Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session R29: Experimental Techniques: Data Analysis and Particle Tracking |
Hide Abstracts |
Chair: Brian Elbing, Oklahoma State University Room: 2014 |
Tuesday, November 25, 2014 1:05PM - 1:18PM |
R29.00001: Uncertainty analysis of planar laser-induced fluorescence measurements Stavros Tavoularis, Christina Vanderwel We present a thorough analysis of the uncertainty of the planar laser-induced fluorescence (PLIF) method. We consider the measurement of concentration maps in cross-sections parallel to and normal to the axis of a slender plume containing Rhodamine 6G as a passive scalar tracer and transported by a turbulent shear flow. In particular, we identify two previously unexplored sources of error contributed by non-uniformity of the concentration across the laser sheet and by secondary fluorescence. We propose new methods to evaluate and correct for these sources of error and demonstrate that the corrected concentration measurements accurately determined the injected dye mass flow rate of the plume in the far field. [Preview Abstract] |
Tuesday, November 25, 2014 1:18PM - 1:31PM |
R29.00002: Revisiting George, 1978: When are velocity samples independent? Barton Smith It is well known that the standard deviation of the mean of a sample is the standard deviation of the parent population divided by the square root of the number of samples, assuming the samples are independent. In 1978, William George [1] suggested that the sampling period must be greater than two integral time scales T$_{\mathrm{u}}$ to ensure independent samples in turbulent flow. This time scale is defined as the integral over all time of the autocorrelation of the velocity signal. In the present work the velocity in a turbulent rectangular incompressible jet was measured using a single calibrated hot-wire probe with sampling periods above and below 2 T$_{\mathrm{u}}$. To determine T$_{\mathrm{u}}$, 11 sets of 100,000 data points were acquired at high rate. Each set was divided into 50 records of 2000 points. The autocorrelation $\rho $, was computed for each record, and the 550 results were averaged together. T$_{\mathrm{u}}$ was computed by integrating $\rho $ form 0 to the time where $\rho $ became negative. Returning to the same flow, data were acquired at rates above and below those recommended by George. It is found that even at 8 times the rate recommended by George, the mean converged at a rate of 1/sqrt(N) [although the error was larger than S/sqrt(N)] and that at sampling period of 2T$_{\mathrm{u}}$ the error in the mean was well predicted by S/sqrt(N). However, sampling slower resulted in a smaller mean error. \\[4pt] [1] William K. George Jr. Processing of random signals. In \textit{The Dynamic Flow Conference} 1978 on Dynamic Measurements in Unsteady Flows, pages 757--800, 1978. [Preview Abstract] |
Tuesday, November 25, 2014 1:31PM - 1:44PM |
R29.00003: Measurement uncertainty quantification: comparison of time-varying uncertainty with error Bernhard Wieneke, Barton Smith In fluids measurements, the uncertainty of an instrument is typically fixed or a percentage of the measured value. One expects that the usually unknown true error in the measurement is within the 2-sigma uncertainty 95{\%} of the time. In the present work, the relevance and statistical properties of uncertainties are explored with PIV data but this equally applies to other measured quantities In PIV the measurement error is a function of several image and flow quantities that vary in time and space. Therefore the uncertainty also varies in time and space and is not necessarily a function of the measured velocity. This makes comparison of error and uncertainty much less straight forward. We present several statistical methods of comparing uncertainties with the true errors including coverage factors, histograms, profiles and 2D-plots to assess the quality of uncertainty quantification methods. It can be shown that for the simpler case of no bias errors, the standard deviation of the error should be compared to the standard deviation of the uncertainty. We also compare conditional averages according to seeding density or out-of-plane motion to validate the sensitivity of the methods to different error sources. Results are shown for recently developed PIV uncertainty methods. [Preview Abstract] |
Tuesday, November 25, 2014 1:44PM - 1:57PM |
