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This thesis outlines two advancements in the field of limited data absorption tomography. First, a novel reconstruction algorithm integrating the use of level set methods is presented that incorporates the additional a priori knowledge of a distinct interface between the species of interest and co-flow. The added a priori further reduces the ill-posedness of the system to produce a final concentration distribution that explains the laser absorption measurements and is qualitatively consistent with advection/diffusion transport. The algorithm is demonstrated by solving a simulated laser tomography experiment on a turbulent methane plume, and is compared with the current state-of-the-art reconstruction algorithm. Given the limited number of attenuated measurements, accurate reconstructions are also highly dependent on the locations sampled by the measurement array. This thesis displays how the mathematical properties of the coefficient matrix, A, formed by the locations of the lasers, are related to the information content of the attenuation data using a Tikhonov reconstruction framework. This formulation, in turn, becomes a basis for a beam arrangement design algorithm that minimizes the reliance on additional assumed information about the concentration distribution. Using genetic algorithms, beam arrangements can be optimized for a given application by incorporating physical constraints of the beam locations. The algorithm is demonstrated by optimizing unconstrained and constrained arrangements of light sources and detectors. Simulated experiments are performed to validate the optimality of the arrangements.

This thesis outlines two advancements in the field of limited data absorption tomography. First, a novel reconstruction algorithm integrating the use of level set methods is presented that incorporates the additional a priori knowledge of a distinct interface between the species of interest and co-flow. The added a priori further reduces the ill-posedness of the system to produce a final concentration distribution that explains the laser absorption measurements and is qualitatively consistent with advection/diffusion transport. The algorithm is demonstrated by solving a simulated laser tomography experiment on a turbulent methane plume, and is compared with the current state-of-the-art reconstruction algorithm. Given the limited number of attenuated measurements, accurate reconstructions are also highly dependent on the locations sampled by the measurement array. This thesis displays how the mathematical properties of the coefficient matrix, A, formed by the locations of the lasers, are related to the information content of the attenuation data using a Tikhonov reconstruction framework. This formulation, in turn, becomes a basis for a beam arrangement design algorithm that minimizes the reliance on additional assumed information about the concentration distribution. Using genetic algorithms, beam arrangements can be optimized for a given application by incorporating physical constraints of the beam locations. The algorithm is demonstrated by optimizing unconstrained and constrained arrangements of light sources and detectors. Simulated experiments are performed to validate the optimality of the arrangements.

This research is for the implementation of non-intrusive measurement techniques in the study of high temperature pipe flow. A low pressure, laboratory scale hybrid rocket motor simulator was built to achieve high temperatures with various gases. A quartz test section was designed, built, and implemented into the existing test setup to accommodate the laser beam of the existing Tunable Diode Laser Absorption Spectrometer (TDLAS) system which was designed to observe water vapor. A super-heated water vapor injector was designed to obtain the desired water vapor concentrations. Flow characteristics were simultaneously recorded using the existing TDLAS system and the DAQ system for temperatures for later comparison. A numerical study using a commercial CFD package was used to predict the flow characteristics at certain locations for experimental comparison. Based on this study, it is concluded that the TDLAS can be used to make real time temperature measurements of heated internal gas flows.

<div>Laser-absorption spectroscopy (LAS) is widely used for providing non-intrusive and quantitative measurements of gas properties (such as temperature and absorbing species mole fraction) in combustion environments. However, challenges may arise from the line-of-sight nature of LAS diagnostics, which can limit their spatial resolution. Further, time-resolution of such techniques as scanned direct-absorption or wavelength-modulation spectroscopy is limited by the scanning speed of the laser and the optical bandwidth is often limited by a combination of a laser's intrinsic tunability and its scanning speed. The work presented in this dissertation investigated how recent advancements in mid-IR camera technology and lasers can be leveraged to expand the spatial, temporal, and spectral measurement capabilities of LAS diagnostics. Novel laser-absorption imaging and ultrafast laser-absorption spectroscopy diagnostics are presented in this dissertation. In addition, the high-pressure combustion chamber (HPCC) and high-pressure shock tube (HPST) were designed and built to enable the study of, among others, energetic material combustion, spectroscopy, non-equilibrium and chemistry using optical diagnostics.<br></div><div><br></div>

