Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session GT: Experimental Techniques IV |
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Chair: Charles E. Tinney, University of Texas at Austin Room: 204A |
Monday, November 24, 2008 8:00AM - 8:13AM |
GT.00001: Quantitative Mixing Measurements Using MRI of the D2O, H2O System Michael Benson, Paul Mobley, Chris Elkins, John Eaton We have developed a quantitative technique for measuring the mean concentration distribution in turbulent, two-fluid mixing. The technique uses Magnetic Resonance Imaging (MRI) to study the mixing of de-ionized water, with its strong MRI signal, and heavy water, deuterium oxide with no signal. The MRI generates a 3D concentration distribution in liquids with good spatial resolution in about 10 seconds of scan time. Several repeated trials are used to obtain adequately converged statistics in turbulent flow. A qualification experiment in which water and heavy water mix in a 3D turbulent mixing layer has been completed. The full 3D concentration field is measured with MRI in a 256 X 24 X 9 array of voxels, giving a spatial resolution of 1.6 mm$^{3}$. Methanol is added at 33{\%} by volume to get a neutral density between the water and heavy water. Reynolds number based on the velocity difference and the downstream channel width is 3320. Planar Laser-Induced Fluorescence (PLIF) concentration measurements of water containing Rhodamine WT dye in place of the heavy water are used for validation and to obtain an uncertainty evaluation for the MR-based method. [Preview Abstract] |
Monday, November 24, 2008 8:13AM - 8:26AM |
GT.00002: Simultaneous Measurements of Pressure and Velocity in Gas Phase Flows via Pressure-Sensitive Microspheres Fletcher Kimura, Dana Dabiri, Gamal Khalil, Younan Xia, James B. Callis Airborne, pressure-sensitive polystyrene microspheres (PSBeads) were used to obtain simultaneous pressure and velocity measurements of gas phase flows. The PSBeads, 2.5 $\mu$m in diameter, contained a pressure-sensitive luminophor (platinum octaethylporphyrin) that was incorporated into the polymer microspheres during the polymerization process. Pressure measurements of airborne PSBeads were made using the modified Rapid Lifetime Determination method, a technique that allows for simultaneous velocity measurements using a single CCD. Work will be presented showing the titration of airborne PSBeads in gases ranging from 0 to 21\% oxygen. In addition, pressure and velocity measurements of the gas phase flow within sealed syringe will also be shown. Initial studies suggest that pressure variations as small as 10\% can be detected by the airborne PSBeads without the benefit of signal averaging. [Preview Abstract] |
Monday, November 24, 2008 8:26AM - 8:39AM |
GT.00003: Gas-phase Micro-particle Tracking Velocimetry in Millimeter-sized Channels Christopher Brotherton, Chris Bourdon This work describes a micro-Particle Tracking Velocimetry ($\mu $PTV) technique for measuring gas flows in millimeter-sized channels with low tracking particle concentrations. Compressed air flows seeded with sub-micron fluorescent particles are investigated in channels with a cross-section of 1mm x 1mm. Data are collected using a double-pulse Nd:YAG laser for lighting, a high sensitivity camera and a standard inverted microscope. Particle velocities are calculated using single frame/double exposure images and custom particle tracking software. Velocity profiles are determined for multiple locations down the channel illustrating the progression of the velocity profile within the entrance region. Maximum velocities of 6 meters per second with a measurement uncertainty of 5{\%} are measured. Currently, velocity measurements as close as 20 microns from the wall have been collected. Provided that the tracking particles are not charged, measurements even closer to the wall should be possible. Future work will examine particle velocities very near the channel walls, measure velocities in rarefied flows and provide data for simulations to determine the significance of potential particle velocity biasing in large shear and rarified conditions. [Preview Abstract] |
Monday, November 24, 2008 8:39AM - 8:52AM |
