Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session G14: Experimental Techniques IV: PIV - Uncertainty/Microscopic |
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Chair: Pavlos Vlachos, Virginia Polytechnic Institute and State University Room: 302 |
Monday, November 25, 2013 8:00AM - 8:13AM |
G14.00001: Uncertainty estimation for Stereo-Particle Image Velocimetry measurements Sayantan Bhattacharya, Brett Meyers, Matthew Giarra, Roderick La Foy, Pavlos Vlacjos Stereographic Particle Image Velocimetry (SPIV) is a standard method of estimating three-component fluid velocity fields from a two-dimensional field of view using two viewing angles. SPIV techniques involve a series of procedures such as camera calibration, image de-warping, velocity field reconstruction, etc., and the contribution of each step to the overall uncertainty of the measurement is not well understood. Previous efforts have been made to quantify errors involved at each stage of the 3D velocity reconstruction, but have fallen short of a rigorous analysis of the combination of errors for a range of parameters. Such analysis is performed herein. In the present work the Type A uncertainty is evaluated for each step of an SPIV method (involving self calibration and both 3D calibration-based reconstruction and geometric reconstruction) for a set of simulated images. A simulated vortex ring image set was used as a test case and the particle seeding density, light sheet thickness, image magnification, and viewing angles were varied parametrically. Propagation of systematic and random standard uncertainty using both Taylor series and Monte-Carlo method was performed. The results are also compared with prior 2D PIV uncertainty analysis. [Preview Abstract] |
Monday, November 25, 2013 8:13AM - 8:26AM |
G14.00002: Evaluation of multi-pulse PIV for spatial resolution, velocity accuracy and acceleration measurement Liuyang Ding, Ronald Adrian, Sivaram Gogineni, Kathy Prestridge The performance of multi-pulse PIV is numerically evaluated based on PTV simulation. We compare triple-pulse and quadruple-pulse to conventional double-pulse PIV regarding their performance on spatial resolution, velocity and acceleration measurement. The optimization is achieved to minimize the combined error in position, velocity and acceleration. Multi-pulse technology is then tested by measuring simultaneous velocity and acceleration fields of a round impinging air jet. Experimental results from triple-pulse and quadruple-pulse are compared and discussed in terms of the accuracy and performance. [Preview Abstract] |
Monday, November 25, 2013 8:26AM - 8:39AM |
G14.00003: 3 Component PIV Uncertainty Scott Warner, Barton Smith The random uncertainty of 2-component (2C) Particle Image Velocimetry (PIV) has recently been addressed in three unique methods called the Uncertainty Surface Method (USM) from Utah State University, Image Matching (IM) method from Lavision and Delft, and correlation Signal to Noise Ration (SNR) methods from Virginia Tech. Since 3C (stereo) Particle Image Velocimetry (PIV) velocity fields are derived from two, 2C fields, random uncertainties from the 2C fields clearly propagate into the 3C field. In this work, we will demonstrate such a propagation using commercial PIV software and the USM method, although the propagation works similarly for any 2C random uncertainty method. Stereo calibration information is needed to perform this propagation. As a starting point, a pair of 2C uncertainty fields will be combined in exactly the same manner as velocity fields to form a 3C uncertainty field using commercial software. Correlated uncertainties between the components in the two 2C fields will be addressed. These results will then by compared to a more rigorous propagation, which requires access to the calibration information. [Preview Abstract] |
Monday, November 25, 2013 8:39AM - 8:52AM |
G14.00004: Effects of Spatial Alignment in Stereo Particle Image Velocimetry Barton Smith, Steven Beresh We seek to quantity errors in stereo Particle Image Velocimetry (PIV) as a function of laser sheet thickness and camera angle. Simultaneous stereo PIV measurements of a simple free jet were obtained from narrow and wide camera angles while a fifth camera viewed the laser sheet from 90 degrees to determine the two-component velocity field free of errors resulting from stereo calibration. Errors in mean velocities were small, but artificially reduced turbulent stresses were generated when self-calibration was not used, owing to a smearing effect that occurs when the two cameras are inadequately registered to each other. This difficulty worsens with increased laser sheet thickness. Spatial error in the calibration process can artificially displace vector fields from the expected origin. Although this typically is small with respect to statistical properties of a data set, it can be prominent when instantaneous snapshots of the velocity field are examined, particularly where the velocity gradient is momentarily large. Furthermore, small scale structures present in the jet flow are distorted by the various PIV systems in a manner that depends on the sheet thickness and camera orientation. [Preview Abstract] |
Monday, November 25, 2013 8:52AM - 9:05AM |
G14.00005: Correlation plane statistical analysis for estimation of measurement uncertainty for Particle Image Velocimetry Zhenyu Xue, John Charonko, Pavlos Vlachos Early development of Particle Image Velocimetry (PIV) methods did not involve quantification of measurement uncertainty, which in result created skepticism about the reliability of PIV. Quantification of PIV uncertainty is complex because coupled sources are involved in PIV measurement. Recently several attempts have been proposed. However, most of those methods were ``posteriori'' methods: deducing the uncertainty from post-processing of recorded images, or using observed relationships between metrics calculated from images, flow field and the resulting error distribution. Here we propose a novel theoretical and statistical PIV uncertainty estimation approach. It is based on the notion that the correlation plane represents the probability distribution function (PDF) of all possible particle displacements convoluted with particle shape information. The PDF can be obtained by de-convolving the particle information from original correlation plane. Knowing the primary peak of correlation plane indicates the most probable displacement, and the PDF, standard deviation of measured displacement, i.e. the uncertainty, can be calculated by computing the second order moment about the most probable displacement. We will present theoretical and statistical foundations of this method, we will validate each performance with synthetic image sets, and finally we will show its application on real experiment data. [Preview Abstract] |
