Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session L29: Experimental Techniques: PIV I 
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Chair: John Charonko, Los Alamos National Laboratory Room: 2014 
Monday, November 24, 2014 3:35PM  3:48PM 
L29.00001: Triple Pulse Particle Image Velocimeter/Accelerometer Measurements of FlowStructure Interaction Sivaram Gogineni, Liuyang Ding, Ronald Adrian A PIVbased instrument has been developed to measure position, velocity and acceleration of moving in fluids and the velocity and acceleration fields of the fluid motion simultaneously. The instrument extends conventional PIV by adding a third and sometimes fourth pulse, thereby increasing spatial resolution, velocity accuracy and enabling acceleration measurement. Images of the moving solid body are segmented from the fluid field and displacements are measured by crosscorrelation, as in the fluid. To test the capabilities of this approach, a cylinder supported by elastic rods is oscillated sinusoidally in water to produce shed vortices that interact with the cylinder nonlinearly Phase averaged fields are obtained in the fluid, and accuracy of the measurements is assessed by comparing the measurements of fluid velocity and acceleration to solid their known counterparts at the solidfluid interface, [Preview Abstract] 
Monday, November 24, 2014 3:48PM  4:01PM 
L29.00002: Optimization and Application of Surface Segmentation Technique for Tomographic PIV Liuyang Ding, Ronald Adrian, Brandon Wilson, Kathy Prestridge Tomographic PIV is a widely used 3D flow measurement technique. It utilizes images recorded by multiple cameras to reconstruct the intensity distribution of a measured volume. The 3D3C velocity field is then computed by 3D crosscorrelation. Surface segmentation [1] aims to reduce computational cost. It extracts from a cloud of particles an image of those particles that lie on a mathematically prescribed surface. 2D2C velocity fields are computed on stacks of orthogonal surfaces, then assembled to construct the full 3D3C velocity field. We investigate the reconstruction of adaptive surfaces aligned with the main flow direction minimizing the outofplane motion. Numerical assessment is performed on curvedsurface reconstruction for TaylorCouette flow. An optimizing 2D interrogation scheme involving volumetric deformation is proposed to improve the accuracy of the 3D3C velocity field. The numerical test is performed on a synthetic vortex ring showing good measurement accuracy. Experimental results measuring the shockdriven turbulent mixing will also be presented. References [1] Ziskin, I.B., R.J. Adrian, and K. Prestridge. ``Volume segmentation tomographic particle image velocimetry.'' Proceedings of 9th international symposium on particle image velocimetry, Kobe, Japan. 2011. [Preview Abstract] 
Monday, November 24, 2014 4:01PM  4:14PM 
L29.00003: A Green's function approach to PIV Pressure estimates Oleg Goushcha, Peter Ganatos, Niell Elvin, Yiannis Andreopoulos Spatial resolution of PIV data limits the ability to calculate the pressure along a solid boundary of a body immersed in a fluid and hence to accurately estimate the force exerted. Current methodologies solve numerically NavierStokes equations to calculate the pressure field from velocity data. An analytical approach has the potential of more accurate estimation of pressure in comparison to existing methods. A methodology has been developed to calculate the pressure distribution on the body in the flow by analytically solving the pressure Poisson Equation using a Green's function approach. The pressure is then extrapolated to the solid boundary resulting in an accurate pressure distribution and total net force on the boundary. This technique has been applied to the case of a flexible cantilever beam vibrating after interacting with a traveling vortex in an experimental setup to harvest energy from an airflow. Timeresolved PIV has been used to acquire a twodimensional velocity field which has been used to obtain a timedependent pressure distribution acting on the surface of the beam and resultant forces. The analytical solution is compared to the force measured directly by a force sensor placed at the base of the beam as well as the power harvested. [Preview Abstract] 
Monday, November 24, 2014 4:14PM  4:27PM 
L29.00004: Effects of 3D PIV postprocessing on impulse and force analysis in vortical flows Leah Mendelson, Alexandra Techet Vortical flows measured using 3D PIV techniques are fundamentally filtered versions of physical phenomena, with velocity information lost below the length and time scales of the measurement system. In the context of propulsive vortices, such as those generated during biological locomotion, these factors, combined with experimental noise and error, can lead to inaccuracies in analysis of the vortex momentum and net thrust. As a result, while 3D velocity measurements remove many of the assumptions required to analyze planar PIV data, they should not be considered absolute physical quantities. Our work focuses on postprocessing for 3D PIV data sets to enable the extraction of accurate, quantitative 3D force measurements for unsteady vortical propulsion. In this study, we compare utilizing measurement signal processing techniques, orthogonal decomposition, and identification of coherent structures to measure the impulse of a canonical vortex ring generated by a mechanical piston. In particular, we consider the ability of these methods to confront the influences of limited spatial resolution and arbitrary geometries, and make recommendations for a general procedure for propulsion analysis from 3D PIV data, regardless of which PIV technique is used to obtain the velocity fields. [Preview Abstract] 
Monday, November 24, 2014 4:27PM  4:40PM 
