Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session MN: Experimental Techniques IV: PIV |
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Chair: Ken Kiger, University of Maryland Room: 200C |
Tuesday, November 24, 2009 8:00AM - 8:13AM |
MN.00001: Strategies for PIV Outlier Replacement using Gappy POD Sam Raben, John Charonko, Pavlos Vlachos This work presents methodologies for reconstructing erroneous measurements in gappy DPIV data using Proper Orthogonal Decomposition (POD). Current methods for data reconstruction using POD require a priori knowledge of the true solution [Venturi and Karniadakis, J. Fluid Mech. 2004]. This limitation renders the method ineffective for reconstructing experimental data. Here, strategies for optimizing Gappy POD reconstruction using different criteria for modal convergence as well as an iteratively reducing point selection algorithm are shown. Gappy flow fields were created using wall turbulence DNS data. Gappyness levels of 5\%, 10\%, 20\%, 50\% and, 80\% were created with gap sizes of 1x1, 3x3, 5x5, and arbitrary NxM vector spacing. Noise, equivalent to that of DPIV error, was also added. Data reconstruction accuracy was compared against other currently used methodologies, including bootstrapping, kriging, and the universal outlier detection. The gappy POD method presented here is shown to accurately predict the optimum reconstruction with errors on the order of the error associated with basic DPIV velocity measurements. [Preview Abstract] |
Tuesday, November 24, 2009 8:13AM - 8:26AM |
MN.00002: Quantification of particle concentration in sheet illumination imaging techniques Philip Knowles, Ken Kiger In numerous quantitative imaging methods such as PIV, light sheet illumination is used to limit the region of scattered light close to the focal plane of the camera, effectively improving the contrast of the in-focus image. It is often desirable to use these imaging methods not only to provide displacement information, but also additional metrics such as particle concentration as well. At its simplest level, the quantification of a dispersed particle concentration would seem straightforward: simply count the particles in the image and divide by the interrogation area and light sheet thickness. In practice, however, this typically only yields order-of-magnitude estimates of the concentration. Particle identification within the image will inherently depend on the image size and intensity, which in turn depends on the imaging optics, local illumination and particle position/geometry. In the current work, we demonstrate the influence of the light sheet profile (focusing/attenuation), scattering by tracer particles and wall reflections on determining the effective measurement volume. An empirical calibration method is presented to account for these effects, which allows for quantification of the concentration to within 15\%. Application of this method to a multiphase suspension is demonstrated. This work is supported by the NSF under grant 0351443 and AFOSR grant FA95500810406. [Preview Abstract] |
Tuesday, November 24, 2009 8:26AM - 8:39AM |
MN.00003: ABSTRACT WITHDRAWN |
Tuesday, November 24, 2009 8:39AM - 8:52AM |
MN.00004: Cross-correlation PIV using infrared and visible Nd:YAG pulses and a Nikon dSLR Michael Hallberg, Paul Strykowski A cross-correlation particle image velocimeter is assembled using two Nd:YAG lasers and a Nikon D70 SLR camera. One laser is frequency doubled while the other is not thereby producing a pulse train of two separate colors, green and IR respectively. The internal IR filter is removed from the Nikon D70 and the resulting CCD is sensitive over a range through the visible and into the IR (up to at least 1064nm). Each image was then exposed to both laser pulses revealing two distinct particle images, one green and the other red. The doubly exposed images were separated into two images corresponding to the green channel and the red channel thereby allowing cross-correlation. Initially, the correlation was contaminated by the color filter used to produce the RGB colors on a single CCD, generating a large zero displacement peak. Image processing was employed to reduce the zero peak; the next highest peak generally yielded the particle displacements. Camera manufacturers are developing technologies that will supplant the current color filter (cf. Sigma's image sensor), hopefully making the dSLR a viable option for PIV going forward. [Preview Abstract] |
Tuesday, November 24, 2009 8:52AM - 9:05AM |
MN.00005: In vivo $\mu $PIV measurements of blood velocity in small vessels of a rat model Chia Min Leong, John Russell, Nadine Connor, Markus Honkanen, Timothy Wei Aging-related muscular changes have been shown to affect voice production. There is correlation between muscular changes and changes in capillary hemodynamics and structure with aging. Alterations in oxygen transport to cells and tissues at the capillary level has been hypothesized as one of the key factors that causes muscular changes thus voice production. Since oxygen transport is related to hemodynamics, we start by measuring blood velocity in capillaries of cremaster muscle of a living rat. The $\mu $PIV technique is adapted for measuring blood velocity where red blood cells are used as `seeding particles'. The accuracy of the $\mu $PIV measurements are determined by comparison with results obtained using other techniques such as particle tracking velocimetry (PTV). Finally, challenges in measuring flow through three-dimensional larynx geometry will be discussed. [Preview Abstract] |