This research focuses on developing optical sensing systems for 2D and 3D spatial monitoring of temperature and concentration distribution profiles of complex or reacting gas flows. Non-invasive, species specific and sensitive nature of monitoring allows spatial information to be extracted from harsh environments with poor physical access, allowing validation of computational models or process monitoring. This is suitable for processes like combustion engines or sealed atmospheric cloud chambers. A novel line-of-sight (LOS) Tunable Diode Laser Absorption Spectroscopy(TDLAS) system using a preselected laser diode centred at 7212.88 cm-1 was first designed to monitor the change of relative humidity (water vapour concentration) during an expansion process within the Manchester Ice Cloud Chamber (MICC), operating from atmospheric pressure, down to 0.7 atm. The experimental results were validated with an Aerosol Cloud Precipitation Interaction Model (ACPIM) simulation, feasible for tomography applications. The MICC shares similar combustion monitoring challenges such as minimal optical access or reactive gas flows. The TDLAS system developed for the MICC was then used as a foundation design for a TDLAS tomography setup capable of conducting temporal two-dimensional (2D) and three-dimensional (3D) concentration and temperature imaging. This system uses the principle of two-line thermometry, centred within the near infrared (NIR) region of 7181.93cm-1 and 7179.8 cm-1. The laser was divided into 4 simultaneous parallel beams using a 1 × 4 fiber coupler (4 LOS). Using a motorised platform, the beams were projected at 0.5° interval, from 0° to 179° angle within 3.6 s, around the exhaust of two asymmetrical shaped flame burners. A total of 360 projection slices comprised of 1440 integrated absorbance data were used per tomogram reconstruction. By solving for the spatial distribution of temperature first, the concentration distribution of water vapour could be then calculated. Reconstruction algorithms (Filtered Back Projection, Fourier Slice Reconstruction and Direct Fourier Reconstruction (DFR)) were compared using a range of criteria. The DFR method was selected as the best method at 700 zero padding, with a spatial in-plane resolution of 1-2 lp/cm, pixel resolution of 128 by 128, thermocouple temperature validations of ±5°C and a relative mean error performance of 8.12%. The concentration could not be validated due to the lack of a mass spectrometer.3D volumetric monitoring results took 36 seconds to complete, and was constructed using 10 interpolated parallel, 1 cm height interval spaced tomograms. Independent vertical slices along the x-axis and y-axis could also be extracted. The temporal results were also successfully conducted and consisted of a quick succession of 16 experiments at a temporal resolution of 0.28 frames per second. A tomographic system that performs 3D and 2D temporal sensing was successfully developed and validated. Although 3D work was conducted using planar imaging or hyperspectral tomography, no work has been conducted so far using NIR TDLAS systems to date.

Long path optical waveguides can be used in optical absorption measurements to increase the optical path length and, thus, the overall absorption of a sample. Recently, 1m long coiled Liquid Waveguide Capillary Cells (LWCC) have been used by analytical spectroscopists to measure the absorption strength of weakly absorbing liquids. However, most of these measurements have used conventional light sources such as Xenon or Halogen lamps and not spectroscopic laser sources. In this thesis study, we used a LWCC absorption waveguide and a laser light source to measure, for the first time to our knowledge, the optical transmission through several water or liquid samples. It was found upon using the LWCC waveguide, the coherent laser light source tended to produce larger variability (>±15%) in the measurements of transmission readings than that for a conventional absorption cell or a conventional light source. This was especially evident when the LWCC waveguide was chemically cleaned with an acid and a base solution between each sample run as directed by the manufacturer. The non-coherent optical sources, Halogen lamp and Xenon arc lamp, produced more stable (±3%) transmission measurements. Finally, using a Helium Neon laser scattered off a diffuse reflecting surface was found to produce moderate variability (±7%), but this was much less than the coherent Helium Neon laser alone. It was concluded that the use of the coherent source was more susceptible than the non-coherent source to small changes in the reflectivity or index of refraction along the wall of the coiled LWCC waveguide. Our results are consistent with recent work by Barwicz and Haus, and by Lytle and Splawn who saw a large dependence of the transmission through a hollow straight waveguide upon changes in the polarization and input angle of the laser beam directed into the waveguide.

Tunable diode laser absorption spectroscopy using an external cavity diode laser operating in the infra-red has been developed to monitor CO2 in the freestream of the Longshot hypervelocity facility at the Von Karman Institute for Fluid Dynamics. The Longshot facility offers a unique European facility for ground testing and numerical validation applications, however, some of the traditional data rebuilding aspects are in question. A non-intrusive absorption sensor could significantly aid in improving the knowledge of freestream static values thereby improving the models used in data rebuilding and numerical simulation. The design of such a sensor also expands the spectroscopic capabilities of the Von Karman Institute. The absorption sensor is designed around the single P12 (00001)-(30013) rovibrational transition near 1.6µm (6218.09cm-1 specifically) which yields relatively weak direct absorption levels at about 3.5% per meter for typical Longshot freestream conditions. However, when handled carefully, adequate signal-to-noise can be acquired to exploit significant flow information. By being able to operate in this range, total sensor cost can be easily an a factor of two or more cheaper than sensors designed for the deeper infrared. All sensor elements were mounted to a compact portable optics bench utilizing single-mode optical fibers to allow for quick installation at different facilities by eliminating tedious optical realigning. Scans at 600Hz were performed over 20ms of the 40ms test time to extract core static temperature, pressure and velocity. These results are compared with the current state of the Longshot data rebuild method. The non-uniform flow properties of the shear layer and test cabin rested gas accumulation was of an initial concern. The temperature and density gradients along with significant radial velocity components could result in DLAS temperature, pressure and velocity that are significantly different than that of the target freestream inviscid core values. Fortunately, with the proper selection of the P12 rotational number, this effect could be more or less ignored as the higher temperature and lower density gas of this region is relatively transparent. Ultimately, acquired temperature and density were moderately accurate when compared to Longshot rebuilt results owing primarily to the baseline extraction which poses issues for such low absorption signals. However, the extracted velocity data are quite accurate. This is a definite puls for the sensor as the freestream enthalpy of cold hypersonic facilities is dictated primarily by the kinetic energy contribution. Being able to compare velocity gives insight to the level of vibration non-equilibrium in the flow. The velocity of the DLAS and the Longshot rebuild are quite close. This adds more weight to the argument that vibrational excitation is very low (if present at all) in the free stream and that the van de derWaals equation of state usage and constant specific heat assumption might be an adequate model for the data rebuild after all.

