Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session D16: Experimental Techniques II |
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Chair: Pavlos Vlachos, Virginia Polytechnic Institute and State University Room: 319 |
Sunday, November 20, 2011 2:10PM - 2:23PM |
D16.00001: Tomographic particle image velocimetry over a triangular prism in unidirectional flows In Mei Sou, Joseph Calantoni Using tomographic particle image velocimetry (Tomo-PIV), the full three-dimensional-three-component (3D-3C) flow structure and turbulence characteristics over a triangular prism in a recirculating water tunnel were investigated. Here we present preliminary results from a new Tomo-PIV system for subcritical Froude number flows. Large-scale vortex shedding from the tip of the triangular prism is observed. Results of coherent structure organization analyzed by 3D vorticity calculation will be presented. Using the full 3D-3C instantaneous velocity field, turbulent kinetic energy is directly evaluated without any of the assumptions often needed for 2D PIV measurements. Details of the experimental setup including a unique device designed to perform our Tomo-PIV volume calibration will be discussed. We perform an in-depth turbulent kinetic energy budget and explore the feasibility of extending the measurement technique to other complex flows. [Preview Abstract] |
Sunday, November 20, 2011 2:23PM - 2:36PM |
D16.00002: Simultaneous 3D Strain and Flow Fields Measurement of a Model Artery under Unsteady Flows Mostafa Toloui, Jian Sheng Fluid-Structure Interaction imposes challenges in both aero-elasticity and biomedical studies. A simultaneous solid deformation and fluid flow measurement technique based on digital in-line holographic particle tracking velocimetry (PTV) has been developed. It allows us to measure concurrently 3D strain field of a deforming structure and the unsteady flow near it. To facilitate the measurement, both wall and flow are seeded with tracer particles distinguished by size. The motion of these tracers provides the 3D deformation of the wall and the 3D velocity distribution of the flow separately. A fully index matched facility including transparent artery and NaI solution is constructed to enable observations near the wall or through the complex geometry. An arterial model with the inner diameter of 9.5 mm and the thickness of 0.9 mm is manufactured from the cross-linked transparent PDMS at the mixing ratio of 1:10 and doped with mono-dispersed 19 $\mu $m polystyrene particles. A cinematic holographic PTV system is used to trace the 3D particle motion in the model and flow simultaneously. Preliminary study is performed within a sample volume of 15 $\times $ 15 $\times $ 75 mm with the spatial resolution of 7.4 $\mu $m in lateral and 10 $\mu $m in depth. Uncertainty and accuracy analysis will be reported. [Preview Abstract] |
Sunday, November 20, 2011 2:36PM - 2:49PM |
D16.00003: Simultaneous 3D measurement of flow velocities and an arbitrarily moving surface Young Jin Jeon, Hyung Jin Sung Simultaneous 3D measurement technique for flow velocities and an arbitrarily moving surface has been developed by applying image processing methods to the tomographic PIV. Particles and a surface were captured simultaneously through a conventional PIV system without additional cameras or an illumination device. To adjust the optimal exposure times of particles and the surface in the similar time scales, red fluorescent tracer particles were used and long pass glass filters were installed in the lens system. The volume self calibration was employed for improving the 3D reconstruction qualities. Particles and a surface image could be separated by using an image separation. 3D surface shapes were then reconstructed by applying the feature detection and the morphological evaluation to the surface image. Subsequently, particle volumes were reconstructed by MLOS-SMART. The surface reconstruction procedure was validated for various known shaped bodies. Experiments for flows around a rotating cylinder, a flag motion and a flapping flag were carried out to investigate the applicability of the present technique. [Preview Abstract] |
Sunday, November 20, 2011 2:49PM - 3:02PM |
D16.00004: Visual hull method for tomographic PIV of flow around moving objects Deepak Adhikari, Ellen Longmire Measurement of velocity around arbitrarily moving objects is of interest in many applications. This includes flow around marine animals and flying insects, flow around supercavitating projectiles, and flow around discrete drops or particles in multiphase flows. We present a visual hull technique that employs existing tomographic PIV reconstruction software to automate identification, masking and tracking of discrete objects within a three-dimensional volume, while allowing computation and avoiding contamination of the surrounding three-component fluid velocity vectors. The technique is demonstrated by considering flow around falling objects of different shape, namely a sphere, cube, tetrahedron and cylinder. Four high-speed cameras and a laser are used to acquire images of these objects falling within liquid seeded with tracer particles. The acquired image sets are then processed to reconstruct both the object and the surrounding tracer particles. The reconstructed object is used to estimate the object location at each time step and mask the reconstructed particle volume, while the reconstructed tracer particles are cross-correlated with subsequent particle volumes to obtain the fluid velocity vectors. [Preview Abstract] |
Sunday, November 20, 2011 3:02PM - 3:15PM |
D16.00005: Recent advancements in tracer particle based-interface reconstruction Massimiliano Rossi, Christian Cierpka, Rodrigo Segura, Christian J. K\"ahler Tracer particles are commonly used in experimental fluid dynamics to probe the velocity of a flow. An example are particle tracking velocimetry methods (PTV), in which the velocity field is obtained by tracking the position of individual tracer particles in a control volume at different time instants. It has been recently demonstrated how this approach can be extended to successfully reconstruct the interface between two fluid phases. This procedure has some advantages compared to traditional methods using dye visualization, since the diffusion coefficient of tracer particles is considerably smaller than the one of molecular dyes and the 3D topology of an interface can be obtained from a single recording (using 3D-PTV), with no need of scanning procedures. The main limitation of this approach is clearly due to the resolution of the reconstruction that is constrained to the tracer particle density. In this work, the latest developments of this method are presented, in particular showing the possibility to perform 3D-time-resolved measurements. Results on the shape of droplets and free-surface waves are provided. [Preview Abstract] |