Monday, November 25, 2013 9:05AM - 9:18AM |
G14.00006: Nano-scale velocimetry with Bessel Beam Microscopy Craig Snoeyink Bessel Beam Microscopy is a unique imaging technique that places an axicon in the imaging path of a microscope. Here we will discuss recent advances in this technique including single-acquisition with 40\% improved spatial resolution and single-view three-dimensional particle tracking with greatly enhanced depth resolution. These capabilities lead to enhanced resolution in velocimetry techniques. For example, when using BBM to perform Particle Image Velocimetry (PIV) the increased image spatial resolution allows for a corresponding increase in velocity field spatial resolution. The greatly increased depth resolution, on the order of 100 nm with a 10x objective, can greatly increase the spatial resolution of Particle Tracking Velocimetry (PTV) measurements. [Preview Abstract] |
Monday, November 25, 2013 9:18AM - 9:31AM |
G14.00007: Development of real time digital holographic microscope for cell flow interactions using a High Performance Computing (HPC) cluster Avesta Hojjati, Mehdi Molaei, Jian Sheng Real-time imaging and analysis of 3D cell migration and locomotion is crucial to understand the underlying physics of cell environment interactions. In addition, such a microscopy would provide vital diagnostic capability in cell detection, particle sorting and drug screening with large throughput. However, 3D holographic imaging and subsequent analysis are computational intensive and up-to-date prohibitive for real-time applications. With the advances in high performance computing, we are developing a real-time digital holographic microscope (DHM) that includes an in-line DHM, a large format CCD camera, and a 24-node windows-based HPC cluster. The cluster is organized as the master-slave parallel computing paradigm with Message Passing Interface (MPI) as its communication protocol. The holograms are recorded, streamed and analyzed by the HPC cluster in real time, the 3D distributions and in focus images are rendered back on the data acquisition computer. The system will be applied to study marine protest interacting with oil droplets. Supports from GoMRI are acknowledged. [Preview Abstract] |
Monday, November 25, 2013 9:31AM - 9:44AM |
G14.00008: Real and virtual image separation in digital in-line holography microscopy by recording two parallel holograms Hangjian Ling, Joseph Katz Maintaining high magnification and micron resolution in applications of digital in-line holography microscopy for 3D velocity measurements requires a hologram plane located very close or even within the sample volume. Separation between overlapping real and virtual images becomes a challenge in such cases. Here, we introduced a simple method based on recording two holograms through the same microscope objective that are separated by a short distance from each other. When the same particle fields are reconstructed from the two holograms, the real images overlap, whereas virtual images are separated by twice the distance between hologram planes. Thus, real and virtual images can be easily distinguished. Due to the elongation of the reconstructed particle in the axial direction, the distance between hologram planes is selected to exceed the elongated traces. This technique has been applied to record 3D traces of thousands of 2 um particles in a $0.5\times 0.5\times 0.5$ mm sample volume using hologram planes separated by 27 um. Experimental setup, alignment and data analysis procedures, including reconstruction, calibration, particles segmentation and precision particles positioning will be discussed. [Preview Abstract] |
Monday, November 25, 2013 9:44AM - 9:57AM |
G14.00009: Turbulent Boundary Layer Facility to Investigate Superhydrophobic Drag Reduction James W. Gose, Marc Perlin, Steven L. Ceccio Recent developments in superhydrophobic surfaces have led to potential economic and environmental benefits, perhaps most notably in skin-friction drag reduction. A team from the University of Michigan has developed a recirculating turbulent boundary layer facility to investigate the reduction of drag along engineered superhydrophobic surfaces (SHS). The facility can accommodate both small and large SHS samples in a test section 7 mm (depth) x 100 mm (span) x 1000 mm (length). Coupled with an 11.2 kilowatt pump and a 30:1 contraction the facility is capable of producing an average flow velocity of 25 m/s, yielding a Reynolds number of 84,000. Flexure-mounted test samples subjected to shear deflect to a max of 50 microns; movements are measured using a digital microscope composed of a high-resolution camera and a water immersion objective. The setup yields an optical resolution of about one micron whereas sub-micron resolution is achieved by implementing an FFT of two Ronchi rulings. Additional drag measurement methods include pressure drop across the test specimen and PIV measured boundary layers. Additional SHS investigations include the implementation of active gas replenishment, providing an opportunity to replace gas-pockets that would otherwise be disrupted in traditional passive SHS surfaces due to high shear stress and turbulent pressure fluctuations. [Preview Abstract] |
Monday, November 25, 2013 9:57AM - 10:10AM |
G14.00010: Echo Particle Image Velocimetry Measurements of Liquified Biomass Nicholas DeMarchi, Christopher White Echo particle image velocimetry (EPIV) is used to acquire planar fields of velocity in pipe flow of liquefied biomass. The biomass studied is pre-treated (i.e., acid washed) corn stover and it is liquefied by enzymatic hydrolysis. The liquefaction process is carried out for various biomass mass loadings (1.5\%-15\%). For each biomass loading, the fluid's microstructure and rheology are studied and EPIV measurements are acquired. The aim is to demonstrate the usefulness of EPIV to acquire planar fields of velocity in optically opaque flows and to evaluate the effect of particle size, distribution, and mass loading of the dispersed solid phase on the EPIV measurements. [Preview Abstract] |
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