Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session L21: Experimental Techniques: Pressure, Density, Temperature and Concentration |
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Chair: Michael Hargather, New Mexico Institute of Mining and Technology Room: Georgia World Congress Center B309 |
Monday, November 19, 2018 4:05PM - 4:18PM |
L21.00001: Schlieren and cross-schlieren imaging for quantitative flow visualization Nobuyuki Fujisawa, Koki Iwasaki, Keita Ozawa, Kei Fujisawa, Takayuki Yamagata The schlieren imaging is a fundamental flow visualization technique applicable to combustion flame and high-speed flows. In this talk, some applications of the schlieren imaging are shown to understand the flow physics. They include the flickering combustion flame under acoustic excitation, screech tone phenomenon from underexpanded supersonic jet and the shockwave formation in a cavitating jet. Furthermore, the development of the schlieren for quantitative flow visualization is examined by introducing the cross-schlieren imaging and the usefulness of this experimental technique is studied. |
Monday, November 19, 2018 4:18PM - 4:31PM |
L21.00002: Development of stereo schlieren image velocimetry Kyle J Benalil, Raj Bhakta, Michael John Hargather Schlieren and shadowgraph imaging have been used to quantify velocity field characteristics of jets in two dimensions, but no thorough study of the turbulence or three-dimensional motion using these techniques has been completed. This work explores the capabilities of tracking turbulent flow in three dimensions by combining the information from schlieren and shadowgraph imaging with a multi-camera stereo-imaging system. Schlieren and projective shadowgraph setups were used with two high-speed cameras at small stereo angles to develop three-dimensional reconstructions of refractive index fields. A two-dimensional helium jet study was performed with schlieren image velocimetry (SIV) to track turbulent structure motions. Particle image velocity was conducted with the helium jet to validate the three-dimensional SIV measurements. The study showed that stereo schlieren imaging with parallel-light lens systems did not yield a depth effect. However, the projective shadowgraphy experiment was able to reconstruct the helium jet into three-dimensional space because of the inherent diverging light rays. |
Monday, November 19, 2018 4:31PM - 4:44PM |
L21.00003: The Development and Application of Plenoptic Background Oriented Schlieren Imaging as a Flow Visualization Technique Jenna N Klemkowsky, Christopher J Clifford, Brian S Thurow, Brett Bathel Plenoptic background oriented schlieren imaging (plenoptic BOS) is a relatively new schlieren technique that acquires multiple line-of-sight measurements in a single snapshot, all of which can be collectively used to generate focused BOS images. Such images are used to qualitatively and quantitatively determine where density gradients are located in three-dimensional object space. This presentation will provide an overview of the plenoptic BOS technique and a brief review of recent applications and experiments using plenoptic BOS. Additionally, a discussion of future work will highlight upcoming experiments and the transition of this work towards reconstructing a three-dimensional density field using two camera plenoptic BOS.
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Monday, November 19, 2018 4:44PM - 4:57PM |
L21.00004: Development of synchrotron X-ray computed tomography for quantitative measurements of gas-phase temperature in reacting flows Emeric Boigne, Danyal Mohaddes Khorassani, Priyanka Muhunthan, Sadaf Sobhani, Dula Parkinson, Harold Barnard, Matthias Ihme Laboratory X-ray computed tomography systems have recently been used to measure the 3D temperature field in reacting flows. The present work extends this technique to micro-scale resolution by employing a synchrotron source. Of particular focus is hereby the quantification of the accuracy and uncertainties of the measurements and the examination of conditions required to retrieve the gas temperature from X-ray absorption measurements. The specific advantages and constraints of using a synchrotron source are discussed and the experimental procedure is detailed. Cold-flow calibration experiments as well as measurements on a flat-flame are reported. The merit of this measurement technique for micro-scale applications with optically inaccessible media is then illustrated in the context of a porous media burner. The 3D temperature field extracted from X-ray computed tomography measurements is examined to identify interstitial combustion modes and flame/wall coupling within the porous matrix. |
Monday, November 19, 2018 4:57PM - 5:10PM |
