The Experts below are selected from a list of 8691 Experts worldwide ranked by ideXlab platform
A. J. Taylor - One of the best experts on this subject based on the ideXlab platform.
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Electromagnetically‐Driven Cylindrical 2‐D Shockwave Profile Measurements in Water with Laser Shadowgraphy
AIP Conference Proceedings, 2004Co-Authors: George Rodriguez, J.p. Roberts, A. J. TaylorAbstract:Experiments performed at the Los Alamos National Laboratory’s Atlas 23 MJ z‐pinch capacitor bank facility allows for experimental characterization of electro‐magnetically driven cylindrical shockwave implosions. Time resolved laser Shadowgraphy is used to dynamically image an Atlas generated liner‐target radial shock implosion in water with 2‐D imaging detail that provides benchmark results for numerical hydro‐code validation efforts at Los Alamos. Theoretical interest in these shock experiments arises since the shock propagation velocity is modified as shock‐strengthening effects are predicted to occur as material flow approaches the region of on‐axis convergence. Our laser Shadowgraph measurements capture eight separate image frames of shockwave motion in the water with an overall spatial and temporal resolution of ±0.25 mm and 10 ns, respectively. Imaging of the shockwave radial shape and position inside the water volume allows for quantitative comparison with numerical simulations. A linear fit to the...
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laser Shadowgraph measurements of electromagnetically driven cylindrical shock wave implosions in water
Journal of Applied Physics, 2003Co-Authors: George Rodriguez, J.p. Roberts, J.a. Echave, A. J. TaylorAbstract:Experiments performed at the Los Alamos National Laboratory’s Atlas 23-MJ z-pinch capacitor bank facility allows for experimental characterization of electromagnetically-driven cylindrical shock-wave implosions. Time-resolved laser Shadowgraphy is used to dynamically image an Atlas-generated liner–target radial shock implosion in water with two-dimensional imaging detail that provides benchmark results for numerical hydrocode validation efforts at Los Alamos. Our laser Shadowgraph measurements capture eight separate image frames of shock-wave motion in the water, with overall spatial and temporal resolutions of ±0.25 mm and 10 ns, respectively. Imaging of the shock-wave radial shape and position inside the water volume allows for quantitative comparison with numerical simulations. A linear fit to the average radius one-dimensional shock-wave trajectory plot yields a shock speed in the water of 6.65 mm/μs, corresponding to a Mach-4 shock. Comparison of the measured shock-wave trajectory with the numerical ...
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high speed laser Shadowgraphy for electromagnetically driven cylindrical implosions
Review of Scientific Instruments, 2001Co-Authors: G. Rodriguez, J.p. Roberts, J.a. Echave, A. J. TaylorAbstract:A laser Shadowgraphy system for high-speed imaging of a convergent cylindrical shockwave generated by an electromagnetically driven solid density liner implosion in Lucite is described. The laser Shadowgraphy system utilizes an advanced high-energy, long-pulse, frequency-doubled Nd:YAG laser for target illumination and a fast framing camera for multiple frame imaging of the shockwave as it radially converges and transits the Lucite. The time window resolution is 10 ns as determined by the fastest exposure time capable with the camera. Two on-axis symmetric implosions and two off-axis asymmetric implosion experiments were fielded at the Air Force Research Laboratory’s Shiva Star 4.2 MJ capacitor bank z-pinch facility. For each experimental shot, the Shadowgraphy system captured several frames of Shadowgraph images as the shockwave moved through the Lucite. Analysis of the shockwave Shadowgraph image shapes is done by fitting each Shadowgraph image to a generic elliptical fit function and plotting the resultant two-dimensional image fits for comparison. For the on-axis symmetric implosion shots, a radial trajectory plot is extracted and a radial shock velocity is calculated. The Lucite shock speed is seen to increase monotonically from an initial velocity of 7.9 mm/μs to a near final velocity of 13.4 mm/μs as convergence effects dominate the shock speed calculated at small radii.
Mohamad Metghalchi - One of the best experts on this subject based on the ideXlab platform.
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A mathematical model for Schlieren and Shadowgraph images of transient expanding spherical thin flames
Journal of Engineering for Gas Turbines and Power, 2004Co-Authors: Farzan Parsinejad, Matyas Matlo, Mohamad MetghalchiAbstract:Optical behavior of spherical flames is investigated using both Schlieren and Shadowgraph methods. A mathematical model has been developed to predict the intensity of refracted light beams interacting with a transient expanding thin flame. Experimental facilities have been built to visualize transient expanding spherical flames. The facilities include a cylindrical chamber with two end glasses for optical observation. Shadowgraph and Schlieren pictures of flame propagation have been taken using a high-speed charged coupled device camera. Experimental results are in very good agreement with those predicted by the theoretical model. Schlieren and Shadowgraph techniques have also been used to view smooth, cracked and cellular flames; these techniques will be useful in future in studies to determine the stability of propagating flame.
