Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session H14: General Experiments III |
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Chair: Jun Chen, Purdue University Room: 27B |
Monday, November 19, 2012 10:30AM - 10:43AM |
H14.00001: Validity of Molecular Tagging Velocimetry in a Cavitating Flow for Turbopump Analysis Kayla Kuzmich, Doug Bohl This research establishes multi-phase molecular tagging velocimetry (MTV) use and explores its limitations. The flow conditions and geometry in the inducer of an upper stage liquid Oxygen (LOX)/LH2 engine frequently cause cavitation which decreases turbopump performance. Complications arise in performing experiments in liquid hydrogen and oxygen due to high costs, high pressures, extremely low fluid temperatures, the presence of cavitation, and associated safety risks. Due to the complex geometry and hazardous nature of the fluids, a simplified throat geometry with water as a simulant fluid is used. Flow characteristics are measured using MTV, a noninvasive flow diagnostic technique. MTV is found to be an applicable tool in cases of low cavitation. Highly cavitating flows reflect and scatter most of the laser beam disallowing penetration into the cavitation cloud. However, data can be obtained in high cavitation cases near the cloud boundary layer. Distribution A: Public Release, Public Affairs Clearance Number: 12654 [Preview Abstract] |
Monday, November 19, 2012 10:43AM - 10:56AM |
H14.00002: An Approach for Correcting the Velocity Bias Error in One-Component Molecular Tagging Velocimetry: Theoretical Analysis Ahmed Naguib, Patrick Hammer, Shahram Pouya, Manoochehr Koochesfahani One-component Molecular Tagging Velocimetry (1c-MTV) using line tagging has the advantage of providing velocity information with very high spatial resolution: at every pixel along the imaged line of tagged molecules. This renders the technique particularly suitable for near-wall, boundary-layer-resolved measurements. However, a non-negligible bias error could affect the measurements if the velocity component along the ``tag line'' is substantial relative to the measured component and/or when the time delay between image pairs is large. In this presentation, which is the first of a sequence of two talks, a theoretical analysis is detailed for expressing this bias error in a Taylor-series framework. The error estimate based on this analysis is validated using simple flows with known analytical solutions. Moreover, by truncating the Taylor-series expansion at a low order, it is possible to use the resulting form as basis for a practical method for linear, or higher-order, correction of the bias error. Experimental demonstration of the viability of the method will be presented in a follow-up talk. [Preview Abstract] |
Monday, November 19, 2012 10:56AM - 11:09AM |
H14.00003: An Approach for Correcting the Velocity Bias Error in One-Component Molecular Tagging Velocimetry: Experimental Demonstration Patrick Hammer, Shahram Pouya, Ahmed Naguib, Manoochehr Koochesfahani Measurements and simulated experiments have been performed to demonstrate the validity of a method to correct for the velocity bias error associated with single-component Molecular Tagging Velocimetry due to the presence of a velocity component along the line of tagged molecules. The method, the theoretical basis for which is presented in a preceding talk, utilizes two MTV images obtained using two different time delays relative to the un-delayed image to correct for the bias error. An experiment based on fully developed flow in a rectangular channel is used to validate the correction approach. In the experiment, a velocity component along the ``tag line'' is deliberately imposed by tagging molecules along a line that is inclined to the flow direction in the channel. The error produced by interrogation normal to the line is corrected using the new approach, and the result is compared against bias-error-free measurements based on interrogation of the line in the flow direction. The results show that the new approach successfully corrects for the bias error. The sensitivity of the correction to parameters such as measurement noise, time-delay pairs, and flow angle, is assessed using simulated experiments. [Preview Abstract] |
Monday, November 19, 2012 11:09AM - 11:22AM |
H14.00004: Error Reduction in Molecular Tagging Velocimetry (MTV) Processing Using Image Filtering Doug Bohl, Mike Caso Prior work has shown that the error level in MTV measurements is closely tied to the image Signal to Noise (SN) level. In practice the SN ratio will depend on experimental conditions such as attenuation, Field of View, laser power, camera, etc.; however, there is a minimum SN level that can be achieved for any given experiment. Experience has shown that MTV images typically have a SN=2-8. It is therefore desirable to be able to lower image noise after the images are acquired to reduce measurement error. In this work post processing MTV images using standard image filtering schemes such as Gaussian Blur, FFT (band pass), median filtering etc. were investigated. Past results on synthetic images showed that for very noisy images (i.e. SN$<$4) all filtering techniques improved the displacement error by 10-40{\%}. As the SN increased filtering because less effective in decreasing error and in some cases increased the measurement error. The current work investigates the effect of image filtering on experimental images and compares those results to the synthetic image study. [Preview Abstract] |
Monday, November 19, 2012 11:22AM - 11:35AM |