L21.00005: Towards Pressure Measurements Using Filtered Rayleigh Scattering David Feng, Benjamin M. Goldberg, Mikhail N. Shneider, Richard B. Miles Nonintrusive laser diagnostics are critical for the measurement of pressure, temperature, density, and velocity in a variety of aerospace and combustion applications. One of these diagnostics, filtered Rayleigh scattering (FRS), has been shown to be a useful in this regard. The primary advantage of FRS is that 1) it does not require particle seeding and 2) background scattering is strongly suppressed by the molecular vapor filter employed. Furthermore, the filter properties and collection angle can be adjusted such that the dependence on the thermal broadening of the Rayleigh scattering can be removed, thus making the signal proportional only to pressure via the ideal equation of state. We present a model of FRS for temperature insensitivity and pressure sensitivity with experimental results on the temperature insensitivity capabilities. Temperature insensitivity from 300-500 K is demonstrated in air, and a reduction in temperature sensitivity is demonstrated for a Hencken methane/air flame at ~1800 K by changing the observational angle and filter vapor pressure. Modelling of pressure shows that the pressure dependence of the FRS signal remains linear in these regimes. |
Monday, November 19, 2018 5:10PM - 5:23PM |
L21.00006: Local temperature and composition measurements in pressurised CH4/air flames with LIGS (Laser Induced Grating Spectroscopy) Francesca De Domenico, Thibault F. Guiberti, Simone Hochgreb, William R. Roberts, Gaetano Magnotti Laser Induced Grating Spectroscopy (LIGS) -a seedless non intrusive point measurement technique- is applied in non-sooty laminar flat flames to determine temperature and water concentration. A 1064 nm pulsed seeded laser is used as pump laser. When sufficiently high energy is delivered by the pulses (around 100 mJ), the weak rotational transition of the water molecules in the probe volume is excited (thermalisation) and the electric field of the interference structure polarizes the dielectric medium (electrostriction). The LIGS signal is then probed with a CW laser at 532 nm. We demonstrate that the ratio between the electrostriction and the thermalisation peaks in the signals is an indicator of the water concentration, which is used to determine the gas composition. The speed of sound is extracted from the oscillation frequency of the signals from their FFTs. Once the composition is known, the temperature is determined with an iterative process. Temperature and composition data compare favourably with thermocouple measurements and flame simulations. A pressurised environment is needed to enhance the signal and obtain a sufficient number of peaks to enable a Fourier transform. These results confirm the potential for LIGS-based thermometry for high-precision combustion processes. |
Monday, November 19, 2018 5:23PM - 5:36PM |
L21.00007: Experimental Investigations of Airborne Odor Plumes Erin G. Connor, John P. Crimaldi We quantify the concentration distribution of airborne scalar plumes using planar laser-induced fluorescence. An ultraviolet laser excites fluorescence from an isokinetic release of acetone vapor (Sc≈1.5) in a benchtop-scale low-speed wind tunnel. Neutral buoyancy of the tracer gas is achieved by blending a mixture of helium and air, via mass flow controllers. We image the fluorescence at 15 Hz. Using this technique, we collect spatiotemporal concentration data with a detectability limit of 0.5% of the source concentration, and a field of view measuring 16 cm by 30 cm. We quantify plumes for several release configurations which exhibit different characteristics when comparing spatial distributions of instantaneous concentration, mean concentration, root-mean-square fluctuations, and concentration intermittency. The principal motivation is to further our understanding of the information available to terrestrial animals while navigating within odor plumes. The experiments provide novel data of airborne odor plumes that are then used in a range of related studies of animal olfactory navigation. We conclude by discussing approaches to advance these related studies. |
Monday, November 19, 2018 5:36PM - 5:49PM |
L21.00008: Progress in molecular based thermometry and velocimetry for the ZBOT experiment Shahram Pouya, David A Olson, Gary Blanchard, Manoochehr M Koochesfahani We report on our progress in the development of whole-field molecular based optical techniques for velocimetry and thermometry in the NASA Zero Boil-off Tank (ZBOT) experiment. ZBOT is a small-scale experiment aimed at study of heat transfer and phase change of cryogenic fluids under microgravity condition. The experiment on the International Space Station uses a transparent simulant fluid, Perfluoropentane (PnP), a saturated fluorocarbon with unique physical properties that make application of optical diagnostic methods challenging. We present the feasibility of molecular tagging velocimetry (MTV) and Laser Induced Fluorescence (LIF) thermometry in PnP medium. Results of single component velocimetry and planar thermometry are shown in a simple ground test experiment involving the discharge of a hot/cold PnP jet into ambient PnP fluid. |