Tuesday, November 24, 2009 9:05AM - 9:18AM |
MN.00006: See Through the Static: 3D Synthetic Aperture PIV Jesse Belden, Tadd T. Truscott, Alexandra H. Techet A new method for resolving three-dimensional (3D) fluid velocity fields using a technique called synthetic aperture particle image velocimetry (PIV) is presented. The method makes use of the lightfield imaging and synthetic aperture refocusing techniques that are emerging in the imaging community. Images are captured using an array of cameras positioned on one plane such that the fields of view of the cameras overlap and images can be easily recombined in software using a warp-shift-average algorithm to digitally refocus on different planes. The result is sharply focused particles in the plane of interest, whereas particles out-of-plane appear blurred. The 3D intensity field of particle-laden flows can be reconstructed by refocusing throughout the entire volume and filtering out the blurred particles. 3DPIV techniques can then be applied to these intensity fields to extract velocity data. This technique shows the potential of enabling larger volumes to be resolved with more particles, yielding higher spatial resolution than existing methods. A simulated vortex ring flow field demonstrates the capability of the technique for resolving vector fields in 3D. [Preview Abstract] |
Tuesday, November 24, 2009 9:18AM - 9:31AM |
MN.00007: ABSTRACT WITHDRAWN |
Tuesday, November 24, 2009 9:31AM - 9:44AM |
MN.00008: 3-D Velocity Measurements Around an Optically Suspended Sphere Chris Hinojosa, Jeremiah Zimmerman, Nathalie Neve, Derek Tretheway The 2-D velocity fields at the mid-plane of an optically trapped sphere can be obtained using the $\mu $PIVOT (Neve et al. 2008), an integrated optical tweezers (OT) and micron-resolution particle image velocimetry ($\mu $PIV) instrument. Typically, the optical trap location is centered in the $\mu $PIV measurement plane and their movements coupled. However, positioning lenses in the path of the OT laser allow the optical trap to be moved independently of the measurement plane. In order to suspend a sphere at a fixed point in space while measuring velocities around the sphere, the positioning lenses must compensate for the movement of the measurement plane. In this work, the relationship between positioning lens movement and trap location is determined by measuring the settling time of a sphere initially positioned out of focus. With this relationship determined, 2-D velocity fields are measured at different planes around a sphere in uniform flow. The measured velocity fields are compared to analytical and computational predictions to examine the effects of optical tweezers on $\mu $PIV tracer particle motion and to validate the 3-D velocity measurement potential of the $\mu $PIVOT. [Preview Abstract] |
Tuesday, November 24, 2009 9:44AM - 9:57AM |
MN.00009: Nano-Velocimetry for Nanofluidics Cuifang Kuang, Guiren Wang In order to understand physical and biological phenomena in nanoscale and build functional and practical nanofluidic devices, it is important to know the flow velocity profile. Due to the Abbe's diffraction limit barrier, traditional optical methods have so far failed in measuring the velocity profile in a nanochannel. Atomic force microscopy cannot be used for nanochannels without an opened sidewall. We have, for the first time, been able to measure the flow velocity profile for nanofluidics with a spatial resolution better than 70 nm. A novel optical point measurement method is presented, which applies Stimulated Emission Depletion (STED) to Laser Induced Fluorescence Photobleaching Anemometer (LIFPA) techniques to measure flow velocity. Herein we demonstrate this far-field nanoscopic velocimetry by measuring the velocity profile in a nanocapillary with an inner diameter of 360 nm. The closest measuring point from the wall is about 35 nm. The velocity can clearly be differentiated within just a 20 nm step, even near the axial region of the nanocapillary. This method opens up a new class of functional measuring techniques for nanofluidics and for near wall flows. [Preview Abstract] |
Tuesday, November 24, 2009 9:57AM - 10:10AM |
MN.00010: A Time-Resolved PIV with continuous Laser and High Frame Rate Camera Amir Elzawawy, Yiannis Andreopoulos Monitoring the evolution of turbulent structure using PIV requires time resolved measurements. Existing time-resolved PIV systems are limited mainly by the pulsed laser repetition rate, which currently is at about 10 KHz. In the present work we explore the possibility of using a continuous laser and a camera with a frame rate in the order of MHz, with limited number of frames. This set-up has been applied to an incompressible turbulent boundary layer flow configured in a low speed wind tunnel. In order to evaluate the technique and particularly investigate the effect of exposure time, several experiments were performed and the results compared with pulsed laser PIV and hot-wire results. Exposure times up to 15 per cent of the time between frames were used. The effect of the exposure time on the turbulence intensity was also investigated. [Preview Abstract] |
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