R29.00004: Using Proper Orthogonal Decomposition and Dynamic Mode Decomposition for comparing CFD and experimental results in unsteady aerodynamics Amandine Guissart, Thomas Andrianne, Grigorios Dimitriadis, Vincent Terrapon Typically, the integration of Experimental Fluid Dynamics (EFD) and Computational Fluid Dynamics (CFD) allows a better understanding of the flow of interest by leveraging the complementary of their respective data. The comparison of computational and experimental results is an important but difficult step of this integration, particularly in the case of unsteady flows. This work presents a method for quantitative comparison of unsteady aerodynamic data using two decomposition methods: the Proper Orthogonal Decomposition (POD) and the Dynamic Mode Decomposition (DMD). It is applied to extract the dominant structures of the flow around a static and oscillating 4:1 rectangular cylinder. The experimental and numerical data are obtained through two-dimensional Time-resolved Particle Image Velocimetry (Tr-PIV) measurements and unsteady Reynolds-Averaged Navier-Stokes (uRANS) simulations, respectively. The results illustrate the complementarity of the two decomposition methods. It is also shown that this approach represents a powerful tool enabling the analysis and the quantitative comparison of the main spatial (POD) and temporal (DMD) characteristics of unsteady flows. [Preview Abstract] |
Tuesday, November 25, 2014 1:57PM - 2:10PM |
R29.00005: Characterizing and correcting for the effect of sensor noise in the dynamic mode decomposition Scott Dawson, Maziar Hemati, Matthew Williams, Clarence Rowley Dynamic mode decomposition (DMD) provides a powerful means of extracting insightful dynamical information from fluids datasets. Like any data processing technique, DMD's usefulness relies on its ability to extract real and accurate dynamical features from noise-corrupted data. Here we show analytically that sensor noise can bias the results (eigenvalues and modes) of the DMD algorithm. This bias can be accurately predicted, to the point that we may derive an analytic correction factor that facilitates its removal. We propose a number of additional modifications to the DMD algorithm that reduce or eliminate this bias, even when the noise characteristics are unknown. We demonstrate the performance of these modifications on a range of synthetic, numerical, and experimental datasets, and also compare and integrate our modified algorithms with other DMD variants proposed in recent literature. [Preview Abstract] |
Tuesday, November 25, 2014 2:10PM - 2:23PM |
R29.00006: Nano-scale measurements of dense particle-laden interface dynamics Craig Snoeyink, Gordon Christopher, Sourav Barman We discuss an image analysis algorithm that allows one to accurately locate in three dimensions individual fluorescent particles even when closely spaced. Traditionally, locating multiple closely spaced particles has been difficult as the overlapping particle images obscures relevant data. Current state-of-the-art algorithms have difficulty with more then 2-3 particles per micron square box when viewed with a 100x objective. We show that this algorithm, when implemented with the Bessel Beam Microscopy system, is capable of locating particles at an order of magnitude greater particle density and with nano-scale resolution in depth. The utility of this technique is demonstrated by measuring the dynamics of fluorescent particles on a particle laden oil-water interface with nano-scale resolution. The relative position and motion of these particles has a direct effect on the fluidic behavior of these interfaces. [Preview Abstract] |
Tuesday, November 25, 2014 2:23PM - 2:36PM |
R29.00007: 3D positional tracking of ellipsoidal particles in a microtube flow using holographic microscopy Hyeok Jun Byeon, Kyung Won Seo, Sang Joon Lee Understanding of micro-scale flow phenomena is getting large attention under advances in micro-scale measurement technologies. Especially, the dynamics of particles suspended in a fluid is essential in both scientific and industrial fields. Moreover, most particles handled in research and industrial fields have non-spherical shapes rather than a simple spherical shape. Under various flow conditions, these non-spherical particles exhibit unique dynamic behaviors. To analyze these dynamic behaviors in a fluid flow, 3D positional information of the particles should be measured accurately. In this study, digital holographic microscopy (DHM) is employed to measure the 3D positional information of non-spherical particles, which are fabricated by stretching spherical polystyrene particles. 3D motions of those particles are obtained by interpreting the holograms captured from particles. Ellipsoidal particles with known size and shape are observed to verify the performance of the DHM technique. In addition, 3D positions of particles in a microtube flow are traced. This DHM technique exhibits promising potential in the analysis of dynamic behaviors of non-spherical particles suspended in micro-scale fluid flows. [Preview Abstract] |
Tuesday, November 25, 2014 2:36PM - 2:49PM |
R29.00008: ABSTRACT WITHDRAWN |
