Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session KH: Experimental Techniques: Particle-Based Anemometry |
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Chair: Candace Wark, Illinois Institute of Technology Room: Hilton Chicago Williford B |
Monday, November 21, 2005 4:10PM - 4:23PM |
KH.00001: Energy dissipation rate measurements with PIV-PTV in a Partially Stirred Reactor (PaSR) Luminita Danaila, Paul Dimotakis, Bruno Renou, Jean-Francois Krawczynski The work presented addresses some of the questions surrounding the experimental determination of the mean energy dissipation rate. The approach is based on a hybrid PIV-PTV (particle-tracking velocimetry) method. The flow investigated is in a Partially Stirred Reactor (PaSR) in which fluid is injected through 16 opposed jets that issue from top/bottom planes. PIV is first used to detect a locally averaged mean velocity of particle groups. A refined PTV algorithm is then used, with a resolution of $\sim $1 pixel, to determine the instantaneous, spatially resolved velocity field. Second-order structure functions are calculated as a function of spatial separation. Their small-scale limit provides estimates for the mean energy dissipation rate that are in good agreement with ones obtained from the inertial range of scales or very large scales (the last two are not affected by resolution). Three different methods allow for a proper determination of the dissipation rate, which is found to be 20 {\%} greater than that inferred from PIV alone. Our results suggest an improved methodology for the estimation of instantaneous values and high-order, small-scale, velocity-field statistics. [Preview Abstract] |
Monday, November 21, 2005 4:23PM - 4:36PM |
KH.00002: Development of a PIV based technique for measurements of instantaneous pressure distributions Xiaofeng Liu, Joseph Katz A non-intrusive PIV based method for measuring the instantaneous pressure distribution over a sample area simultaneously with the velocity field has been developed and tested. This method utilizes four-exposure PIV measurements to measure the distribution of material acceleration, and then integrating it to obtain the pressure. Two cameras are used, one for recording images 1 and 3, and the other for recording images 2 and 4. Validation tests of the principles of the technique using synthetic images of rotating and stagnation point flows show that the standard deviation of the measured pressure from the exact value can be kept within 1.0{\%}. A key to the success of this method is precision matching of images recorded by the two cameras. Images of stationary particles recorded at the same time are used for generating a map of local deformations for matching the two filed of views. Application of local image deformation correction to velocity vectors measured by the two cameras reduces the error due to misalignment and image distortion to about 0.01 pixels. An efficient and accurate acceleration integration algorithm has also been developed. This method has been used for measuring the instantaneous pressure distribution in a cavity shear flow, and samples will be presented. [Preview Abstract] |
Monday, November 21, 2005 4:36PM - 4:49PM |
KH.00003: Experimental investigation of low Mach number flow past a rectangular cavity using dual-camera Cinematographic PIV system Shiyao Bian, Steven Ceccio, James Driscoll Flow past cavity has been of interest due to its geometrical simplicity and complex flow characteristics. A dual-camera Cinematographic Particle Image Velocimetry (CPIV) system has been developed to study low Mach number flow over a rectangular cavity. This system consists of two high-repetition rate Nd:YAG lasers and two high-speed CMOS cameras registered to have sub-pixel alignment errors. A rectangular cavity with a length-to-depth ratio of 2 was mounted in the test section of a recirculating water tunnel providing free-stream flow speeds between 5$\sim $26 m/s. Consecutive CPIV images with a spatial resolution of 1632 x 800 pixels and 20 $\mu $s time delay were obtained at frame rate of 1.5 KHz. Time traces of surface pressures at the bottom of the cavity are acquired simultaneously by using flush-mounted dynamic pressure transducers. The temporal evolution of velocity and vortical fields reveals the time-dependence of the mixing and mass transport between the shear layer and the cavity. The simultaneous velocity and pressure measurements also show the unsteady interaction between vortical structures and the trailing edge of the cavity under resonating and non-resonating conditions. [Sponsored by National Science Foundation Grant: CTM 0203140] [Preview Abstract] |
Monday, November 21, 2005 4:49PM - 5:02PM |
KH.00004: Cinematographic 3-D PIV of a Turbulent Jet Noel T. Clemens, Bharathram Ganapathisubramani, Krishna Lakshminarasimhan The structure of a fully developed turbulent jet at a Reynolds number of 5000 is investigated with cinematographic (1 kHz) stereoscopic PIV in a plane normal to the jet axis (i.e., ``end view''). The temporal resolution is sufficiently high that Taylor’s hypothesis can be used to enable the computation of velocity gradients in the axial direction. Furthermore, the resolution (in space and time) is approximately three Kolmogorov scales, and is therefore sufficient to resolve the structure of the dissipation field. The technique enables computation of all terms of the velocity gradient tensor in a plane, at kilohertz rates, and therefore at each point in the plane we can compute the complete vorticity vector, strain rate tensor and kinetic energy dissipation. We use the data to investigate the time-evolution of the dissipation field and its relationship to the vorticity and strain rate fields. The data can alternatively be used to form y-z-t volumes (with x the axial direction). These pseudo-volumes show that the vorticity field is dominated by tube-like structures and the dissipation structures are often sheet-like or more nondescript “blobs”. The spatial relationship among the dissipation, strain rate and vorticity will be discussed, as well as a statistical analysis of these quantities. [Preview Abstract] |
