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Abstract High fidelity near-wall velocity measurements in wall bounded fluid flows continue to pose a challenge and the resulting limitations on available experimental data cloud our understanding of the near-wall velocity behavior in turbulent boundary layers. One of the challenges is the spatial averaging and limited spatial resolution inherent to cross-correlation-based particle image velocimetry (PIV) methods. To circumvent this difficulty, we implement an explicit no-slip boundary condition in a wavelet-based optical flow velocimetry (wOFV) method. It is found that the no-slip boundary condition on the velocity field can be implemented in wOFV by transforming the constraint to the wavelet domain through a series of algebraic linear transformations, which are formulated in terms of the known wavelet filter matrices, and then satisfying the resulting constraint on the wavelet coefficients using constrained optimization for the optical flow functional minimization. The developed method is then used to study the classical problem of a turbulent channel flow using synthetic data from a direct numerical simulation (DNS) and experimental particle image data from a zero pressure gradient, high Reynolds number turbulent boundary layer. The results obtained by successfully implementing the no-slip boundary condition are compared to velocity measurements from wOFV without the no-slip condition and to a commercial PIV code, using the velocity from the DNS as ground truth. It is found that wOFV with the no-slip condition successfully resolves the near-wall profile with enhanced accuracy compared to the other velocimetry methods, as well as other derived quantities such as wall shear and turbulent intensity, without sacrificing accuracy away from the wall, leading to state of the art measurements in the region of the turbulent boundary layer when applied to experimental particle images.
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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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