Tuesday, November 25, 2014 2:49PM - 3:02PM |
R29.00009: Olive Oil Tracer Particle Size Analysis for Optical Flow Investigations in a Gas Medium Shaun Harris, Barton Smith Seed tracer particles must be large enough to scatter sufficient light while being sufficiently small to follow the flow. These requirements motivate a desire for control over the particle size. For gas measurements, it is common to use atomized oil droplets as tracer particles. A Laskin nozzle is a device for generating oil droplets in air by directing high-pressure air through small holes under an oil surface. The droplet diameter frequency distribution can be varied by altering the hole diameter, the number of holes, or the inlet pressure. We will present a systematic study of the effect of these three parameters on the resultant particle distribution as it leaves the Laskin nozzle. The study was repeated for cases where the particles moved through a typical jet facility before their size was measured. While the jet facility resulted in an elimination of larger particles, the average particle diameter could be varied by a factor of two at both the seeder exit and downstream of the jet facility. [Preview Abstract] |
Tuesday, November 25, 2014 3:02PM - 3:15PM |
R29.00010: MRI Based Diagnostics for Temperature Measurements in Turbulent Flows Lauren Sascha Burton, Christopher J. Elkins, John K. Eaton Accurate modeling of the thermal diffusion in the complex turbulent flows related to cooling high temperature gas turbine blades is critical to optimize the performance and predict the lifetime of the blades. Magnetic Resonance Imaging (MRI) techniques for temperature measurement in simple but related flows are being developed in an effort to obtain full field thermal measurements to better understand diffusion processes and support the development of more accurate computational models in these flows. Magnetic Resonance Thermometry (MRT) utilizes the temperature dependence of the hydrogen proton resonant frequency (PRF) in water. MRT is now routinely used to measure tissue temperatures during medical procedures, and a few previous studies have made velocity and temperature measurements in turbulent pipe flows. In this study, MRT is applied to the flow of a heated single hole film cooling jet (Reynolds number 3000) inclined at 30 degrees injected into a cold developing turbulent channel flow (Reynolds number 25,000 based on bulk velocity and channel height.) The jet fluid temperature is 30 degrees Celsius above the temperature in the channel. The temperature measurements compare well to previously published results for measured passive scalar concentration in the same flow although the temperature measurements show higher uncertainties of 5-10$\% $ of the temperature difference. Techniques for reducing this uncertainty will be presented as well as procedures for applying MRT to quantify the turbulent heat transfer coefficient in turbulent internal flows. [Preview Abstract] |
Tuesday, November 25, 2014 3:15PM - 3:28PM |
R29.00011: ABSTRACT WITHDRAWN |
Tuesday, November 25, 2014 3:28PM - 3:41PM |
R29.00012: Spatially-resolved, three-dimensional spray characterization of impinging jets by digital in-line holography Jian Gao, Neil Rodrigues, Paul Sojka, Jun Chen The impinging jet injector is a preferred method for the atomization of liquid rocket propellants. The majority of experimental studies in literature are not spatially-resolved due to the limitations of widely available point-wise and two-dimensional (2D) diagnostic techniques such as phase Doppler anemometry (PDA), which requires significant experimental repetitions to give spatially-resolved measurements. In the present study, digital in-line holography (DIH) is used to provide spatially-resolved, three-dimensional (3D) characteristics of impinging jet sprays. A double-exposure DIH setup is configured to measure droplet 3D, three-component velocity as well as the size distribution. The particle information is extracted by the hybrid method, which is recently proposed as a particle detection method. To enlarge the detection volume, two parallel, collimated laser beams are used to simultaneously probe the spray at two locations, and two identical cameras are used to record the corresponding holograms. Such a setup has a detection volume of approximately 20 cm by 3.6 cm by 4.8 cm. Sprays of both Newtonian and non-Newtonian liquids corresponding to regimes at relatively lower jet Reynolds and Weber numbers are investigated. Measurements from DIH are further verified by comparison with experimental data obtained from shadowgraph and PDA. It is revealed that DIH is particularly suitable to provide spatially-resolved, 3D measurements of impinging jet sprays that are not particularly dense. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700