Lean, premixed combustion has enjoyed increased application due to the need to reduce pollutant emissions. Unfortunately, operating the flame at lean conditions increases susceptibility to thermoacoustic (TA) instability. Self-excited TA instabilities are a result of the coupling of the unsteady heat release rate of the flame with the acoustics of the combustion chamber. The result is large pressure oscillations that degrade performance and durability of combustion systems. Industry currently has no reliable tool to predict instabilities a priori. CFD simulations of full-scale, turbulent, reacting flows remain unrealizable. The work in this paper is part of a study that focuses on developing compact models of TA instabilities, i.e. acoustics and flame dynamics. Flame dynamics are defined as the response in heat release to acoustic perturbations. Models of flame dynamics can be coupled with models of combustor enclosure acoustics to predict TA instabilities. In addition, algorithms to actively control instabilities can be based on these compact models of flame dynamics and acoustics. The work outlined in this thesis aims at determining the flame dynamics model experimentally. Velocity perturbations are imparted on laminar and turbulent flames via a loudspeaker upstream of the flame. The response of the flame is observed through two measurements. Hydroxyl radical (OH*) chemiluminescence indicates the response in chemical reaction rate. Tunable Diode Laser Absorption Spectroscopy (TDLAS), centered over two water absorption features, allows a dynamic measurement of the product gas temperature. The response in product gas temperature directly relates to the enthalpy fluctuations that couple to the acoustics. Experimental frequency response functions of a laminar, flat-flame burner and a turbulent, swirl-stabilized combustor will be presented as well as empirical low-order models of flame dynamics. / Master of Science

Cette thèse présente le développement d’une méthode ALE pour la modélisation del’interaction laser–plasma. La particularité de cette méthode est l’utilisation d’une étape de projectiond’ordre élevé. Cette étape de projection consiste en une interpolation conservative des quantitésconservatives du maillage Lagrangien sur un maillage régularisé. Afin d’éviter les oscillationsnumériques non-physiques, les flux numériques d’ordre élevé sont combinés avec des fluxnumériques d’ordre moins élevé. Ces flux numériques sont obtenu en considérant les quantitésconservatives constantes par morceaux. Cette méthode pour la discrétisation cellule–centrée consisteà préserver les maximums locaux pour la densité, la vitesse et l’énergie interne. Aspects particuliersde la méthode sont appliquées pour la projection la quantité de mouvement pour la discrétisation’staggered’. Nous l’utilisons ici dans le cadre de la projection sous la forme de la méthode FluxCorrection Remapping (FCR). Dans cette thèse le volet applicatif concerne la modélisation del’interaction d’un laser énergétique avec de plasma et des matériaux microstructures. Un intérêtparticulier est porté à la modélisation de l’absorption du laser par une mousse de faible densité.L’absorption se fait à deux échelles spatiales simultanément. Ce modèle d’absorption laser à deuxéchelles est mis en oeuvre dans le code PALE hydrodynamique. Les simulations numériques de lavitesse de pénétration du laser dans une mousse à faible densité sont en bon accord avec lesdonnées expérimentales. / This thesis presents the overview and the original contributions to a high–orderArbitrary Lagrangian–Eulerian (ALE) method applicable for the laser–generated plasma modeling withthe focus to a remapping step of the ALE method. The remap is the conservative interpolation of theconservative quantities from a low–quality Lagrangian grid onto a better, smoothed one. To avoidnon–physical numerical oscillations, the high–order numerical fluxes of the reconstruction arecombined with the low–order (first–order) numerical fluxes produced by a standard donor remappingmethod. The proposed method for a cell–centered discretization preserves bounds for the density,velocity and specific internal energy by its construction. Particular symmetry–preserving aspects of themethod are applied for a staggered momentum remap. The application part of the thesis is devoted tothe laser radiation absorption modeling in plasmas and microstructures materials with the particularinterest in the laser absorption in low–density foams. The absorption is modeled on two spatial scalessimultaneously. This two–scale laser absorption model is implemented in the hydrodynamic codePALE. The numerical simulations of the velocity of laser penetration in a low–density foam are in agood agreement with the experimental data.