3D Imaging techniques
Several examples below show 3D imaging techniques that we have developed for various applications.
Single camera tomographic particle tracking velocimetry (Peterson, K., Regaard, B., Heinemann, S. and Sick, V., "Single-camera, three-dimensional particle tracking velocimetry," Optics Express 20 (8), 9031–9037 (2012))
This paper introduces single-camera, three-dimensional particle tracking velocimetry (SC3D-PTV), an image-based, single-camera technique for measuring 3-component, volumetric velocity fields in environments with limited optical access, in particular, optically accessible internal combustion engines. The optical components used for SC3D-PTV are similar to those used for two-camera stereoscopic-µPIV, but are adapted to project two simultaneous images onto a single image sensor. A novel PTV algorithm relying on the similarity of the particle images corresponding to a single, physical particle produces 3-component, volumetric velocity fields, rather than the 3-component, planar results obtained with stereoscopic PIV, and without the reconstruction of an instantaneous 3D particle field. The hardware and software used for SC3D-PTV are described, and experimental results are presented.
Volume-resolved flame chemiluminescence and laser-induced fluorescence imaging using plenoptic imaging (Greene, M. and Sick, V., "Volume-resolved flame chemiluminescence and laser-induced fluorescence imaging," Applied Physics B Online First (2013) 10.1007/s00340-013-5664-2)
There is significant need for optical diagnostic techniques to measure instantaneous volumetric vector and scalar distributions in fluid flows and combustion processes. This is especially true for investigations where only limited optical access is available, such as in internal combustion engines, furnaces, flow reactors, etc. While techniques such as tomographic PIV for velocity measurement have emerged and reached a good level of maturity, instantaneous 3D measurements of scalar quantities are not available at the same level. Recently, developments in light field technology have progressed to a degree where implementation into scientific 3D imaging becomes feasible. Others have already demonstrated the utility of light field technology towards imaging high contrast particles for PIV, and for imaging flames when treated as single-surface objects. Here, the applicability and shortcomings of current commercially available light field technology towards volumetric imaging of translucent scalar distributions and flames is investigated. Results are presented from imaging canonical chemiluminescent and laser-induced fluorescent systems. While the current light field technology is able to qualitatively determine the position of surfaces by locating high contrast features, the correlation based reconstruction algorithm is unable to fully reconstruct the imaged objects for quantitative diagnostics. Current analysis algorithms are based on high-contrast correlation schemes, and new tools, possibly based on tomographic concepts, will have to be implemented to reconstruct the full 3D structure of translucent objects for quantitative analysis.
Chen, H. and Sick, V., "Three-Dimensional Three-Component Air Flow Visualization in a Steady-State Engine Flow Bench Using a Plenoptic Camera," SAE Int. J. Engines 10(2):2017, doi:10.4271/2017-01-0614.
Plenoptic particle tracking velocimetry (PTV) shows great potential for three-dimensional, three-component (3D3C) flow measurement with a simple single-camera setup. It is therefore especially promising for applications in systems with limited optical access, such as internal combustion engines. The 3D visualization of a plenoptic imaging system is achieved by inserting a micro-lens array directly anterior to the camera sensor. The depth is calculated from reconstruction of the resulting multi-angle view sub-images. With the present study, we demonstrate the application of a plenoptic system for 3D3C PTV measurement of engine-like air flow in a steady-state engine flow bench. This system consists of a plenoptic camera and a dual-cavity pulsed laser. The accuracy of the plenoptic PTV system was assessed using a dot target moved by a known displacement between two PTV frames. In this manner, the PTV accuracy at different seeding densities, particle displacements for lateral and depth directions, and different depth planes was evaluated. Then, 3D3C PTV was conducted on a steady-state engine flow bench at two different flow conditions; one with strong tumble, the other with a combination of tumble and swirl. Silicone oil droplets were seeded into the air flows and were illuminated by the volume-expanded laser beam. Mie scattering from the droplets was recorded by the plenoptic camera running in double-frame mode. A sequence of double-frame images was required to produce an averaged 3D velocity field. The 3D3C velocity fields for both flow conditions are clearly captured, demonstrating the plenoptic 3D PTV technique as a feasible tool to investigate the complex 3D engine flow.