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 A16: Experimental Techniques I |
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Chair: Steve Wereley, Purdue University Room: 319 |
Sunday, November 20, 2011 8:00AM - 8:13AM |
A16.00001: An experimental investigation of the influence of particle displacement and image number on PIV uncertainty for two turbulent flows Ralph Budwig, Christopher Hocut In order to test sensitivity to particle displacement, the mean velocity and turbulent fluctuations were calculated from six sets of stereoscopic PIV images, each with a different average particle displacements. The first set of images had an average particle displacement of five pixels and in each subsequent set the displacement was increased by five pixels. In order to test sensitivity to image number, the number of images used for ensemble averaging was varied from 1000 to 4000 The first flow tested was a nearly fully developed turbulent open channel flow (moderate turbulence levels). The second was the turbulent wake immediately behind a circular cylinder that extended from just above the channel bottom through the water free surface (high turbulence levels). Comparisons to ADV measurements were made at selected points in both flows. $^{1}$Center for Ecohydraulics Research $^{2}$Environmetnal Fluid Dynamics Laboratory [Preview Abstract] |
Sunday, November 20, 2011 8:13AM - 8:26AM |
A16.00002: ABSTRACT WITHDRAWN |
Sunday, November 20, 2011 8:26AM - 8:39AM |
A16.00003: A postprocessing method for finding flow derivatives on an unstructured grid using PTV data Micah Paul, Dana Dabiri Existing methods of processing particle tracking velocimetry (PTV) data to determine derivative information, such as shear and vorticity, require that the scattered velocity data be interpolated onto a uniform grid. While this makes calculations of flow derivatives simple, it necessarily introduces error. Here, a process is proposed which allows for the calculation of differential properties on unstructured grids. The proposed method first uses an anisotropic diffusion smoothing technique to denoise the velocity data, and then uses a natural neighbors-based Laplace interpolation to calculate local velocity derivatives. Results using this technique are discussed. [Preview Abstract] |
Sunday, November 20, 2011 8:39AM - 8:52AM |
A16.00004: 3 dimension 3 coordinate velocity measurements of electrothermal vortex using Interference micro Particle Tracking Velocimetry Craig Snoeyink, Steve Wereley We present velocity measurements of an electrothermal vortex using Interference micro Particle Tracking Velocimetry (I-$\mu$PTV). These measurements are compared to results obtained using Astigmatism micro-Particle Tracking Velocimetry (A-$\mu$PTV). We will also demonstrate several of the advantages of this system such as an increased measurement volume thickness as well as the ability to use small particles ($<$ 1 $\mu$m diameter). [Preview Abstract] |
Sunday, November 20, 2011 8:52AM - 9:05AM |
A16.00005: Color-Coded Three-Dimensional Particle Tracking Velocimetry for Micro-Flow Applications Wei-Hsin Tien, Dana Dabiri, Jay Hove A color-coded three-dimensional particle image velocimetry is successfully adapted into a microscope setup using a 10X magnification lens.~ 3 high-power LED with different wavelengths are used as light sources for each color-coded pinhole, and a color separation algorithm based on decorrelation stretch is developed to account for the multiple exposure problem caused by the color filters.~ Overlapped particle images are then identified with a cascade correlation method, and the triplets are matched to reconstruct the 3D particle locations with a calibration-based epi-polar line search method. The velocity field is reconstructed by a vision-based particle tracking algorithm. With the ability to tack particles in higher particle densities, the experimental setup is used to image an 800 x 800 x 500 micrometer volume of an accelerating backward-facing step micro-channel flow. [Preview Abstract] |
Sunday, November 20, 2011 9:05AM - 9:18AM |
A16.00006: Split view Time-resolved PIV with a CW laser for 3-D measurements of planar velocity field Amir Elzawawy, Yiannis Andreopoulos The demand to increase the temporal resolution of Stereo-PIV systems used in the measurement of highly unsteady flow fields is limited by the low repetition rate of the pulsed lasers and cameras. The availability of high-frame-rate digital cameras and CW lasers opens new possibilities in the development of continuous PIV systems with increased temporal resolution. The present setup consists of a single high-frame-rate camera which can accommodate two simultaneous stereo view images of the deforming fluid on its CMOS sensor obtained by using four different planar mirrors, appropriately positioned This approach offers several advantages over traditional systems with two different cameras. First, it provides identical system parameters for the two views which minimize their differences and thus facilitating robust stereo matching. Second, it eliminates any need of synchronization between both cameras and the laser. And third its cost is substantially lower than the cost of a system with two cameras. The development of the technique will be described and the results of qualification tests in several wind tunnel flows will be presented and discussed. [Preview Abstract] |