Monday, November 21, 2005 5:02PM - 5:15PM |
KH.00005: WITHDRAWN: Use of Variable Thresholds in Post-Correlation PIV Outlier Correction Dana Dabiri, Adi Salehuddin While PIV has successfully proven to be a valuable velocity measurement technique, it has still been susceptible to producing outliers due to a variety of reasons. Many methods of correcting these post-correlation outliers have been proposed with varying degrees of success. This paper proposes a method of correction using automated variable thresholds to identify and replace outliers. This method varies the threshold depending on the velocity around the node of interest, and utilizing statistical properties such as averages, and standard deviations to identify the local threshold value. This allows the threshold to better accommodate the changes in the velocity profile of a specific region. This method will be applied to simulated velocity profiles containing outliers, and the results will be compared with a fixed threshold method. [Preview Abstract] |
Monday, November 21, 2005 5:15PM - 5:28PM |
KH.00006: Improving the spatial resolution of particle image velocimetry by means of weighting window functions Holger Nobach, Nicholas T. Ouellette, Eberhard Bodenschatz Due to its high robustness, correlation-based particle image velocimetry (PIV) has become the prime choice for processing image-based flow measurements in fluid dynamics experiments. The algorithm-inherent averaging process over certain image subspaces limits the achievable spatial resolution. By utilizing appropriate weighting window functions in an iterative refinement loop, the spatial resolution can be improved significantly. We will prove the concept by investigating the achievable stability and spatial resolution given by the frequency response function for different windowing functions. An algorithm that implements the windowing concept will be introduced yielding a densely sampled estimate of the velocity field. The ability of the entire procedure to improve the spatial resolution is shown using a simulated flow field with high velocity gradients. [Preview Abstract] |
Monday, November 21, 2005 5:28PM - 5:41PM |
KH.00007: Random error due to Brownian motion in particle image velocimetry Christopther Bourdon, Michael Olsen In particle image velocimetry (PIV) experiments, the Brownian motion of seed particles results in the addition of a random error component to the measured velocity. As the number of seed particles within each control volume increases, this random error component will decrease. Previous researchers have assumed that this random error decreases proportionally with the square root of the number of seed particles in the measurement volume as the central limit theorem predicts. However, this conclusion is based on the assumption that each seed particle contributes equally to the measured velocity, which is not the case in PIV. This assumption is even further weakened in micro-PIV experiments, where the contribution of individual particles is dependent on their separation from the image plane, due to volume rather than sheet illumination. In the present work, a computer simulation of volume-illuminated and sheet-illuminated particle-image interrogation for flowfields with a Brownian motion component was performed for various experimental conditions to determine the proper relationship between seed particle density and random error due to Brownian motion. It was found that the actual random error is greater than that predicted by application of the central limit theorem. To assist in the design and analysis of PIV experiments, an empirical formula for estimating error in micro and standard PIV experiments with Brownian motion is presented. [Preview Abstract] |
Monday, November 21, 2005 5:41PM - 5:54PM |
KH.00008: A novel 3D micron-scale DPTV (Defocused Particle Tracking Velocimetry) and its applications in microfluidic devices John Roberts, Qian Liao, Joseph D. Kirtland, Bradley Morgenfeld, Abraham Stroock, Mingming Wu The rapid advancements in micro/nano biotechnology demand quantitative tools for characterizing microfluidic flows in lab-on-a-chip applications, validation of computational results for fully 3D flows in complex micro-devices, and efficient observation of cellular dynamics in 3D. We present a novel 3D micron-scale DPTV (defocused particle tracking velocimetry) that is capable of mapping out 3D Lagrangian, as well as 3D Eulerian velocity flow fields at sub-micron resolution and with one camera. The main part of the imaging system is an epi-fluorescent microscope (Olympus IX 51), and the seeding particles are fluorescent particles with diameter range 300nm - 10um. A software package has been developed for identifying (x,y,z,t) coordinates of the particles using the defocused images. Using the imaging system, we successfully mapped the pressure driven flow fields in microfluidic channels. In particular, we measured the Laglangian flow fields in a microfluidic channel with a herring bone pattern at the bottom, the later is used to enhance fluid mixing in lateral directions. The 3D particle tracks revealed the flow structure that has only been seen in numerical computation. This work is supported by the National Science Foundation (CTS - 0514443), the Nanobiotechnology Center at Cornell, and The New York State Center for Life Science Enterprise. [Preview Abstract] |
