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 EN: Experimental Techniques III: Scalar |
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Chair: John Eaton, Stanford University Room: 200C |
Sunday, November 22, 2009 4:15PM - 4:28PM |
EN.00001: Lifetime Based Temperature and Velocity Measurement using High-Speed Camera and Temperature Sensitive Particles Satoshi Someya, Mitsunori Uchida, Kaoru Tominaga, Keiko Ishii, Yanrong Li, Koji Okamoto A simultaneous measurement technique of velocity and temperature distribution in a fluid flow was developed. Particle image velocimetry (PIV) was combined with a lifetime based scalar measurement technique. A measurement method based on the luminescent lifetime is appropriate for detecting the transient temperature field. Developed method needs a high speed camera, a laser (one excitation wave length) and temperature sensitive particles (TSParticles). The luminescence from TSParticles doped with EuTTA was detected by the high speed camera, which was not equipped with any image intensifier, at 15000 frames per second. Imaging at the high frame rate has a possibility to carry out PIV with a wide dynamic range. A decay of luminescent intensity was detected in detail. The decay curves at various temperature conditions were fitted well to exponential functions, from which the decay constant at each temperature was obtained. The proposed technique was applied to measure the temperature and the velocity field in a natural convection driven by Marangoni force and by buoyancy in a rectangular tank. The accuracy of the temperature measurement of the proposed technique was $\pm$0.5$^{\circ}$C. [Preview Abstract] |
Sunday, November 22, 2009 4:28PM - 4:41PM |
EN.00002: Magnetic Resonance Imaging Measurements of Film Cooling Effectiveness Christopher Elkins, Marcus Alley, John Eaton Film cooling through holes and slots is used extensively in gas turbine engines to protect combustor walls, stator vanes, and turbine blades. Film cooling effectiveness has been shown to depend on myriad geometrical and flow parameters. Magnetic Resonance Velocimetry (MRV) and Concentration (MRC) measurements efficiently acquire entire 3D velocity and scalar information making them well suited to investigate the large design parameter space. In addition, MRV and MRC provide information in the film supply plenum and hole which is traditionally unobtainable. Here, MRC is extended to near wall measurements to determine film cooling effectiveness. Measurements are made for a single film hole (d=5.8 mm, l/d=4 and $\alpha $=30\r{ }) in the wall of a square channel. Velocity and scalar concentration data are presented for multiple blowing ratios. The data show the evolution of vortices around the jets, the coolant mixing, and the 2D film cooling effectiveness distribution. Measurements within the plenum and injection hole show the origin of specific flow structures. [Preview Abstract] |
Sunday, November 22, 2009 4:41PM - 4:54PM |
EN.00003: Validation of LES predictions with Microscopic Particle Image Velocimetry in an axial symmetric Confined Impinging Jets Reactor Emmanuela Gavi, Matteo Icardi, Daniele Marchisio, Michael G. Olsen, Rodney O. Fox, Djamel Lakehal Micromixer devices, such as the Confined Impinging Jets Reactor (CIJR) are under study, in particular for micro- and nanoparticles precipitation processes. In this work the flow field in an axial symmetric CIJR was studied by means of microscopic Particle Image Velocimetry (microPIV), an innovative experimental technique that allows to measure the instantaneous flow field over a global domain. Experimental measurements were carried out at four flow rates, ranging from quasi-steady laminar to unsteady turbulent regime. To the authors knowledge this work is the first one to report experimental microPIV data on an axial symmetric microscopic device. Measurements were then employed to validate predictions obtained with Large Eddy Simulation (LES). CFD results were able to reproduce the instability of the flow observed in the CIJR and a good quantitative agreement is found for both the mean velocity components and the fluctuations. An interesting result of this study is the understanding of the necessity of mimic the pumping instability in LES simulations of the CIJR, by imposing appropriate inflow boundary conditions, which contribute to determine the unsteady behavior of the flow. [Preview Abstract] |
