Browsing by Author "Li, Xuesong"

Now showing 1 - 8 of 8
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    50-kHz-rate 2D imaging of temperature and H2O concentration at the exhaust plane of a J85 engine using hyperspectral tomography
    Ma, Lin; Li, Xuesong; Sanders, Scott T.; Caswell, Andrew W.; Roy, Sukesh; Plemmons, David H.; Gord, James R. (Optical Society of America, 2013-01-01)
    This paper describes a novel laser diagnostic and its demonstration in a practical aero-propulsion engine (General Electric J85). The diagnostic technique, named hyperspectral tomography (HT), enables simultaneous 2-dimensional (2D) imaging of temperature and water-vapor concentration at 225 spatial grid points with a temporal response up to 50 kHz. To our knowledge, this is the first time that such sensing capabilities have been reported. This paper introduces the principles of the HT techniques, reports its operation and application in a J85 engine, and discusses its perspective for the study of high-speed reactive flows. (C) 2013 Optical Society of America
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    A closed-form method for calculating the angular distribution of multiply scattered photons through isotropic turbid slabs
    Sun, Xueqiang; Li, Xuesong; Ma, Lin (Optical Society of America, 2011-11-01)
    This paper develops a method for calculating the angular distribution (AD) of multiply scattered photons through isotropic turbid slabs. Extension to anisotropic scattering is also discussed. Previous studies have recognized that the AD of multiply scattered photons is critical for many applications, such as the design of imaging optics and estimation of image quality. This paper therefore develops a closed-from method that can accurately calculate the AD over a wide range of conditions. Other virtues of the method include its simplicity in implementation and its prospective for extension to anisotropic scattering. (C) 2011 Optical Society of America
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    Method to correct the distortion caused by amplified stimulated emission as motivated by LIF-based flow diagnostics
    Li, Xuesong; Zhao, Yan; Ma, Lin (Optical Society of America, 2012-04-01)
    Amplified stimulated emission (ASE) represents a significant issue in two-photon laser-induced fluorescence (TPLIF). The ASE effects are nonlinear and nonlocal, i.e., the ASE effects distort the LIF signal nonlinearly, and the distortion at one location depends on conditions at other locations. In this sense, the ASE effects pose a greater challenge to quantitative TPLIF than quenching and ionization. This work therefore seeks a method to correct such distortion. The method uses two LIF measurements, one with low signal-to-noise ratio (SNR) and negligible ASE distortion and another with high SNR but significant distortion, to generate a faithful measurement with high SNR. Extensive simulations were performed to evaluate the performance of this method for practical applications. c 2012 Optical Society of America OCIS codes: 300.2530, 300.6420, 120.1740.
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    Multi-dimensional Flow and Combustion Diagnostics
    Li, Xuesong (Virginia Tech, 2014-06-10)
    Turbulent flows and turbulent flames are inherently multi-dimensional in space and transient in time. Therefore, multidimensional diagnostics that are capable of resolving such spatial and temporal dynamics have long been desired; and the purpose of this dissertation is to investigate three such diagnostics both for the fundamental study of flow and combustion processes and also for the applied research of practical devices. These multidimensional optical diagnostics are a 2D (two dimensional) two-photon laser-induced fluorescence (TPLIF) technique, a 3D hyperspectral tomography (HT) technique, and a 4D tomographic chemiluminescence (TC) technique. The first TPLIF technique is targeted at measuring temporally-resolved 2D distribution of fluorescent radicals, the second HT technique is targeted at measuring temperature and chemical species concentration at high speed, and the third TC technique is targeted at measuring turbulent flame properties. This dissertation describes the numerical and experimental evaluation of these techniques to demonstrate their capabilities and understand their limitations. The specific aspects investigated include spatial resolution, temporal resolution, and tomographic inversion algorithms. It is expected that the results obtained in this dissertation to lay the groundwork for their further development and expanded application in the study of turbulent flow and combustion processes.