Sunday, November 20, 2011 3:15PM - 3:28PM |
D16.00006: Volume Segmentation and Ghost Particles Isaac Ziskin, Ronald Adrian Volume Segmentation Tomographic PIV (VS-TPIV) is a type of tomographic PIV in which images of particles in a relatively thick volume are segmented into images on a set of much thinner volumes that may be approximated as planes, as in 2D planar PIV. The planes of images can be analysed by standard mono-PIV, and the volume of flow vectors can be recreated by assembling the planes of vectors. The interrogation process is similar to a Holographic PIV analysis, except that the planes of image data are extracted from two-dimensional camera images of the volume of particles instead of three-dimensional holographic images. Like the tomographic PIV method using the MART algorithm, Volume Segmentation requires at least two cameras and works best with three or four. Unlike the MART method, Volume Segmentation does not require reconstruction of individual particle images one pixel at a time and it does not require an iterative process, so it operates much faster. As in all tomographic reconstruction strategies, ambiguities known as ghost particles are produced in the segmentation process. The effect of these ghost particles on the PIV measurement is discussed. [Preview Abstract] |
Sunday, November 20, 2011 3:28PM - 3:41PM |
D16.00007: Iterative Reconstruction of Volumetric Particle Distribution for 3D Velocimetry Bernhard Wieneke, Douglas Neal A number of different volumetric flow measurement techniques exist for following the motion of illuminated particles. For experiments that have lower seeding densities, 3D-PTV uses recorded images from typically 3-4 cameras and then tracks the individual particles in space and time. This technique is effective in flows that have lower seeding densities. For flows that have a higher seeding density, tomographic PIV uses a tomographic reconstruction algorithm (e.g. MART) to reconstruct voxel intensities of the recorded volume followed by the cross-correlation of subvolumes to provide the instantaneous 3D vector fields on a regular grid. A new hybrid algorithm is presented which iteratively reconstructs the 3D-particle distribution directly using particles with certain imaging properties instead of voxels as base functions. It is shown with synthetic data that this method is capable of reconstructing densely seeded flows up to 0.05 particles per pixel (ppp) with the same or higher accuracy than 3D-PTV and tomographic PIV. Finally, this new method is validated using experimental data on a turbulent jet. [Preview Abstract] |
Sunday, November 20, 2011 3:41PM - 3:54PM |
D16.00008: Analysis of an Optimized MLOS Tomographic Reconstruction Algorithm and Comparison to the MART Reconstruction Algorithm Roderick La Foy, Pavlos Vlachos An optimally designed MLOS tomographic reconstruction algorithm for use in 3D PIV and PTV applications is analyzed. Using a set of optimized reconstruction parameters, the reconstructions produced by the MLOS algorithm are shown to be comparable to reconstructions produced by the MART algorithm for a range of camera geometries, camera numbers, and particle seeding densities. The resultant velocity field error calculated using PIV and PTV algorithms is further minimized by applying both pre and post processing to the reconstructed data sets. [Preview Abstract] |
Sunday, November 20, 2011 3:54PM - 4:07PM |
D16.00009: Quantitative visualization of fine-scale three-dimensional flow structures in turbulence using time-resolved stereoscopic scanning Particle Image Velocimetry Ye Cheng, Francisco Javier Diez A time-resolved stereoscopic scanning particle image velocimetry (TR-SSPIV) system is developed to investigate the fine-scale 3D structures in free shear turbulent jets. The system provides a simultaneous measurement of the three-component velocity field in a three-dimensional volume (3D3C) with Kolmogorov-scale ($\eta )$ resolution, offering a true representation of the complete nine-component velocity gradient tensor. Quantitative visualization of the coherent structures at fine-scale turbulence is obtained and four basic structural shapes (sheets, tube, square ribbons and spherical blobs) are identified as building blocks of complex turbulent structures. The local acceleration ${\partial {\rm {\bf u}}} \mathord{\left/ {\vphantom {{\partial {\rm {\bf u}}} {\partial t}}} \right. \kern-\nulldelimiterspace} {\partial t}$ is obtained and represented as 3D structures, which showed a strong anti-alignment with the convective acceleration terms. A novel vortex identification scheme is introduced based on the local pressure. This method gives more direct description of vortex cores, compared to previously published ones including enstrophy, Q, $\lambda _2 $ and $\Delta $ criteria. Extensive statistical analyses are performed to study the probability density function (PDF), joint PDF, and spectra of the velocity gradients, enstrophy production rate and energy dissipation rate to compare with isotropy theory. [Preview Abstract] |
Sunday, November 20, 2011 4:07PM - 4:20PM |
D16.00010: Three-dimensional measurement of the laminar flow field inside a static mixer Michel Speetjens, Rene Jilisen, Paul Bloemen Static mixers are widely used in industry for laminar mixing of viscous fluids as e.g. polymers and food stuffs. Moreover, given the similarities in flow regime, static mixers often serve as model for compact mixers for process intensification and even for micro-mixers. This practical relevance has motivated a host of studies on the mixing characteristics of static mixers and their small-scale counterparts. However, these studies are primarily theoretical and numerical. Experimental studies, in contrast, are relatively rare and typically restricted to local 2D flow characteristics or integral quantities (pressure drop, residence-time distributions). The current study concerns 3D measurements on the laminar flow field inside a static mixer using 3D Particle-Tracking Velocimetry (3D-PTV) Key challenges to the 3D-PTV image-processing procedure are the optical distortion and degradation of the particle imagery due to light refraction and reflection caused by the cylindrical boundary and the internal elements. Ways to tackle these challenges are discussed and first successful 3D measurements in an actual industrial static mixer are presented. [Preview Abstract] |
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