The purpose of this study is to numerically investigate the turbulence modulation of polydisperse particles in a square particle-laden jet. Turbulence modulation describes the effects of fluctuating velocity and intensity when the particles and continuous fluid interact in a turbulent flow field. The rate at which turbulence modulation is altered is dependent upon parameters such as particle size, mass loading, Stokes number, coupling, volume fraction and mechanisms of turbulence modulation. This study modifies the analytical model developed by Yarin and Hetsroni (1993) to account for the transitional drag regime for coarse polydisperse particles. The particles under study are dilute, inert and spherical, with relatively high Stokes numbers, and classified as having two-way coupling with the fluid. The new analytical model is compared to numerical results using the Computational Fluid Dynamics (CFD) software FLUENT (ANSYS, Inc.). The turbulence model employed is the standard k-ε model. This study will analyze the effects of varying mass content and particle ratios to investigate how turbulence modulation is influenced. The new model and the CFD results show good agreement in the cases where the mass contents of each particle size are equal. This study will also look into the effects of polydispersion, and the concentration distribution, for indoor air applications. It was found that, in certain cases, the monodisperse assumption slightly over-predicts the concentration distribution in the enclosed region. / Master of Science

No / River morphological processes are among the most complex and least understood phenomenon in nature. Recent research indicates that the braiding of marine waterways of the estuary zone occurs at an aspect ratio similar to the alluvial braided river. The instability of complex sporadic fluvial processes at river-sea interface is responsible for bar formation in alluvial as well as in marine waterbodies Due to the lack of knowledge of flow characteristics around bar, the flow structure around the sand bar is analyzed. The bursting events play the crucial role in understanding the fluvial characteristics in the vicinity of submerged structure. The study of bursting events around the mid-channel bar is only done by the present author. The effect of submergence ratio on the turbulence behavior in the proximity of bar is analyzed in this study. The flow turbulence generated by the mid-channel bar is also analyzed in detail. The extreme turbulent burst is segregated from low intensity turbulent events by using the hole size concept. The effect of hole size on the parameter Dominance Function is analysed which is not yet studied by any researcher for mid-channel bar. The Momentum Dominance Function (MDF) parameter increases with increase in the Hole Size. This indicates that the magnitude of upward flux increases with increase in the hole size. The effect of bar height on the turbulent burst which is not yet studied by any researchers is analyzed in the present research. The joint probability distribution of bursting events is modeled using the Gram-Charlier bivariate joint probability function. The joint probability distribution gives the details of probabilistic structure of flow in the vicinity of bar. The effect of bar is predominant only in the lower flow layer. The joint probability distribution graph becomes more eccentric toward the dominant quadrants with increase in the submergence ratio. This indicates that the probability of dominant events further increases with increase in the submergence ratio.

No / The local parameters for kerosene–water upward flow are measured in a vertical pipe of 77.8 mm inner diameter at 4200 mm from the inlet(L/D = 54) using hot-film and dual optical probes. The effect of superficial water velocity and volumetric quality on radial distribution of two-phaseflow parameters is investigated. The results show the following: (i) the profiles of volume fraction and drop frequency are very similar, and increasing superficial water velocity at low volumetric qualities (<18.6%) change the profile from a convex shape with peak at the pipe centreline to uniform then to concave shape with peak near the wall; (ii) the profiles of drop cut chord change from a parabolic shape with peak at centreline for lows uperficial water velocities to a flat shape at higher superficial water velocity, and the area-averaged drop diameter decreases with higher superficial water velocities for all volumetric qualities; (iii) velocity profiles for both phases have shapes similar to single phase flow, flatter at higher values of superficial water velocity and volumetric quality and centreline peaked at low superficial water velocities and volumetric qualities; (iv) the slip velocity decreases with radial distance having a peak at centreline and zero values near the wall; (v) introducing kerosene drops into single phasewater flow results in a sharp increase in turbulent intensity, particularly at low water velocity, and the difference between the single phase and two-phase flow turbulence intensities decreases with higher superficial water velocities and (vi) the results show that interfacial area concentration increased with higher volumetric quality and higher number of bubbles thereby increases the contact area between the two phases.

