Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session H14: Experimental Techniques V: Two-Phase/Ablation |
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Chair: Douglas G. Bohl, Clarkson University Room: 302 |
Monday, November 25, 2013 10:30AM - 10:43AM |
H14.00001: Comparison of Global Sizing Velocimetry and Phase Doppler Anemometry measurements of alternative jet fuel sprays Reza Sadr, Kumaran Kannaiyan Atomization plays a crucial precursor role in liquid fuel combustion that directly affects the evaporation, mixing, and emission levels. Laser diagnostic techniques are often used to study the spray characteristics of liquid fuels. The objective of this work is to compare the spray measurements of Gas-to Liquid (GTL) jet fuels obtained using Global Sizing Velocimetry (GSV) and Phase Doppler Anemometry (PDA) techniques at global and local levels, respectively. The chemical and physical properties of GTL fuels are different from conventional jet fuels, owing to the difference in their production methodology. In this work, the experimental facility, the measurement techniques, and spray characteristics of two different GTL fuels are discussed and compared with those of Jet A-1 fuel. Results clearly demonstrate that although the global measurement gives an overall picture of the spray, fine details are obtained only through local measurements and complement in gaining more inferences into the spray characteristics. The results also show a close similarity in spray characteristics between GTL and Jet A-1 fuels. [Preview Abstract] |
Monday, November 25, 2013 10:43AM - 10:56AM |
H14.00002: Dark Field Imaging of Multiphase Fluid Flows Barry Scharfman, Alexandra Techet A novel method has been developed for spatially and temporally resolving three-dimensional multiphase fluid flows. Image volumes are captured using a multiple CCD sensor array consisting of a planar array of cameras. This is similar to light field imaging, but no light enters the cameras directly; rather, lights surround the scene and a dark sheet is placed directly across from the array. Therefore, each camera records an essentially binary image of the scene from a different angle, which simplifies subsequent image processing. Synthetic aperture refocusing techniques are applied to the raw camera array images, each with large depths of field, to obtain a stack of post-processed images, with narrow depth of field, where each image in the stack is located on a specific focal plane. Then, flow features are extracted from the binary refocused volume, allowing the scene to be reconstructed in three dimensions over time. Simulations and experimental fluid flows are used to validate and improve this technique. [Preview Abstract] |
Monday, November 25, 2013 10:56AM - 11:09AM |
H14.00003: Naphthalene Planar Laser-Induced Fluorescence Imaging of Orion Multi-Purpose Crew Vehicle Heat Shield Ablation Products Christopher S. Combs, Noel T. Clemens, Paul M. Danehy The Orion Multi-Purpose Crew Vehicle (MPCV) calls for an ablative heat shield. In order to better design this heat shield and others that will undergo planetary entry, an improved understanding of the ablation process is required. Given that ablation is a multi-physics process involving heat and mass transfer, codes aiming to predict heat shield ablation are in need of experimental data pertaining to the turbulent transport of ablation products for validation. At The University of Texas at Austin, a technique is being developed that uses planar laser-induced fluorescence (PLIF) of a low-temperature sublimating ablator (naphthalene) to visualize the transport of ablation products in a supersonic flow. Since ablation at reentry temperatures can be difficult to recreate in a laboratory setting it is desirable to create a limited physics problem and simulate the ablation process at relatively low temperature conditions using naphthalene. A scaled Orion MPCV model with a solid naphthalene heat shield has been tested in a Mach 5 wind tunnel at various angles of attack in the current work. PLIF images have shown high concentrations of scalar in the capsule wake region, intermittent turbulent structures on the heat shield surface, and interesting details of the capsule shear layer structure. [Preview Abstract] |
Monday, November 25, 2013 11:09AM - 11:22AM |