Sunday, November 22, 2009 4:54PM - 5:07PM |
EN.00004: Visualization of turbulent reacting flow in a microscale nanoprecipitation reactor Yanxiang Shi, Somashekar Vishwanat, Michael Olsen, Rodney Fox A flow visualization technique using the pH sensitive dye phenolphthalein was used to visualize and quantify turbulent reacting mixing in a microscale nanoprecipitation reactor. Phenolphthalein is colorless at pH lower than 8, but turns pink at higher pH, making it useful for visualizing acid-base reactions. Using this dye, turbulent reactive mixing in a confined impinging jets reactor (CIJR) was investigated. The reactor has two inlet streams, one at a pH of 3, and the other at a pH of 11. Phenolphthalein is also dissolved in both streams. A flash lamp with a extremely short pulse duration is used to freeze the turbulent motion of the fluids, and images are captured using a video camera. Quantitative mixing data are obtained by using a thresholding technique where local image intensities are transformed to binary signals which represent the local pH: 0 stands for pH lower than 8 and 1 for pH higher than 8. For each Reynolds number under consideration, thousands of realizations are acquired. Using this thresholding technique, probability density functions are obtained, allowing comparison to numerical simulations. [Preview Abstract] |
Sunday, November 22, 2009 5:07PM - 5:20PM |
EN.00005: Determination of Plasma Electron Density from Optical Measurements Brian Neiswander, Eric Matlis, Thomas Corke Plasma has been shown to be effective in many flow control applications, but now may also find use in adaptive optics. Plasma's index of refraction is coupled with it's electron density which may be adjusted for adaptive control. An experimental setup to verify the relation between plasma electron density, pressure, and voltage is presented. A non-thermal DBD plasma cell is created by evacuating air and applying a voltage potential between two conducting glass slides. Plasma forms in the chamber between the glass and the applied voltage potential controls the electron density. A HeNe laser is passed through the plasma cell and then focused onto a duo-lateral position sensing device (PSD). The plasma cell is oriented at an angle to the laser's beam and so changes in the plasma's index of refraction produce lateral translations in the beam position. Differences in the PSD output with and without plasma provides for the calculation of the electron density averaged over the beam spot area. The data from this experiment will be used to further develop an adaptive plasma lens for wavefront aberration corrections. [Preview Abstract] |
Sunday, November 22, 2009 5:20PM - 5:33PM |
EN.00006: Photochemistry of tracers used for molecular tagging diagnostics R. Nehe, R. Basu, A.M. Naguib, M.M. Koochesfahani Phosphorescence characteristics of molecular tracers are important to certain class of molecular tagging diagnostics, including the recently demonstrated technique of molecular tagging manometry (MTM). The photoluminescence of tracers acetone and biacetyl are studied in an effort to understand the factors affecting their phosphorescence lifetime. The phosphorescence emission of these tracers is known to be strongly quenched by oxygen. Here we present a more complete picture of quenching by accounting for the effects of self-quenching, in addition to oxygen quenching. It is found that acetone self quenching explains the factor of order ten reduction in lifetime observed in our oxygen-free experiments. Biacetyl phosphorescence, on the other hand, is not significantly affected by self quenching. The order of magnitude reduction in biacetyl lifetime measured in our oxygen-free experiments is connected to triplet-triplet annihilation reaction occurring at high intensities of the excitation light. [Preview Abstract] |
Sunday, November 22, 2009 5:33PM - 5:46PM |
EN.00007: Design Feasibility Study of Whole-Field Pressure Measurements in Gas Flows: Molecular Tagging Manometry (MTM) M.M. Koochesfahani, R. Basu, A.M. Naguib We present the theoretical foundation, implementation framework and experimental demonstration of a new diagnostic technique for non-intrusive, whole-field measurement of pressure within gasses. The new technique, which is referred to as Molecular Tagging Manometry (MTM), relies on oxygen quenching of phosphorescence emission from photo-excited tracers in oxygen-containing gases. As the pressure increases, the density of oxygen becomes larger, leading to a shorter emission lifetime: a working principle that is similar to pressure sensitive paint (PSP) but applied within the body of the flow. Using an experimental apparatus that is built around a pressure vessel, the viability of MTM is demonstrated for the first time using acetone as a tracer. [Preview Abstract] |