Monday, November 19, 2018 5:49PM - 6:02PM |
L21.00009: Surface pressure measurements of an impinging jet with deflectometry Rene Kaufmann, Bharathram Ganapathisubramani, Fabrice Pierron Optical measurements were used to reconstruct low amplitude surface pressure fluctuations in high resolution on a thin plate with the Virtual Fields Method (VFM). Surface slopes induced by an impinging synthetic jet were measured contactless using a highly sensitive deflectometry setup. The periodic slope signals, which were below instantaneous noise level, were recovered using phase averaging. Time filter techniques were used with equal success, obtaining slope maps with amplitudes well below 10 mm km-1. Based on the Principle of Virtual Work, the VFM allowed reconstructions of surface pressure from full-field data. It requires knowledge of the plate material parameters, surface curvatures and accelerations as well as a set of virtual fields to be chosen. Curvatures were calculated from the measured surface slopes. Accelerations were found to be negligible here based on LDV measurements. Virtual fields were defined piecewise using Hermite 16 shape functions. Sensitivity analysis allowed assessing the systematic error. Results were validated using pressure transducer measurements. The outcome is remarkable with reconstructed pressure amplitudes of down to only several Pa of flow structures of the size of few mm in high resolution. |
Monday, November 19, 2018 6:02PM - 6:15PM |
L21.00010: Data recovery of clean signal from highly noisy data: a compressed data fusion approach Xin Wen, Yingzheng Liu, Wenwu Zhou, Di Peng Compressed sensing algorithm is used to fuse spatially resolved but noisy full-field data with clean but scattered data to reconstruct full-field clean data. In the applications of flow measurement, control, and monitoring, a particularly challenging task is to recover clean signal from highly noisy data. One commonly used method is low dimensional analysis. For example, proper orthogonal decomposition (POD) is commonly used to extract coherent signal patterns from noisy data. However, with a low signal-to-noise ratio, the selection criteria of the proper POD modes for reconstruction is usually based on subjective observation. In addition, the strong noise can severely distort the mode coefficients. Therefore, POD analysis not only has restriction in the applications of complicated flow phenomena, but also can lead to a low-quality reconstruction. In current method, the two problems are naturally solved by compressed sensing, which is to find the optimal mode coefficients to reconstruct the clean data using the most relevant POD modes. Fabricated patterns and fast PSP measurement pressure fields of wake flows are tested. It shows that current compressed data fusion approach can significantly improve the performance of recovery clean data compared with POD analysis. |
Monday, November 19, 2018 6:15PM - 6:28PM |
L21.00011: Quantifying the quality of unsteady pressure reconstructed from remotely measured pressure signals John W Strike, Pourya Nikoueeyan, Michael Hind, Manjinder Singh, Jonathan W Naughton Remotely measured pressure systems using tap/tubing geometries are robust and flexible but are limited in frequency response due to the signal distortion induced by the tubing between the tap and the pressure transducer. Many users typically use tap/tubing pressure systems for steady state measurements or dynamic measurements at low frequencies. Analytical system response models that account for the physical system have been used to extend the frequency response of the remotely measured systems. However, noise in the measurement system and inaccurate estimates of the analytical system response model leads to inaccuracies in the reconstructed pressure. A dynamic pressure calibration process is required to quantify these uncertainties. Furthermore, the bandwidth and quality of the reconstruction are dependent on the input signal characteristics, the accuracy of the analytical model, and the ability to minimize aliasing of signal noise in the reconstruction. Tools developed to provide high frequency dynamic calibrations for a wide variation of tubing geometries are presented, and the effect of noise minimization and parameter sensitivity on the reconstructed signal is discussed. |
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