L29.00005: Method for fast and non iterative synthetic aperture reconstruction for 3D PIV and PTV Abhishek Bajpayee, Alexandra Techet Three dimensional particle image velocimetry (PIV) is becoming a widely used measurement technique since the introduction of tomographic PIV by Elsinga et al. (2006). New methods such as synthetic aperture PIV have recently been demonstrated as a viable alternative to tomographic PIV, and extended for accurate 3D particle tracking velocimetry (PTV) by Bajpayee et al. in 2013. Presented here is an improvement to the synthetic aperture reconstruction technique, using a homography fit (HF) method for projecting points into a camera through refractive interfaces, that allows non iterative, accurate and significantly faster reconstruction. The underlying algorithm is computationally cheap and can be easily and massively parallelized thereby allowing further improvement in speed depending on the hardware available. [Preview Abstract] 
Monday, November 24, 2014 4:40PM  4:53PM 
L29.00006: Application of Plenoptic PIV for 3D Velocity Measurements Over Roughness Elements in a Refractive Index Matched Facility Brian Thurow, Kyle Johnson, Taehoon Kim, Gianluca Blois, Jim Best, Ken Christensen The application of Plenoptic PIV in a Refractive Index Matched (RIM) facility housed at Illinois is presented. Plenoptic PIV is an emerging 3D diagnostic that exploits the lightfield imaging capabilities of a plenoptic camera. Plenoptic cameras utilize a microlens array to measure the position and angle of light rays captured by the camera. 3D/3C velocity fields are determined through application of the MART algorithm for volume reconstruction and a conventional 3D crosscorrelation PIV algorithm. The RIM facility is a recirculating tunnel with a 62.5{\%} aqueous solution of sodium iodide used as the working fluid. Its resulting index of 1.49 is equal to that of acrylic. Plenoptic PIV was used to measure the 3D velocity field of a turbulent boundary layer flow over a smooth wall, a single wallmounted hemisphere and a full array of hemispheres (i.e. a rough wall) with a k/$\delta \quad \approx $ 4.6. Preliminary time averaged and instantaneous 3D velocity fields will be presented. [Preview Abstract] 

L29.00007: ABSTRACT WITHDRAWN 
Monday, November 24, 2014 5:06PM  5:19PM 
L29.00008: New experimental opportunities using refraction matched hydrogel: invisible objects, arrays, and features that obstruct flow but not light Joel Weitzman, Lianna Samuel, Anna Craig, Robert Zeller, Stephen Monismith, Jeffrey Koseff Water flow in and around immersed bodies, roughness arrays, and major bathymetric features is characterized by a large amount of spatial complexity. In both natural and designed settings, the associated hydrodynamic intricacies have influence on energy dissipation, thermal transfer, and mass exchange. However, the same surfaces that disrupt and redirect fluid motion also greatly restrict observation and measurement options. Solid boundaries tend to limit instrument access and block optical lines of sight. This presentation introduces a new technique expressly designed to overcome these hurdles. Highcomplexity solid models have been manufactured using a unique superabsorbent copolymer hydrogel. This material is wholly transparent, with an index of refraction nearly identical to that of water. When hydrogel object are submerged, light passes through them just as it passes through the fluid itself. Consequently, these objects and all their features become indistinguishable from their surroundings  effectively invisible. This opens up the entire internal flow field to direct observation and highresolution quantitative measurement, a feat accomplished without reliance on unconventional fluids or specialized flow facilities. [Preview Abstract] 
Monday, November 24, 2014 5:19PM  5:32PM 
L29.00009: On the Application of Compressed Sensing to NonTimeResolved PIV Measurements Eric Deem, Timothy Davis, Louis Cattafesta, Farrukh Alvi Temporally resolved, fullfield flow measurements are still impractical for most flows of interest. Fortunately, the spectral content of many flows can be described in a low dimensional space. This sparsity has inspired the recent adaptation of compressed sensing into the fluid mechanics community as a method for reconstructing spectral content of subNyquist sampled data (arXiv:1401.7047). We apply this method to the analysis of several example fluid flow data sets, varying in spectral content. These data sets include the measured flow about a highlift airfoil, an impinging jet, and a zeronet massflux (ZNMF) actuator. The Proper Orthogonal Decomposition (POD) is applied to the random PIV snapshots and we apply Orthogonal Matching Pursuit (OMP) to approximate the discrete Fourier transform of the POD coefficients. Additionally, reconstruction parameters are varied for to examine criteria regarding the probability of a successful reconstruction versus the degree of spectral sparsity. The advantages and restrictions of this method are discussed. [Preview Abstract] 
Monday, November 24, 2014 5:32PM  5:45PM 
L29.00010: Wave and flow field phenomena in planar falling films by simultaneous LaserInduced Fluorescence and Particle Image/Tracking Velocimetry Alexandros Charogiannis, Ivan Zadrazil, Christos Markides Falling films along an inclined flat plane test section were investigated using simultaneous LaserInduced Fluorescence and Particle Image/Tracking Velocimetry techniques. The investigated conditions covered a range of Reynolds (2.2  8.2) and Kapitza numbers (28.6  41.4). The main challenge of the research is the development of routines that allow for simultaneous detailed measurements of liquid film topology as well as the instantaneous velocity fields within the liquid film while correcting for the refractive index discrepancy at the solidliquid and gasliquid interfaces. The uncertainties of the laserbased measurement techniques used to determine the local film thickness were compared with a micrometer based measurements as well as with the solution to the NavierStokes equations based on the assumptions for 1D steady and fully developed flow. The results presented consist of indetail characterisation of the aforementioned conditions as well as of flows with inlet pulsation frequencies in the range 1  8 Hz. [Preview Abstract] 
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