H14.00004: Optimization of Chemical Concentrations for Molecular Tagging Velocimetry Wyatt Spellman, Douglas Bohl Molecular Tagging Velocimetry (MTV) is a whole field optical diagnostic technique where long lived chemical tracers are mixed on a molecular level with the working fluid. The chemical tracer is excited into phosphorescence using a light source, typically a pulsed UV laser. Because MTV is an absorption/emission technique, versus PIV which is a scattering technique, the light levels can be an order of magnitude lower than that for PIV. It is therefore important to optimize the individual chemical concentrations to maximize the emission in the desired field of view. Three chemicals are used in combination to create the molecular tracer in water. As with all absorption techniques, the intensity of the emitted light is a function of the depth of penetration (i.e. the distance the light beam travels through the fluid medium) due to attenuation of the beam. Attenuation is a function of the tracer concentration, which for MTV is a complicated due to the use of three chemical to create the tracer chemical. In this work we investigate the effect of chemical concentration on the attenuation in order to optimize the mixture so that the emission levels are maximized at any specified depth in the fluid. [Preview Abstract] |
Monday, November 25, 2013 11:22AM - 11:35AM |
H14.00005: Adsorption of diatoms at the oil-water interface Niloofar Fathollahi, Jian Sheng Statistically robust experimental observations on 3D trajectory of diatoms approaching an oil-water interface is crucial for understanding sorption mechanisms of active particles, and interfacial rheology with over-arching implications in interfacial dynamics, droplet break and coalescence. Digital Holographic Cinematography is utilized to measure 3-D trajectories of diatoms, \textit{Thalassiosira pseudomona} and \textit{T. weissflogii} and simultaneously track the interface. Experiments are conducted in a 300x100x100mm chamber containing 32 ppt artificial seawater. A stationary pendant drop is created on the tip of a needle located at the center of the chamber. Three oil samples, Louisiana crude, hexadecane, and mineral oil, are used. Diatoms are injected at a height above the drop with a negligible velocity, where Diatom precipitates freely on its excess weight. Holograms of diatom and drop are recorded at 5 fps with a magnification of 1.3X and are streamed in real time allowing for long-term study of sorption onto a slowly aging interface. A novel autofocus algorithm enables us to determine 3D locations within an uncertainty of 0.05 particle diameter. This allows us to perform super-resolution measurement to determine the effects of location and orientation of diatoms on the adsorption rate at the oil-water interface. Funded by GoMRI. [Preview Abstract] |
Monday, November 25, 2013 11:35AM - 11:48AM |
H14.00006: Dynamics of particle---turbulence interaction at the dissipative scales Humberto Bocanegra Evans, Nico Dam, Willem van de Water We present results of a novel phosphorescent tagging technique that is particularly suited to study particle-laden flows. Using phosphorescent droplets we probe the dynamics of particle--turbulence interaction at the dissipative length scales. We create a cloud of droplets within a chamber capable of generating homogeneous, isotropic turbulence with zero-mean flow. The droplets have Stokes number St$\:\sim 1$, and the flow is intensely turbulent, with Reynolds number Re$_\lambda\:\approx 500$. Using a frequency-tripled Nd:YAG laser, we can tag a variety of volumes, such as thin slabs or thin, pencil-like cylinders. The droplets in these volumes glow during a few Kolmogorov times. By tracking the fate of pencil-shaped clouds using a fast (5 kHz) camera, we come to the surprising conclusion that they disperse faster than fluid elements, with a spreading rate reaching a maximum at ${\rm St} \approx 2$. Sheets of tagged droplets display preferential concentration at work; we discuss statistical quantities that can capture these events. [Preview Abstract] |
Monday, November 25, 2013 11:48AM - 12:01PM |
H14.00007: Wall Shear Stress in Oscillating Channel Flow Using Particle Image Velocimetry Blake Lance, Jesse Roberts, Barton Smith, Sean Kearney Offshore wind and water power are renewable sources with the potential for significant power generation. But each generation mechanism has risks from ocean floor structures that can disrupt natural sediment transport by increasing local shear stress. The Sediment Erosion Actuated by Wave Oscillations and Linear Flow (SEAWOLF) flume was designed and built to replicate wave motion with both oscillatory and unidirectional components to study sediment transport. The rectangular test section provides optical access for Particle Image Velocimetry (PIV) measurements. Additionally series of pressure taps allow for differential pressure measurements. Sine-wave oscillations and unidirectional flow in more than a dozen combinations are measured and presented. Phase locked measurements of volume flow rates, velocity fields, and pressure are acquired over several hundred cycles and phase averaged. High spatial resolution PIV is used near the wall for direct shear stress measurements. Since the flow is unsteady, the pressure drop in the test section has both inertial and friction contributions. To isolate the friction term, the pressure resulting from the fluid acceleration is subtracted. The synced PIV and pressure measurements on smooth walls where the viscous sublayer is formed confirm the accuracy of this method. The pressure sensor then measures shear stress on rough walls where the viscous sublayer is disrupted or non-existent and where optical access is difficult. [Preview Abstract] |
