][124][125][126]. A high-speed system based on light-field PIV is a topic for future research.…”

Multiple-plane particle image velocimetry using a light-field camera

“…Techniques using volumetric illumination are: holographic PIV [2], tomographic PIV [9], defocussing PIV [10], astigmatism PIV [11] and synthetic-aperture PIV [12].…”

“…Light-field imaging was introduced to fluid mechanics as synthetic-aperture particle image velocimetry (SAPIV) [12]. The name is retained in this work.…”

Three-Dimensional Particle Image Velocimetry Using a Plenoptic Camera

“…Four techniques that have received attention for their ability to conduct 3-D, 3-C measurements are defocusing PIV, 5,6 holographic PIV, 7 tomographic PIV, 8 and synthetic aperture PIV. 9 The former is based on the use of specialized apertures near the camera lens or multiple cameras which eliminates the ambiguity in particle depth that occurs when a particle is not located within the focal plane. Computational algorithms use the knowledge of the aperture shape or camera positions to determine the particle position and depth.…”

“…the generation of image artifacts known as ghost particles), limited particle number density, complexity of the experimental arrangement, and the expense of the overall system. Synthetic aperture PIV (SAPIV) is the most recent advance in 3-D PIV techniques, described by Belden et al 9 The technique uses a large camera array (eight or more cameras) to capture multiple views of the measurement volume simultaneously. In contrast to Tomo-PIV, the map-shift-average algorithm is used to construct synthetically refocused images from the individual views by projecting each view onto a common focal surface.…”