GT.00004: Data Reduction Methodology for a Turbulent High Aspect Ratio Cylindrical Flow Damien Bretall, Deborah Furey, Paisan Atsavapranee, Kimberly Cipolla, William Keith High resolution stereo-PIV measurements were made on a long ($>$ 1300 m), 38 mm diameter cylinder towed from a vertical strut at speeds of 7 to 30 kts. The experiments were performed in the high speed tow tank at NSWCCD. 3-D velocity fields were obtained. The cylinder was ballasted to be approximately neutrally buoyant and towed through a stationary laser sheet oriented perpendicular to the tow direction. The objective of the study was to quantify the boundary flow along the cylinder for correlation with simultaneous wall pressure data. Algorithms were developed to track the center of the model through the field of view to provide the spatial relation of the velocity data with the cylinder boundary. This procedure required raw image analysis and isolation of the shadow and solid body regions of the data field. This data is used to collocate subsequent image data for averaging the boundary layer velocity information along the array. Approximately 40 instantaneous vector fields were obtained for each location. Mean and fluctuating streamwise and cross-stream velocities will be presented. [Preview Abstract] |
Monday, November 24, 2008 8:52AM - 9:05AM |
GT.00005: Full elimination of nonlinear effects in a Constant Voltage Anemometer Genevi\`eve Comte-Bellot, Argantha\"el Berson, Philippe Blanc-Benon A procedure for the elimination of all nonlinearities in a Constant Voltage Anemometer (CVA) has been developed which is easily implemented on a PC when post-processing experimental data. It relies on ($1$) the first-order differential equation governing the CVA circuit, ($2$) the first-order differential equation describing the hot-wire response and ($3$) the algebraic equation corresponding to the calibration law. In practice, the method is adapted to any length of the connection cable between the hot wire probe and the CVA and only requires the extra measurement of the time constant of the hot wire using an embedded square-wave test. The present procedure aims at replacing previous data-processing methods that were mostly based on linearized equations. The two main features of the CVA, i.e. a constant bandwidth and a rapid adjustment of the hot-wire operation in the cold and hot modes to take into account temperature drifts of the incident flow, still hold when using the present method. Benefits of the new procedure are demonstrated for higher order odd moments of turbulence (skewness factors). [Preview Abstract] |
Monday, November 24, 2008 9:05AM - 9:18AM |
GT.00006: In-Cylinder IC Engine Velocity Measurements using Stereoscopic Molecular Tagging Velocimetry Reza Sadr, Mayank Mittal, Harold Schock In-Cylinder velocity field measurement is of great importance for research aimed at improvement in fuel efficiency and reduction of emissions in internal combustion (IC) engines. Application of more conventional fluid velocimetry techniques for IC measurements is, however, limited due to complex flow condition and mechanical set up in IC engines. Stereoscopic Molecular Tagging Velocimetry (SMTV) technique is used to obtain the multiple point measurement of an instantaneous three dimensional velocity field in an IC engine assembly. A novel image processing technique is implemented to obtain the velocity data. The new algorithm is computationally less expensive and eliminates the need for geometric details in earlier techniques to obtain the three-dimensional velocity components. Cycle-to-cycle variations of three dimensional velocity field and out-of-plane vorticity are presented inside the engine cylinder for three different crank angle degrees (CAD) of 90$^{\circ}$, 180$^{\circ}$, and 270$^{\circ}$. Preliminary results show high cycle-to-cycle variations in the out-of-plane velocity component but less variation is observed in the velocity component along the cylinder axis. The flow has fully three-dimensional unsteady behavior during the intake stroke; however the variations are less during the compression stroke. [Preview Abstract] |
Monday, November 24, 2008 9:18AM - 9:31AM |
