Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session LC: Experimental Techniques I |
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Chair: Daniel Troolin, TSI Incorporated Room: Long Beach Convention Center 102A |
Monday, November 22, 2010 3:35PM - 3:48PM |
LC.00001: Stereo PIV Measurements in the Wall-Normal-Spanwise Plane of Turbulent Channel Flow J.M. Barros, K.T. Christensen Stereo PIV measurements are conducted over a $4h\times h$ field of view in the wall-normal--spanwise plane of turbulent channel flow for fully-developed smooth-wall conditions at a friction Reynolds number of 600. These experiments represent a significant challenge to the stereo PIV method as the dominant velocity component is oriented normal to the PIV measurement plane while the in-plane components are much weaker turbulent fluctuations. Validation of the experimental method is achieved via comparison with direct numerical simulation data at a similar Reynolds number. Good agreement is noted both in the mean streamwise velocity as well as the Reynolds normal and shear stresses. Inspection of instantaneous velocity fields in this cross-plane reveals the spatial signatures of low- and high-momentum regions, the former of which have been previously linked to hairpin vortex packets in the outer layer of wall turbulence. These regions can extend to the centerline of the channel and often embody a significant fraction of the Reynolds shear stress. Two-point correlations are used to study the average characteristics of these features on the wall-normal--spanwise plane. [Preview Abstract] |
Monday, November 22, 2010 3:48PM - 4:01PM |
LC.00002: Stereo-PIV study of turbulent flow downstream of a bend in a round pipe Jun Sakakibara, Akira Hashimoto We measured three-components of velocity vector distribution in cross sections of a fully developed turbulent pipe flow downstream of a 90-degree bend by means of stereo PIV. Reynolds number was $Re=120,000$, and ratio of inner diameter $d$ of the pipe and radius of the centerline of the bend was 1.5. Temporal and spatial evolution of turbulent Dean type of vortices has been captured. Proper orthogonal decomposition (POD) was applied to the velocity field in cross-sections. At a streamwise distance $z=2d$ downstream from the bend, the power spectrum of the time-dependent POD coefficient of the 2nd mode shows a dominant peak at $St=0.07$. The power of the 1st and 2nd mode structures identified at $z/d=2 $ were switched further downstream, and the structure of 2nd mode at $z/d=2$ tends to be dominant. Reconstruction of the velocity vector field based on the 1st mode at $z/d=2$ with mean velocity vectors gives flow pattern similar to that of swirl switching, while the 2nd mode at $z/d=2$ is responsible to the rotation of the symmetry plane of the twin vortices. [Preview Abstract] |
Monday, November 22, 2010 4:01PM - 4:14PM |
LC.00003: Simultaneous DDPIV of the elastic wall and working fluid near the reflection sight of a valveless impedance pump John Meier, Derek Rinderknecht, Morteza Gharib Predicting the pressure and flow behavior in microscale impedance pumps is crucial for implementing the pump into microfluidic devices. Studies by Hickerson and Gharib (J. Fluid Mech. 2006) and Avrahami and Gharib (J. Fluid Mech. 2008) highlight the role of wave dynamics, reflections, and resonance in valveless impedance pumps. In this study we investigate the pump performance and motion of the pump wall and working fluid in a 20mm x 10mm x 500$\mu $m planar impedance pump. Elastic membranes impregnated with tracer particles were fabricated in-house with varying mechanical properties. For the first time, using the 3-dimensional DPIV technique known as defocusing digital particle image velocimetry (DDPIV), we were able to simultaneously track the motions of the elastic pump wall and the fluid within the pump. We study the partial pulse reflection at the end of the pump where the elastic membrane is coupled to the rigid flow loop. The behavior of this reflection is critical in determining the performance characteristics of the pump and understanding how to design practical impedance pump devices for microfluidic applications. [Preview Abstract] |
Monday, November 22, 2010 4:14PM - 4:27PM |
LC.00004: PIV measurement of flow around an arbitrarily moving body Young Jin Jeon, Hyung Jin Sung PIV image processing methods for measuring flow velocities around an arbitrarily moving body are proposed. A contour-texture analysis based on user-defined textons is applied to determine the arbitrarily moving interface in the 2D PIV. After the interface tracking procedure is performed, the particle images near the interface are transformed into Cartesian coordinates that are related to the distance from the interface. This transformed image always has a straight interface, so the interrogation windows can easily be arranged at certain distances from the interface. Accurate measurements near the interface can then be achieved by applying the window deformation algorithm in concert with PIV/IG. For a tomographic 3D PIV, a volume reconstruction technique from four views is applied to obtain a three-dimensional shape of the interface. Particle motion analysis is made by the MTE MART algorithm. Quantitative evaluations of this method are performed to computer-generated images and actual PIV measurements. [Preview Abstract] |
Monday, November 22, 2010 4:27PM - 4:40PM |
LC.00005: Scalable Tomographic PIV using a Reprojection Reconstruction Technique Roderick La Foy, Samuel Raben, Pavlos Vlachos Tomographic PIV is becoming a common experimental tool in fluid dynamics, but current algebraic reconstruction algorithms can be prohibitively computationally expensive. To this end, a tomographic reconstruction algorithm was developed that is simple to implement, computationally efficient, and scalable to an arbitrary number of cameras. This method reconstructs volumes from each camera independently by projecting the images back onto the volume using the camera calibration data. The projections from each camera are then combined to form a full three dimensional intensity field. The fluid's velocity field may then be calculated using standard three dimensional PIV or PTV techniques. This algorithm was used to reconstruct intensity fields from both simulated and experimental particle fields. [Preview Abstract] |