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    Numerical and experimental validation of a three-dimensional combustion diagnostic based on tomographic chemiluminescence
    Cai, Weiwei; Li, Xuesong; Li, Fei; Ma, Lin (Optical Society of America, 2013-03-25)
    Three-dimensional (3D) measurements are highly desirable both for fundamental combustion research and practical monitoring and control of combustion systems. This work discusses a 3D diagnostic based on tomographic chemiluminescence (TC) to address this measurement need. The major contributions of this work are threefold. First, a hybrid algorithm is developed to solve the 3D TC problem. The algorithm was demonstrated in extensive tests, both numerical and experimental, to yield 3D reconstruction with high fidelity. Second, an experimental approach was designed to enable quantifiable metrics for examining key aspects of the 3D TC technique, including its spatial resolution and reconstruction accuracy. Third, based on the reconstruction algorithm and experimental results, we investigated the effects of the view orientations. The results suggested that for an unknown flame, it is better to use projections measured from random orientations than restricted orientations (e.g., coplanar orientations). These findings are expected to provide insights to the fundamental capabilities of the TC technique, and also to facilitate its practical application.
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    Practical aspects of implementing three-dimensional tomography inversion for volumetric flame imaging
    Cai, Weiwei; Li, Xuesong; Ma, Lin (Optical Society of America, 2013-11-01)
    Instantaneous three-dimensional (3D) measurements have been long desired to resolve the spatial structures of turbulent flows and flame. Previous efforts have demonstrated tomography as a promising technique to enable such measurements. To facilitate the practical application, this work investigated four practical aspects for implementing 3D tomographic under the context of volumetric combustion diagnostics. Both numerical simulations and controlled experiments were performed to study: (1) the termination criteria of the inversion algorithm; (2) the effects of regularization and the determination of the optimal regularization factor; (3) the effects of a number of views; and (4) the impact of the resolution of the projection measurements. The results obtained have illustrated the effects of these practical aspects on the accuracy and spatial resolution of volumetric tomography. Furthermore, all these aspects are related to the complexity and implementing cost (both hardware cost and computational cost). Therefore, the results obtained in this work are expected to be valuable for the design and implementation of practical 3D diagnostics. (C) 2013 Optical Society of America
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    Scaling Law for Photon Transmission through Optically Turbid Slabs Based on Random Walk Theory
    Li, Xuesong; Ma, Lin (MDPI, 2012-03-01)
    Past work has demonstrated the value of a random walk theory (RWT) to solve multiple-scattering problems arising in numerous contexts. This paper's goal is to investigate the application range of the RWT using Monte Carlo simulations and extending it to anisotropic media using scaling laws. Meanwhile, this paper also reiterates rules for converting RWT formulas to real physical dimensions, and corrects some errors which appear in an earlier publication. The RWT theory, validated by the Monte Carlo simulations and combined with the scaling law, is expected to be useful to study multiple scattering and to greatly reduce the computation cost.
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    Volumetric imaging of turbulent reactive flows at kHz based on computed tomography
    Li, Xuesong; Ma, Lin (OSA Publishing, 2014-02-21)
    Diagnostics with three-dimensional (3D) spatial resolution and rapid temporal resolution have been long desired to resolve the complicated turbulence-chemistry interactions. This paper describes a method based on based on tomographic chemiluminescence (TC) to address this diagnostic need. The TC technique used multiple cameras to simultaneously record CH* chemiluminescence emitted by turbulent flames from different view angles. A 3D tomographic algorithm was then applied to reconstruct the instantaneous flame structures volumetrically. Both experimental and computational studies have been conducted to demonstrate and validate the 3D measurements. Experimental results were obtained instantaneously at kHz temporal rate, in a volume of 16 × 16 × 16 cm3, and with a spatial resolution estimated to be 2~3 mm. Computations were conducted to simulate the experimental conditions for comparison and validation.