Influence of dust particles on the characteristics of premixed methane-air flames has been studied in this dissertation. Experiments are performed in a Bunsen burner type experimental set-up called Hybrid Flame Analyzer (HFA), which can be used to measure the burning velocity of gas, dust, and hybrid (gas and dust) premixed flames at constant pressure operating conditions. In the current study, analysis of particle-gas-air system of different types of dust particles (at particle size, dp = 75-90 µm) in premixed methane-air (ϕg = 0.8, 1.0 and 1.2) flames. Coal, sand, and sodium bicarbonate particles are fed along with a premixed methane-air mixture at different concentrations (λp = 0-75 g/m3) in both laminar and turbulent conditions. First, the variation of laminar burning velocity with respect to the concentration of dust particles, and type of dusts are investigated for different equivalence ratios. Second, the laminar premixed flame extinction with inert and chemical suppressant particles are studied. Third, the variation of turbulent burning velocity of these hybrid mixtures are investigated against different turbulent intensities apart from the different concentrations and types of dusts. Fourth, the radiative fraction of heat released from turbulent gas-dust premixed flames are also presented against the operating parameters considered. Combustible dust deflagration hazard is normally quantified using the deflagration index (Kst) measured using a constant volume explosion sphere, which typically is a sealed 20-liter metal sphere where a premixed mixture is ignited at the center and the progression of the resulting deflagration wave is recorded using the pressure measured at the vessel wall. It has been verified from prior studies that the quantification of the turbulence by this method is questionable and there is a need to analyze the controlling parameters of particle-gas-air premixed system accurately through a near constant pressure operated experimental platform. Thus, the main objective of this study is to analyze the influence of dust particles on premixed methane-air flames at near constant pressure conditions. The turbulent burning velocity is calculated by averaging the measured flame heights and the laminar burning velocity is calculated through the premixed cone angle measurements from several high-speed shadowgraph images obtained from the experiments. The turbulent intensity and length scale of turbulence generated by a perforated plate in the burner is quantified from the hot-wire anemometer measurements. Radiative heat flux is also measured for each of the turbulent test conditions. The outcomes from these experiments are: 1. An understanding of the variation of turbulent burning velocity of gas-dust premixed flames as a function of dust type, turbulent intensity, integral length scale, dust concentration and gas phase mixture ratio. 2. An understanding of the flame extinction characteristics and variation of laminar burning velocity of gas-dust premixed flames as a function of dust concentration and gas phase mixture ratio. 3. Quantify the radiative heat flux and radiative fraction of heat released from gas-dust turbulent premixed flames as a function of dust type, turbulent intensity, dust concentration and gas phase mixture ratio. Dust type and concentration play an important role in deciding the trend in the variation of both laminar (SL) and turbulent burning velocity (ST). Coal particles, with the release of volatile (methane), tend to increase burning velocities except for fuel rich conditions and at higher coal concentrations at larger turbulent intensities. At a higher turbulent intensity and larger concentrations, higher ST values are observed with the addition of sand. Sodium bicarbonate addition, with the release of CO2 and H2O, decreased the burning velocity at all the concentrations, turbulent intensities and equivalence ratios. Laminar flame extinction was observed with the addition of sand and sodium bicarbonate particles at conditions exceeding certain critical dust concentrations. These critical concentrations varied with the equivalence ratios of gaseous premixed flames. The turbulence modulation exhibited by particles and particle concentration is evident in these observations. The independent characteristic time scale analysis performed using the experimental data provided further insights to the results. The chemical and convective times in gas phase confirm the broadened preheat thin reaction zone regime in the current test cases, which has an effect of attenuating turbulence and thereby the resulting turbulent burning velocity. The particle time scale analysis (Stokes number) show that the effect of particles and particle concentration is to slightly enhance the turbulence and increase the turbulent burning velocity at lower concentrations. However, the time scale analysis of particle vaporization (vaporization Damköhler number) indicate an increase in the vaporization rate for particles (coal and sodium bicarbonate) resulting in a decrease in their turbulent burning velocities at higher concentrations and turbulent intensities. Sodium bicarbonate has higher evaporation rate than coal at same level of turbulence and the absence of this effect for inert (sand) results in higher turbulent burning velocities at higher concentrations. An increase in the turbulent intensity increases the vaporization rate of particles. The investigation on radiative fraction of heat released by methane-air-dust turbulent premixed flames identified that, the addition of dust particles increases the radiative fraction irrespective of the dust type due to the radial and axial extension of flame. A unified approach to couple this multiple complex phenomenon of turbulence, particle interaction, particle vaporization and combustion in particle laden premixed gaseous flames is the direction for future research.