Monday, November 21, 2005 5:54PM - 6:07PM |
KH.00009: 3D-flow measurements in micro channel and pipe with high time resolution using micro digital-holographic particle-tracking velocimetry Shin-ichi Satake, Tomoaki Kunugi, Kazuho Sato, Tomoyoshi Ito, Jun Taniguchi, Hiroyuki Kanamori A micro digital-holographic particle-tracking velocimetry (micro-DHPTV) method for high time-resolution flow field measurement in a micro-channel was developed by Satake et al. (2005). The system consists of an objective lens, a high-speed camera and a single high-frequency double pulsed laser. Particle positions in a three-dimensional field can be reconstructed by a computer-generated hologram. The time evolution of a three-dimensional water flow in a semicircular micro-channel of 100-$\mu$m width and 40-$\mu$m depth and in a circular micro-pipe of 100-$\mu$m inner diameter are obtained successfully using this micro-DHPTV system. The three- dimensional measurement volume of the system is 410 $\mu$m $\times$ 100 $\mu$m $\times$ 40 $\mu$m and is irradiated by one laser beam with the time resolution of 100 $\mu$sec and a reputation rate of 1 kHz. Consequently, 130 velocity vectors in the semicircular micro-channel can be obtained instantaneously. Satake, S., Kunugi, T., Sato, K., Ito T., Taniguchi, J., ``Three- dimensional flow tracking in a micro channel with high time resolution using micro digital-holographic particle-tracking velocimetry,'' To appear in Optical Review, 2005. [Preview Abstract] |
Monday, November 21, 2005 6:07PM - 6:20PM |
KH.00010: Measurements of 3-D Flows with a Digital Holographic Microscope E. Malkiel, J. Sheng, J. Katz Rising interests in micro-scale dynamics, such as turbulence in a near wall region or flow around a microorganism require measurements at compatible scales. A Digital Holographic Microscope (DHM) records magnified in-line holographic images and the 3D volumes are reconstructed numerically. This method offers inherent advantages over both conventional microscopy and lens-less in-line holography. DHM extends the depth of field of a conventional microscope by two orders of magnitude, to about 1000 time the target object diameter. It also reduces the depth-of-focus to less than ten particle diameters, two orders of magnitude lower than lens-less holography. For example, using segmentation and volume averages, one can detect displacements of 2$\mu $m particles in the depth direction at a resolution of about 10 $\mu $m. A single digital hologram can detect 5000 -- 10,000 particles. Examples of implementation of this method include near-wall velocity measurements of the channel flow at 0$<$y$^{+}<$60 (Re$_{h}$=60,000), as well as swimming behavior of a nauplius. Errors and techniques for determining velocity field and particle distributions are discussed. [Preview Abstract] |
Monday, November 21, 2005 6:20PM - 6:33PM |
KH.00011: Measurement of high-speed water column inside a Steam Injector using Dynamic PIV Koji Okamoto, George Kuwabara, Sunao Narabayashi, Michitsugu Mori The Steam Injector is the superior system to pump the fluid without rotating machine. Because the water column is surrounded by the saturated steam, very high heat transfer is also expected with direct condensation. The inside of the Steam Injector is very complicated. To improve the efficiency of the Steam Injector, the water column behavior inside the Injector is visualized using the Dynamic PIV system. Dynamic PIV system consists of the high-speed camera and lasers. In this study, 384x180 pixel resolution with 30,000fps camera is used to visualize the flow. For the illumination CW green laser with 300mW is applied. To view inside the Injector, relay lens system is set at the Injector wall. Very high speed water column during the starting up of Steam Injector had been clearly visualized with 30,000fps. The wave velocity on the water column had been analyzed using PIV technique. The instability of the water column is also detected. [Preview Abstract] |
Monday, November 21, 2005 6:33PM - 6:46PM |
KH.00012: Comparison of Data from Three PIV Configurations for a Supersonic Jet in Transonic Crossflow Steven Beresh, John Henfling, Rocky Erven, Russell Spillers Particle image velocimetry (PIV) data have been acquired using three different configurations in the far-field of the interaction of a transverse supersonic jet with a transonic crossflow. The configurations included two-dimensional PIV in the centerline streamwise plane at two overlapping stations, as well as stereoscopic PIV in both the same streamwise plane and the crossplane. The streamwise data show the downstream evolution of the interaction whereas the crossplane data directly reveal its vortex structure. The measurement planes intersect at a common line, allowing a comparison of those mean velocity components and turbulent stresses common to all configurations. All data from the streamwise plane agree to within their estimated uncertainties, but data from the crossplane exhibit reduced velocity and turbulent stress magnitudes by a small but significant degree. Additionally, the vertical positions of the peak velocities are slightly nearer the wall for the crossplane configuration. This comparison suggests that routine methods of uncertainty quantification for data used in the validation of computational models may not fully capture the error sources of an experiment. [Preview Abstract] |
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