Sunday, November 20, 2011 9:18AM - 9:31AM |
A16.00007: Accuracy of standard image processing and PIV analysis applied to x-ray velocimetry Elizabeth Voigt, Roderick La Foy, Kamel Fezzaa, Wah-Keat Lee, Pavlos Vlachos Particle image velocimetry (PIV) using x-ray illumination is a recently developed technique providing a new capability to study low-Reynolds number opaque flows such as blood flow in microvessels. Preliminary work in x-ray PIV by several groups has used image processing and PIV techniques originally developed for optical PIV images, although significant differences exist between standard PIV images and x-ray PIV images. This work quantitatively assesses the validity of standard image processing and PIV techniques for x-ray images. Data were acquired for steady Poiseuille flow using hollow glass microspheres as tracers. Images were pre-processed using techniques including mean subtraction, Fourier filter, phase retrieval, and inversion filter, and velocity fields were computed using standard cross-correlation and robust phase correlation. A metric of image quality was found that reliably predicts the best of the pre-processed image sets. Quantitative comparison of velocity profiles with the Poiseuille solution indicated that robust phase correlation outperforms standard cross correlation for x-ray images. [Preview Abstract] |
Sunday, November 20, 2011 9:31AM - 9:44AM |
A16.00008: Developing an ultrasound correlation velocimetry system Gerrit Surup, Christopher White The process of building an ultrasound correlation velocimetry (UCV) system by integrating a commercial medical ultrasound with a PC running commercial PIV software is described and preliminary validation measurements in pipe flow using UCV and optical particle image velocimetry (PIV) are reported. In principles of operation, UCV is similar to the technique of PIV, differing only in the image acquisition process. The benefits of UCV are that it does not require optical access to the flow field and can be used for measuring flows of opaque fluids. While the limitations of UVC are the inherently low frame rates (limited by the imaging capabilities of the commercial ultrasound system) and low spatial resolution, which limits the range of velocities and transient flow behavior that can be measured. [Preview Abstract] |
Sunday, November 20, 2011 9:44AM - 9:57AM |
A16.00009: Power Spectrum Estimation of Randomly Sampled LDA Signals Preben Buchhave, Clara Velte, William George Power spectra from LDA data must be computed using the theory of burst-mode LDA processing in which the sampling bias is corrected by means of the measured residence time [1,2]. However, the validity of this method has been disputed, and alternative methods have been proposed, partly on theoretical grounds, partly with reference to practical problems with the measurement of the residence time [3]. We present power spectra computed by a number of different algorithms (i.a. the block averaged direct spectral estimator, the Fourier transform of the slotted autocovariance estimate and the sample-and-hold method) using simulated data from 3-D turbulent velocity, and we show that only residence time weighted algorithms give the correct answer in all situations. We also demonstrate clearly effect of using the wrong algorithms by processing some single frequency spectra. We confirm these conclusions by evaluating power spectra from a turbulent jet [4]. The power spectra from the jet data show good agreement with the results from simulated data. [1] Buchhave, Ph.D dissertation 1979 [2] Buchhave, George and Lumley, Ann. Rev. Fluid Mech. 1979 [3] Albrecht, Borys, Damaschke and Tropea, Springer Verlag pp. 552, 2003 [4] Velte, Ph.D. dissertation 2010 [Preview Abstract] |
Sunday, November 20, 2011 9:57AM - 10:10AM |
A16.00010: An Experimental Investigation on the Wake Interference of Multiple Wind Turbines over Complex Terrains Hui Hu, Zifeng Yang, Ahmet Ozbay, Partha Sarkar We report an experimental study to investigate the wake interferences of multiple wind turbines sited over complex terrains in order to elucidate underlying physics to explore/optimize design paradigms of wind turbines sited over complex terrains for higher power yield and better durability. The experiments were conducted in a wind tunnel with an array of wind turbine models sited over a flat (baseline case) and complex terrains with non-homogenous surface winds. In addition to measuring dynamic wind loads (both forces and moments) and the power outputs of the wind turbine models, advanced flow diagnostic techniques such as digital Particle Image Velocimetry (PIV) will be used to conduct detailed flow field measurements to quantify the flow characteristics of the surface winds and wake interferences among multiple wind turbines over flat (baseline case) and complex terrains. The detailed flow field measurements were correlated with the wind load measurements to elucidate the underlying physics associated with turbine power generation and fatigue loads acting on wind turbines. [Preview Abstract] |
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