Christian Willert - One of the best experts on this subject based on the ideXlab platform.
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Experimental investigation of the transonic flow around the leading edge of an eroded fan airfoil
Experiments in Fluids, 2014Co-Authors: Joachim Klinner, Alexander Hergt, Christian WillertAbstract:The influence of leading edge modification on the time-averaged and instantaneous flow around a fan airfoil is investigated by particle image velocimetry (PIV), schlieren imaging and high-speed shock Shadowgraphs in a transonic cascade windtunnel. In addition to a global characterization of the time-averaged flow using PIV, the instantaneous passage shock position was extracted from single-shot PIV measurements by matching the tracer velocity across the normal shock with an exponential fit. The instantaneous shock positions are assigned to a probability density distribution in order to obtain the average position and the range of fluctuations of the eroded and reference leading edge. The profiles are used to estimate the response time of the particles to the normal shock which was found to be in the sub-microsecond range. Averaged PIV measurements and the probability density of shock position from both geometries are obtained at near stall and choked conditions. In order to extract the frequency range of the shock motion, the shadow of the shock wave was tracked using high-speed Shadowgraphy. The paper also provides details on the experimental implementation such as a specifically designed light-sheet probe.
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Tomographic Shadowgraphy for three-dimensional reconstruction of instantaneous spray distributions
Experiments in Fluids, 2012Co-Authors: Joachim Klinner, Christian WillertAbstract:Tomographic Shadowgraphy is an image-based optical technique capable of reconstructing the three dimensional instantaneous spray distributions within a given volume. The method is based on a multiple view imaging setup with inline illumination provided by current-pulsed LEDs, which results in droplet shadows being projected onto multiple sensor planes. Each camera records image pairs with short inter-framing times that allow the trajectories of the individual droplets to be estimated using conventional three-dimensional particle tracking approaches. The observed volume is calibrated with a traversed micro-target. A comparison is made between several photogrammetric and polynomial least-square camera calibration techniques regarding their accuracy in deep volume calibration at magnifications close to unity. A calibration method based on volume calibration from multiple planar homographies at equally spaced z -planes was found to produce the most reliable calibration. The combination of back-projected images at each voxel plane efficiently reproduces the droplet positions in three-dimensional space by line-of-sight (LOS) intensity reconstruction. Further improvement of the reconstruction can be achieved by iterative tomographic reconstruction, namely simultaneous multiplicative algebraic reconstruction technique (SMART). The quality of spray reconstruction is investigated using experimental data from multiple view Shadowgraphs of hollow cone and flat fan water sprays. The investigations are further substantiated with simulations using synthetic data.
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Tomographic Spray Shadowgraphy - A Feasibility Study
2011Co-Authors: Joachim Klinner, Christian WillertAbstract:This contribution introduces tomographic Shadowgraphy, a volume resolving imaging technique which is capable of recovering the liquid phase of a spray both spatially and temporally. The method is based on a multiple view camera setup with inline illumination provided by current pulsed LEDs which results in droplet shadows being projected onto the sensor plane. Each camera records image pairs with short interframing times which allows the trajectories of the individual droplets to be estimated using conventional three-dimensional particle tracking approaches. The observed volume is calibrated with a traversed micro target. A comparison is made between several photogrammetric and polynomial least square camera calibration techniques regarding their accuracy in deep volume calibration at magnifications close to unity. A calibration method based on volume calibration from multiple planar homographies at equally spaced z-planes was found to produce the most reliable calibration. Sequential combination of back-projected images at each voxel plane efficiently reproduces the droplet positions in three-dimensional space. The quality of spray reconstruction is investigated using experimental data from multiple view Shadowgraphs of a hollow cone spray.