GT.00007: Computing Confidence Limits on Experimental Data from the Distribution of Synthetic Data Sets Robert Downs, Edward White Multicomponent velocity measurements were obtained in a flat plate boundary layer downstream of cylindrical roughness elements using hotwire anemometry. In this configuration, the spanwise velocity (computed indirectly from the hotwire measurements) is small compared to the streamwise velocity. As a result, random and systematic errors can potentially bring about large errors in this quantity. Confidence limits are placed on the previously reported results of this experiment using Monte Carlo simulation of synthetic data sets. By introducing random perturbations to the uncertainties in estimated parameters (such as hotwire calibration coefficients), synthetic realizations of the experimental data are generated. The distribution of these realizations around the results of the actual experimental data is used to determine the level of confidence with which the experimental results are known. This technique includes the effects of covariance among different groups of uncertain parameters; as these covariances are not explicitly known the standard methods of error propagation cannot be used to accurately quantify the uncertainty of the experimental results. Finally, a quantitative comparison is made between experimental and DNS results in light of these confidence limits. [Preview Abstract] |
Monday, November 24, 2008 9:31AM - 9:44AM |
GT.00008: Microscopic Holography for flow over rough plate Siddharth Talapatra, Jiarong Hong, Yuan Lu, Joseph Katz Our objective is to measure the near wall flow structures in a turbulent channel flow over a rough wall. In-line microscopic holographic PIV can resolve the 3-D flow field in a small sample volume, but recording holograms through a rough surface is a challenge. To solve this problem, we match the refractive indices of the fluid with that of the wall. Proof of concept tests involve an acrylic plate containing uniformly distributed, closely packed 0.45mm high pyramids with slope angle of 22$^{^{\circ}}$ located within a concentrated sodium iodide solution. Holograms recorded by a 4864 x 3248 pixel digital camera at 10X magnification provide a field of view of 3.47mm x 2.32mm and pixel resolution of 0.714 $\mu $m. Due to index matching, reconstructed seed particles can be clearly seen over the entire volume, with only faint traces with the rough wall that can be removed. Planned experiments will be performed in a 20 x 5 cm rectangular channel with the top and bottom plates having the same roughness as the sample plate. [Preview Abstract] |
Monday, November 24, 2008 9:44AM - 9:57AM |
GT.00009: Unsteady Wall Shear Stress Measurements Using a Polymeric Microsphere-Based Optical Sensor Ulas Ayaz, Tindaro Ioppolo, Volkan Otugen The performance of a micro-optical wall shear stress sensor based on the whispering gallery modes (WGM) of dielectric microspheres is investigated in an unsteady flow. The sensing element is a polymeric microsphere of several hundred microns. The shear force acting on a movable plate which is flush with the wall is mechanically transmitted to the microsphere. The transmitted force perturbs the sphere's shape and refractive index leading to a shift in the optical resonances of the sphere (WGM). By monitoring these shifts, the shear force acting on the wall is measured. Unsteady wall shear stress measurements are made in a plane acoustic wave tube to investigate the bandwidth and sensitivity of the sensor prototype. By using Polydimethylsyloxane (PDMS) spheres, shear stress resolutions of $\sim $10$^{-2}$ Pa have been measured experimentally. [Preview Abstract] |
Monday, November 24, 2008 9:57AM - 10:10AM |
GT.00010: Global Oxygen Sensing and Visualization in Water using Luminescent Probe on Anodized Aluminum Tatsuya Ozaki, Hitoshi Ishikawa, Yoshimi Iijima, Hirotaka Sakaue The extension of pressure-sensitive paint (PSP) technique as a wind tunnel technology to a global oxygen visualization and detection in water is presented. The topic includes the development of anodized-aluminum pressure-sensitive paint (AA-PSP) as a global oxygen sensor in water as well as its calibration and demonstration. Based on the luminophore study, platinum porphyrin is selected as a luminophore, because it is not dissolved in water. It is found that the luminescent increase is over 20 percent after 8 days immersed in water. Even though the signal increases after water immersion, its oxygen sensitivity is the same, which is 0.4. This AA-PSP is used to visualize oxygen rich water (20 mg/l) impinged in less oxygen water (3 mg/l). Even though the difference of water is only the amount of oxygen, we can visualize the water jet with its mixing process using a fast frame rate camera at the frame rate of 100 Hz. In the final version, we will include the oxygen map combined with the visualization result. [Preview Abstract] |
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