Sunday, November 22, 2009 5:46PM - 5:59PM |
EN.00008: Liquid crystal thermometry for micro-fluidic applications Tait Pottebaum Liquid crystal thermometry has been implemented in a micro-channel and the performance of the technique quantified. Implementation of the technique is subject to constraints on imaging and illumination configurations similar to the constraints on micro-PIV. In addition, the proximity of the measurements to interfaces and surfaces from which light scatters leads to high noise levels that cannot be reduced by wavelength filtering (such as with fluorescent particles) because the temperature information is contained in the color of the particles. Therefore, circular polarization filtering is used, exploiting the circular dichroism of the thermochromic liquid crystal (TLC). Encapsulated TLC particles were flowed through the micro-channel and subjected to a series of uniform temperatures for calibration. To validate the technique, a temperature gradient was imposed with no flow. Finally, the technique was applied to micro-channel flow with an imposed wall temperature gradient in the flow direction. Liquid crystal thermometry can now be applied to a wide range of micro-fluidic applications. [Preview Abstract] |
Sunday, November 22, 2009 5:59PM - 6:12PM |
EN.00009: Effect of Experimental Parameters and Image Noise on the Error Levels in Molecular Tagging Velocimetry/Thermometry (MTV/T) Jianghua Ke, Douglas Bohl In this work the effect of experimental parameters on the error levels associated with simultaneous measurement of velocity and temperature using Molecular Tagging Velocimetry/Thermometry (MTV/T) are quantified via simulated images. Images were simulated using Gaussian profile laser lines. Noise was added to the images using a uniform random distribution and a Gaussian random distribution to simulate electronic noise and shot noise respectively. The results showed that the error levels in the velocity and temperature measurements were inversely related for most experimental parameters including the laser line thickness, fluid temperature and image delay times. It is concluded that the dynamic range of the technique depends on the flow speeds and temperatures and must be determined for each experiment individually. Error levels, for 95{\%} confidence, were found to be better than 0.3$^{\circ}$ C for temperature and 0.2 pixels for velocity given typical experimental parameters. [Preview Abstract] |
Sunday, November 22, 2009 6:12PM - 6:25PM |
EN.00010: Measuring near-wall temperatures using dual-tracer fluorescence thermometry and evanescent-wave illumination Myeongsub Kim, Minami Yoda Fluorescence thermometry measures liquid temperatures based on changes in fluorescence intensity. Dual-tracer (or ratiometric) fluorescence thermometry (DFT) improves the accuracy of FT by taking the ratio of the emissions from two different fluorescent species excited at the same wavelength by the same illumination, thereby removing changes in fluorescence intensity due to spatial variations in the excitation. Moreover, DFT using two species with opposite temperature sensitivities can significantly increase the sensitivity of the technique. The ratio of the signals from an aqueous solution of fluorescein (Fl) and sulforhodamine B (SrB), which have intensities that increase and decrease, respectively, when volumetrically illuminated at 514 nm, varies by as much as 7{\%} per \r{ }C for fluid temperatures $T$ = 15-60 \r{ }C. The method has experimental uncertainties, based on temperature calibrations obtained with volume illumination, of $\pm $1.1 \r{ }C and $\pm $0.3 \r{ }C at spatial resolutions of 3.7 $\mu$m and 30 $\mu$m, respectively. This talk describes extending DFT to near-wall temperature measurements by using evanescent-wave illumination to measure fluid temperatures averaged over about the first 0.5 $\mu$m next to the wall, or in most cases, the wall surface temperature. [Preview Abstract] |
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