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Tomographic Shadowgraphy for spray diagnostics
2011Co-Authors: Joachim Klinner, Christian WillertAbstract:This contribution introduces 3-D Shadowgraphy which is capable of resolving the placement of the liquid phase within a certain spray volume both spatially and temporally. The method is based on a multiple view camera setup and inline illumination provided by current pulsed LEDs. The quality of spray reconstruction was investigated using experimental data from multiple view Shadowgraphs of hollow cone and flat fan water sprays. After calibration and determination of a 3-D mapping function for each view a line-of-sight (LOS) intensity reconstruction was implemented. After sequential combination of back-projected images at each voxel plane of the volume the 3-D droplet and ligament positions can be readily obtained. Further improvement of intensity reconstruction may be achieved by a iterative tomographic reconstruction, namely multiplicative algebraic reconstruction technique (SMART). These improvements are documented by comparing slices of the averaged 3-D Shadowgraph intensity of the hollow cone spray orthogonal to the flow. The investigations were further substantiated with simulations using synthetic data to estimate reconstruction quality at increasing droplet densities.
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on the implementation of tomographic Shadowgraphy for spray diagnostics
2011Co-Authors: Joachim Klinner, Christian WillertAbstract:This contribution introduces 3-D Shadowgraphy which is capable of resolving the placement of the liquid phase within a certain spray volume both spatially and temporally. The method is based on a multiple view camera setup and inline illumination provided by current pulsed LEDs. The observed volume is calibrated with a traversed micro target. A comparison is made between several photogrammetric and polynomial least square camera calibration techniques regarding their accuracy in deep volume calibration at magnifications close to 1 : 1. A new calibration method is suggested which derives volume calibration from multiple planar homographies at equally spaced z-planes. After an sequential combination of back-projected images at each voxel plane the 3-D droplet positions can be readily obtained. The quality of spray reconstruction was investigated using experimental data from multiple view Shadowgraphs of hollow cone and flat fan water sprays. The investigations were further substantiated with simulations using synthetic data.
Farzan Parsinejad - One of the best experts on this subject based on the ideXlab platform.
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A mathematical model for Schlieren and Shadowgraph images of transient expanding spherical thin flames
Journal of Engineering for Gas Turbines and Power, 2004Co-Authors: Farzan Parsinejad, Matyas Matlo, Mohamad MetghalchiAbstract:Optical behavior of spherical flames is investigated using both Schlieren and Shadowgraph methods. A mathematical model has been developed to predict the intensity of refracted light beams interacting with a transient expanding thin flame. Experimental facilities have been built to visualize transient expanding spherical flames. The facilities include a cylindrical chamber with two end glasses for optical observation. Shadowgraph and Schlieren pictures of flame propagation have been taken using a high-speed charged coupled device camera. Experimental results are in very good agreement with those predicted by the theoretical model. Schlieren and Shadowgraph techniques have also been used to view smooth, cracked and cellular flames; these techniques will be useful in future in studies to determine the stability of propagating flame.
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Schlieren and Shadowgraph Images of Transient Expanding Spherical Thin Flames
Energy Conversion, 2002Co-Authors: Matyas Matlo, Farzan Parsinejad, Hameed MetghalchiAbstract:Experimental facilities have been built to visualize transient expanding spherical flames. Facilities include a cylindrical chamber with two end glasses for optical observation. Shadowgraph and Schlieren pictures of flame propagation have been taken using a high speed Charged Coupled Device (CCD) camera. In this paper the optical behavior of spherical flames has been investigated using both Schlieren and Shadowgraph methods. A mathematical model has been developed to predict the intensity of refracted light beams interacting with a transient expanding thin flame. Experimental results are in very good agreement with theoretical model. Schlieren and Shadowgraph techniques have also been used to view smooth, cracked and cellular flames, which are useful in determining the stability of propagating flame.Copyright © 2002 by ASME
Y. H. Elbashar - One of the best experts on this subject based on the ideXlab platform.
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Design and test of high-efficiency dual-element laser diffuser for large-field automotive Shadowgraphy
Journal of Optics, 2020Co-Authors: H S Ayoub, Wessam M Hussein, Ashraf F. El-sherif, Y. H. ElbasharAbstract:A new design is developed for compact-size and lightweight laser beam diffuser of two rad divergence (± 1 rad ≈ ± 60°). The design combines diffractive–refractive beam shaping optics, and it consists of a 532 nm military laser pointer, equipped with a laser dot matrix beam shaper and a rod lens. The non-Gaussian laser beam is spread into a relatively homogenous large-field illumination. This design is a low-cost optical configuration, which enabled large-field automotive laser Shadowgraphy and was found to be very useful in similar practice situations, where a laser beam of high divergence is required. The diffuser setup was tested successfully in composing laser Shadowgraph of 2 m height and 18 m width for a test car interior, where both direct and indirect driver’s fields of views are presented.