Yes / When using point measurement for environmental or sediment laden flows, there is well-recognised risk for not having aligned measurements that causes misinterpretation of the measured velocity data. In reality, these kinds of mismeasurement mainly happen due to the misinterpretation of bed orientation caused by the complexity of its determination in natural flows, especially in bedload laden or rough bed flows. This study proposes a novel bed realignment method to improve the measured data benchmarking by three-dimensional (3D) bed profile orientation and implemented it into different sets of experimental data. More specifically, the effects of realignment on velocity profile and streamwise turbulence structure measurements were investigated. The proposed technique was tested against experimental data collected over a water-worked and an experimentally arranged well-packed beds. Different from the well-packed rough bed, the water-worked bed has been generated after long sediment transport and settling and hence can be used to verify the proposed bed-alignment technique thoroughly. During the flow analysis, the corrected velocity, turbulence intensity and Reynolds stress profiles were compared to the theoretical logarithmic law, exponential law and linear gravity (universal Reynolds stress distribution) profiles, respectively. It has been observed that the proposed method has improved the agreement of the measured velocity and turbulence structure data with their actual theoretical profiles, particularly in the near-bed region (where the ratio of the flow measurement vertical distance to the total water depth, z/h, is limited to ≤0.4).

Face aux normes actuelles et futures de plus en plus draconiennes en termes d’émissions polluantes, les constructeurs automobiles cherchent en permanence à améliorer le rendement des moteurs à allumage commandé. L’une des voies efficaces et applicables à court terme pour réduire les émissions de dioxyde de carbone (CO2) consiste à réduire la cylindrée des moteurs tout en conservant leur performance grâce à la sur-alimentation : c’est l’approche de l’éco-suralimentation ou « downsizing ». L’une des particularités de ce mode de fonctionnement est le fort niveau de pression et de taux de dilution dans lequel se propage la flamme de prémélange. La simulation de la combustion turbulente de prémélange est devenue un outil incontournable pour la R&D. Toutefois, les hypothèses sur lesquelles reposent les modèles de combustion, tout particulièrement le modèle de flammelettes, peuvent être sujettes à discussion dans le cas d’un fonctionnement de type « downsizing ». Le but de ce travail de thèse est donc d’étudier expérimentalement les régimes de combustion de manière à valider ou non l’utilisation de ces modèles. Les grandeurs caractéristiques de la turbulence ont alors été caractérisées lors de la phase de compres-sion pour différentes pressions d’admission à l’aide de la vélocimétrie par imagerie de particules. La vitesse de combustion de laminaire a, quant à elle, été estimée à partir d’un mécanisme cinétique réduit. L’utilisation de la tomographie laser par diffusion de Mie avec et sans suivi temporel, nous a permis de caractériser la vitesse de combustion turbulente et la structure du front de flamme pour différentes pressions d’admission et différents taux de dilution. Lors de cette étude, nous avons ainsi pu mettre en évidence une cassure dans l’évolution de la PMI et de la vitesse de combustion turbulente à partir d’un taux de dilution de 25% : cette cassure a été reliée à la transition entre le régime de flammelette et le régime des flammes plissées épaissies. / Faced with the current and future more and more drastic standards for pollutant emissions, car manufacturers try to improve the efficiency of Spark Ignition engine. One effective and applicable ways to reduce the greenhouse emissions (CO2) in the short run is based on the reduction of the engine size while preserving their performance thank to turbocharging: eco-supercharging or « downsizing » approaches. One of the characteristics of this operating mode is the high level of the pressure and of the dilution rate of the medium in which the premixed flame propagates. The simulation of turbulent premixed flame is nowadays an indispensable tool for R&D. However, the assumptions on which the combustion models are based, particularly the flamelet model, can be prone to discussion in the « downsizing » conditions. The objective of this work is thus to study experimentally the combustion regimes in order to validate or not the use of these models. Turbulence parameters and flow fields were then characterized out during the compression stroke for several intake pressures by using Particle Imaging Velocimetry technique. The laminar burning velocity was estimated by using reduced chemical kinetic schemes. The Mie scattering laser tomography technique with and without temporal follow-up, enabled us to characterize the turbulent burning velocity and the flame front structure for different intake pressures and dilution rates. In this study, a break in the evolution of the IMEP and the turbulent burning velocity for a dilution rate of 25% has been obtained: this break was linked to the transition between the flamelet zone and the distributed reaction zones.