H14.00005: Voltage-Current Characteristics of Plasma Pressure Sensor Eric Matlis, Thomas Corke, Curtis Marshall, Sivaram Gogineni A pressure sensor based on the use of plasma as the sensing element is being developed. This is an AC-driven, continuous-wave plasma which is encapsulated between two metallic bare electrodes with a small air gap on the order of 0.03 mm. The sensor uses a non-equilibrium discharge at less than 20 Watts of power. This devices features an amplitude modulated carrier to measure both mean and dynamic pressure. The frequency response is limited only by the carrier frequency which can be as high as 1 MHz. Glow-to-Arc transition is controlled with the use of a capacitive and resistive circuit in series with the discharge. A pressure chamber is used to document the plasma power characteristics as the ambient pressure is controlled from atmospheric to 100 psi. Plasma power is controlled so as to maintain the plasma in the normal and abnormal glow regimes. The phase angle between voltage and current is recorded as a function of pressure. This analysis will aid in the development of a feedback control and calibration of the pressure sensor. [Preview Abstract] |
Monday, November 19, 2012 11:35AM - 11:48AM |
H14.00006: Global Pressure Measurement of Unsteady-State Flow and Motion on Fluttering Airfoil Taika Okabe, Takeshi Miyazaki, Kenichi Saitoh, Hirotaka Sakaue Pressure-sensitive paint (PSP) measurement has been applied to a fluid dynamic measurement. It can be applied to a steady-state flow in the transonic and supersonic wind tunnels. To extend the PSP measurement, an unsteady-state measurement is paid attention. It can be categorized by the unsteady-state flow and unsteady motion of the PSP-coated model. The former can be captured by using a porous PSP. The fastest PSP gives the response time on the order of ten microseconds. For the latter, the motion-capturing PSP method is studied to capture the unsteady motion. It consists of a two-color PSP and color camera. One color corresponds to the pressure-independent luminescence, and the other to the pressure-dependent luminescence. The former is used to cancel the pressure-independent distribution of a pressure-dependent image. The two-color images are simultaneously captured by the color camera. A combination of the unsteady-state flow and the motion can be occurred for an unsteady-state measurement. We present one of the cases, which is a flutter on an airfoil. By combining a porous PSP and the motion-capturing method, a pressure distribution on a fluttering airfoil (2-D YXX 30{\%} span) is captured. [Preview Abstract] |
Monday, November 19, 2012 11:48AM - 12:01PM |
H14.00007: Performance of an untethered micro-optical pressure sensor Tindaro Ioppolo, Maurizio Manzo, Paul Krueger We present analytical and computational studies of the performance of a novel untethered micro-optical pressure sensor for fluid dynamics measurements. In particular, resolution and dynamic range will be presented. The sensor concept is based on the whispering galley mode (WGM) shifts that are observed in micro-scale dielectric optical cavities. A micro-spherical optical cavity (liquid or solid) is embedded in a thin polymeric sheet. The applied external pressure perturbs the morphology of the optical cavity leading to a shift in its optical resonances. The optical sensors are interrogated remotely, by embedding quantum dots or fluorescent dye in the micro-optical cavity. This allows a free space coupling of excitation and monitoring of the optical modes without the need of optical fibers or other cabling. With appropriate excitation and monitoring equipment, the micro-scale sensors can be distributed over a surface (e.g., including flexible biological surfaces) to monitor the local pressure field. [Preview Abstract] |
Monday, November 19, 2012 12:01PM - 12:14PM |
H14.00008: Simultaneous measurement of morphological shape and 3D motion of objects using digital holographic microscopy Kyung Won Seo, Sang Joon Lee The phase-imaging technique using off-axis holography and the volumetric measurement of particle fields using in-line holography have been investigated separately. In the present study, we combine the advantages of these two techniques. A high-speed off-axis holographic system is established to simultaneously measure the morphology and the 3D motion of particles in a microtube flow with high spatial and temporal resolutions. The off-axis holography setup with transmission-type configuration is based on the principle of Mach--Zehnder interferometry. Off-axis holograms were numerically reconstructed in amplitude and phase, after frequency-domain filtering by adopting the angular spectrum method. The amplitude information of the reconstructed image indicates the 3D positions of the suspended particles, and phase information provides the object morphology or physical thickness. As a result, the 3D trajectories, instantaneous velocity, and the 3D shape of particles are extracted through a position detection and particle tracking velocimetry (PTV) algorithm and quantitative phase map. This holographic microscopy technique demonstrates the feasibility of the simultaneous measurement of the 3D dynamic behavior and temporal shape of objects. [Preview Abstract] |
Monday, November 19, 2012 12:14PM - 12:27PM |
H14.00009: Automatic characterization of particle fields using digital holography Jian Gao, Jun Chen, Daniel Guildenbecher, Phillip Reu An automatic algorithm is developed to characterize sizes and 3D positions of particle fields using digital holography. The reconstructed intensity image is used in conjunction with the edge sharpness of the particle image to automatically determine the level for thresholding of the intensity image. The morphology and transverse position of an individual particle are extracted from the binary image while its axial position is decided by maximizing the edge sharpness of the particle along the axial direction. A comparison using synthetic holograms with published particle detection approaches demonstrates the superiority of the proposed method. We further apply the method to segment a reconstructed image of a particle field. In particular, measurement errors introduced by transversely overlapped particles in dense particle fields are eliminated using a particle refinement algorithm based on 3D segmentation. The results demonstrate significant improvements in both the size and position measurements. The new method is applied to processing of experimental holograms of a particle field to further demonstrate its effectiveness. [Preview Abstract] |
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