Monday, November 22, 2010 4:40PM - 4:53PM |
LC.00006: Reduction in the divergence of Tomographic P.I.V. results, using the method of Projection Onto Convex Sets Thomas Clark, Timothy Nickels Tomographic P.I.V. allows measurement of fully three-dimensional velocity fields within a region of fluid. Experimental error in the measurement process, combined with the differential nature of the divergence operator results in a large error in the divergence of the results. For incompressible flow, a technique is introduced to reduce the divergence of the output results using the method of Projection Onto Convex Sets (POCS). The ``correction'' is formulated using a Lagrangian multiplier and implemented through solution of the Poisson equation in a cuboid domain. In this talk, the formulation of the ``correction'' and the boundary conditions used are presented along with experimental results. Limitations of the technique and possible applications are discussed. [Preview Abstract] |
Monday, November 22, 2010 4:53PM - 5:06PM |
LC.00007: Measurement bias in intensity-based near-surface particle velocimetry due to tracer size variations Wei Wang, Jeffrey Guasto, Peter Huang Near-surface particle-based velocimetry using evanescent wave microscopy has gained popularity for experimental studies in biophysical transport and nanofluidics. This technique is capable of measuring the 3D motion of small fluorescent tracer particles (10 nm to 10 micron) within a few hundred nanometers of a liquid-solid interface. Particle intensity is mapped to distance from the interface using the monotonic decay of the evanescent wave. In this work, we consider the measurement bias introduced by polydisperse tracer particle size on the measured spatial distribution of particles and their implications for nano-scale velocimetry. We present a general model to account for particle size variation and the associated interaction potentials between tracer particles and the solid interface (e.g. electrostatic and van der Waals forces) under typical experimental conditions. [Preview Abstract] |
Monday, November 22, 2010 5:06PM - 5:19PM |
LC.00008: Synchrotron X-Ray Three Dimensional microPIV Elizabeth Voigt, Roderick La Foy, Kamel Fezzaa, Wah Keat Lee, Pavlos Vlachos A study was completed to validate the ability to use x-ray imaging combined with a tomographic algorithm to reconstruct a time resolved three dimensional flow field. In this study an approximately 1 mm cubed region was imaged using a synchrotron x-ray source. The x-ray beam was split in two, projected through the fluid interrogation volume, and focused onto a scintillating crystal. The scintillators were imaged using two high-speed cameras. A variety of flows were tested using 10 micron hollow glass spheres as tracer particles. The images from the cameras were combined using a tomographic algorithm and the velocity fields were calculated using three dimensional PIV and PTV methods. [Preview Abstract] |
Monday, November 22, 2010 5:19PM - 5:32PM |
LC.00009: Development of 3D tomographic X-ray PIV technique Sung Yong Jung, Sang Joon Lee An X-ray tomography particle image velocimetry (PIV) technique employing a medical X-ray tube as a light source was developed to measure three-dimensional velocity field information of various fluid flows. The PIV velocity field measurement technique has been used to extract velocity vectors of tracer particles seeded in a flow by tracing their displacements. The conventional PIV techniques using visible light are inappropriate to measure flows in opaque conduits. To overcome these limitations on special applications, the X-ray PIV technique has been developed. In the X-ray imaging technique, the volumetric information along the pathway of X-ray propagation were compressed on the projected image. Therefore, the X-ray computed tomography has been employed to reconstruct the three-dimensional structure of opaque materials using multiple X-ray images captured at several different angles. As a resent, we could successfully reconstruct a three-dimensional velocity field from two-dimensional image-pair cross-correlation without reconstructing three-dimensional particle images. [Preview Abstract] |
Monday, November 22, 2010 5:32PM - 5:45PM |
LC.00010: Accurate measurement of streamwise vortices in low speed aerodynamic flows Rye M. Waldman, Jun Kudo, Kenneth S. Breuer Low Reynolds number experiments with flapping animals (such as bats and small birds) are of current interest in understanding biological flight mechanics, and due to their application to Micro Air Vehicles (MAVs) which operate in a similar parameter space. Previous PIV wake measurements have described the structures left by bats and birds, and provided insight to the time history of their aerodynamic force generation; however, these studies have faced difficulty drawing quantitative conclusions due to significant experimental challenges associated with the highly three-dimensional and unsteady nature of the flows, and the low wake velocities associated with lifting bodies that only weigh a few grams. This requires the high-speed resolution of small flow features in a large field of view using limited laser energy and finite camera resolution. Cross-stream measurements are further complicated by the high out-of-plane flow which requires thick laser sheets and short interframe times. To quantify and address these challenges we present data from a model study on the wake behind a fixed wing at conditions comparable to those found in biological flight. We present a detailed analysis of the PIV wake measurements, discuss the criteria necessary for accurate measurements, and present a new dual-plane PIV configuration to resolve these issues. [Preview Abstract] |
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