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Abstract Optical flow methods have been developed over the past two decades for application to PIV images with the goal of acquiring higher resolution measurements of the velocity field than conventional cross-correlation-based techniques. Numerous optical flow velocimetry (OFV) algorithms have been devised to solve the ill-posed optical flow problem, with various physics-inspired strategies to tailor them to fluid flows. While OFV can be applied to continuous scalar fields, it has demonstrated the most success on images of tracer particles, i.e.\ traditional planar PIV images. Compared to state-of-the-art cross-correlation algorithms, OFV methods have demonstrated an order of magnitude increase in spatial resolution and up to a factor of two improvement in overall accuracy when evaluated on synthetic data, at the cost of increased computational time. The requirements for particle seeding density, inter-frame displacement, and image quality are also more stringent for OFV methods compared to cross-correlation. OFV has been applied sparingly in experiments to date, but appears to offer the same advantages demonstrated on synthetic data. At this stage, OFV seems best suited to planar velocity measurements, although extensions to stereoscopic measurements have been demonstrated.
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Regularized tomographic PIV for incompressible flows based on conservation of mass
Three-dimensional and three-component (3D3C) velocity measurements have long been desired to resolve the 3D spatial structures of turbulent flows. Recent advancements have demonstrated tomographic particle image velocimetry (tomo-PIV) as a powerful technique to enable such measurements. The existing tomo-PIV technique obtains 3D3C velocity field by cross-correlating two frames of 3D tomographic reconstructions of the seeding particles. A most important issue in 3D3C velocity measurement involves uncertainty, as the derivatives of the measurements are usually of ultimate interest and uncertainties are amplified when calculating derivatives. To reduce the uncertainties of 3D3C velocity measurements, this work developed a regularized tomo-PIV method. The new method was demonstrated to enhance accuracy significantly by incorporating the conservation of mass into the tomo-PIV process. The new method was demonstrated and validated both experimentally and numerically. The results illustrated that the new method was able to enhance the accuracy of 3D3C velocity measurements by 40%–50% in terms of velocity magnitude and by 0.6°–1.1° in terms of velocity orientation, compared to the existing tomo-PIV technique. These improvements brought about by the new method are expected to expand the application of tomo-PIV techniques when accuracy and quantitative 3D flow properties are required.
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- Award ID(s):
- 1839603
- PAR ID:
- 10134345
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Applied Optics
- Volume:
- 59
- Issue:
- 6
- ISSN:
- 1559-128X; APOPAI
- Format(s):
- Medium: X Size: Article No. 1667
- Size(s):
- Article No. 1667
- Sponsoring Org:
- National Science Foundation
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