Monday, November 25, 2013 12:01PM - 12:14PM |
H14.00008: The gas generation measurement at high electric filed in electrokinetic devices Mena Tawfik, Thomas Hansen, Francisco J. Diez In generating high EO flows, a limiting factor is faradaic reactions which appear at high electric fields. The gas released at the electrodes due to the faradic reaction forms bubbles which blocks the flow direction and increase the system resistance. To understand the factors that affect the bubble generated and its effect on the flow at high electric field, the gas generated is measured experimentally. Both DC and asymmetric bipolar rectangular voltage waveform are used to control the gas generated volume. Comparing the gas generated measured experimentally with that calculated theoretically, we found that the results have the same trend with about 50\% gas generation efficiency. The gas generated volume is the same either applying DC or bipolar rectangular voltage waveform, however, it noticed that in the case of the bipolar rectangular voltage waveform due to the continuously switch of the flow direction, the bubble is detached early from the electrodes that leads to smaller bubbles formation compared to the DC voltage. The effect of the frequency of the bipolar rectangular voltage waveform is to reduce the gas generation by about 15\% at high frequency $>$50 kHz. To the best of our knowledge this is the first time the gas generated was measured in electrokinetic devices. [Preview Abstract] |
Monday, November 25, 2013 12:14PM - 12:27PM |
H14.00009: Mechanisms and methods for biofouling prevention via aeration Natasha Dickenson, Charles Henoch, Jesse Belden Biofouling is a major problem for the Navy and marine industries, with significant economic and ecological consequences. Specifically, biofouling on immersed hull surfaces generates increased drag and thus requires increased fuel consumption to maintain speed. Considerable effort has been spent developing techniques to prevent and control biofouling, but with limited success. Control methods that have proven to be effective are costly, time consuming, or negatively affect the environment. Recently, aeration via bubble injection along submerged surfaces has been shown to achieve long-lasting antifouling effects, and is the only effective non-toxic method available [1,2]. An understanding of the basic mechanisms by which bubble-induced flow impedes biofouling is lacking, but is essential for the design of large-scale systems. We present results from an experimental investigation of several bubble induced flow fields over an inclined plate with simultaneous measurements of the fluid velocity and bubble characteristics using Digital article Image Velocimetry and high speed digital video. Trajectories of representative larval organisms are also resolved and linked with the flow field measurements to determine the mechanisms responsible for biofouling prevention. \\[4pt] [1] Scardino et al. 2009. \textit{J Mar Sci Technol.} No. A13. pp.3-10.\\[0pt] [2] Bullard et al. 2010. \textit{Aquatic Invasions}. 26: 587-593. [Preview Abstract] |
Monday, November 25, 2013 12:27PM - 12:40PM |
H14.00010: Optical sensor for detection of supercavity-body contact location Jesse Belden, Michael Jandron, Tadd Truscott Supercavitating vehicles have been the subject of intense research due to the potential for drag reduction and/or increased speeds. The control of such vehicles depends on accurate knowledge of planing forces generated by partial, transient wetting of afterbody surfaces. Measurement of the supercavity-body contact location, which determines the planing area, is thus critical for vehicle control. A robust sensor capable of measuring supercavity contact location along the length of a body is presented. The sensor operates on the optical principle of total internal reflection to differentiate between liquid and gas phases in contact with the body. An array of photodetectors is used to sense the presence or absence of light from a laser source to map the contact location. The theoretical operation and limitations of the sensor are discussed and several experiments are presented to validate the theory. Also, we present an elegant signal processing method to compensate for \textit{in situ} changes in ambient light conditions. [Preview Abstract] |
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