Dissertations / Theses on the topic 'Gas-particle flows'
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Strömgren, Tobias. "Model predictions of turbulent gas-particle shear flows." Doctoral thesis, KTH, Mekanik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12135.
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A turbulent two-phase flow model using kinetic theory of granularflows for the particle phase is developed and implmented in afinite element code. The model can be used for engineeringapplications. However, in this thesis it is used to investigateturbulent gas-particle flows through numerical simulations. The feedback from the particles on the turbulence and the meanflow of the gas in a vertical channel flow is studied. In particular,the influence of the particle response time, particle volumefraction and particle diameter on the preferential concentration ofthe particles near the walls, caused by the turbophoretic effect isexplored. The study shows that when particle feedback is includedthe accumulation of particles near the walls decreases. It is also foundthat even at low volume fractions particles can have a significant impacton the turbulence and the mean flow of the gas. The effect of particles on a developing turbulent vertical upward pipeflow is also studied. The development length is found to substantiallyincrease compared to an unladen flow. To understand what governs thedevelopment length a simple estimation was derived, showing that itincreases with decreasing particle diameters in accordance with themodel simulations. A model for the fluctuating particle velocity in turbulentgas-particle flow is derived using a set of stochastic differentialequations taking into account particle-particle collisions. Themodel shows that the particle fluctuating velocity increases whenparticle-particle collisions become more important and that increasingparticle response times reduces the fluctuating velocity. The modelcan also be used for an expansion of the deterministic model for theparticle kinetic energy.QC20100726
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Slater, Shane Anthony. "Particle transport in laminar and turbulent gas flows." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624527.
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Zhang, Yonghao. "Particle-gas interactions in two-fluid models of gas-solid flows." Thesis, University of Aberdeen, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367375.
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Modelling gas-solid two-phase flows using a two-fluid approach has two main difficulties: formulating constitutive laws for the particulate stresses and modelling the gas turbulence modulation. Due to the complex nature of the gas-particle interactions, there is no universal model covering every flow regime. In this thesis, three flow regimes with distinctive characteristics are studied, i.e. the very dense regime where the solid volume fraction, v2>5%, the dense flow regime where 5%≥1%, and the relatively dilute regime where 1%≥v2>0.1%. In the very dense flow regime, where the interstitial gas is normally neglected, the gas flow is assumed laminar and causes a viscous energy dissipation in the particulate phase. Numerical results for granular materials flowing down an inclined chute show that the interstitial gas may have a considerable effect in these flows. In the dense regime, where the inter-particle collisions are very important, a fluctuational energy transfer rate between the two phases is postulated, similar to that in a dilute Stokes flow. Consequently, the numerical solutions relax the restriction of elastic inter-particle collisions and show good agreement with experimental measurements. In the above two regimes, the kinetic theory of dry granular flow is adopted for the particulate stresses because the inter-particle collisions dominate the flows. The interstitial gas influence on the constitutive flow behaviour of the particulate phase is considered in the relatively dilute flow regime also, and a k-equation with a prescribed turbulent length scale is first used to address the gas turbulence modulation. Numerical results show that the gas turbulence has a significant effect on the microscopic flow behaviour of the particulate phase. The k-equation of Crowe & Gillandt (1998) has the best performance in predicting the experimentally observed phenomena. Finally, the influence of the particles on the k-Ε model coefficients are studied and the turbulent motion is considered to be restricted by the particles, thereby reducing the turbulent length scale directly. The simulation results indicate that these coefficients should be modified in order to incorporate the effect of particles.
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Yan, Fusheng Wood P. E. "Numerical study on turbulence modulation in gas-particle flows." *McMaster only, 2006.
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Strömgren, Tobias. "Modelling of turbulent gas-particle flow." Licentiate thesis, KTH, Mechanics, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4639.
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An Eulerian-Eulerian model for dilute gas-particle turbulent flows is
developed for engineering applications. The aim is to understand the effect of particles on turbulent flows. The model is implemented in a finite element code which is used to perform numerical simulations. The feedback from the particles on the turbulence and the mean flow of the gas in a vertical channel flow is studied. In particular, the influence of the particle response time and particle volume fraction on the preferential concentration of the particles near the walls, caused by the turbophoretic effect is explored. The study shows that the particle feedback decreases the accumulation of particles on the walls. It is also found that even a low particle volume fraction can have a significant impact on the turbulence and the mean flow of the gas. A model for the particle fluctuating velocity in turbulent gas-particle flow is derived using a set of stochastic differential
equations. Particle-particle collisions were taken into account. The model shows that the particle fluctuating velocity increases with increasing particle-particle collisions and that increasing particle response times decrease the fluctuating velocity.
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Liu, Xue. "Instability and segregation in bounded gas-particle and granular flows." Saarbrücken VDM Verlag Dr. Müller, 2006. http://d-nb.info/988937298/04.
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Liu, Xue. "Instability and segregation in bounded gas-particle and granular flows /." Saarbrücken : VDM Verlag Dr. Müller, 2008. http://d-nb.info/988937298/04.
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Tsui, Chak M. "A computational model for gas-particle flows with distributed phase interfaces." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ28819.pdf.
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Hodgson, Sarah M. "Turbulence modulation in gas-particle flows, a comparison of selected models." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0003/MQ46074.pdf.
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Tian, Zhaofeng, and rmit tian@gmail com. "Numerical Modelling of Turbulent Gas-Particle Flow and Its Applications." RMIT University. Aerospace, Mechanical and Manufacturing Engineering, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080528.150211.
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The aim of this thesis is three-fold: i) to investigate the performance of both the Eulerian-Lagrangian model and the Eulerian-Eulerian model to simulate the turbulent gas-particle flow; ii) to investigate the indoor airflows and contaminant particle flows using the Eulerian-Lagrangian model; iii) to develop and validate particle-wall collision models and a wall roughness model for the Eulerian-Lagrangian model and to utilize these models to investigate the effects of wall roughness on the particle flows. Firstly, the Eulerian-Lagrangian model in the software package FLUENT (FLUENT Inc.) and the Eulerian-Eulerian model in an in-house research code were employed to simulate the gas-particle flows. The validation against the measurement for two-phase flow over backward facing step and in a 90-degree bend revealed that both CFD approaches provide reasonably good prediction for both the gas and particle phases. Then, the Eulerian-Lagrangian model was employed to investigate the indoor airflows and contaminant particle concentration in two geometrically different rooms. For the first room configuration, the performances of three turbulence models for simulating indoor airflow were evaluated and validated against the measured air phase velocity data. All the three turbulence models provided good prediction of the air phase velocity, while the Large Eddy Simulation (LES) model base on the Renormalization Group theory (RNG) provided the best agreement with the measurements. As well, the RNG LES model is able to provide the instantaneous air velocity and turbulence that are required for the evaluation and design of the ventilation system. In the other two-zone ventilated room configuration, contaminant particle concentration decay within the room was simulated and validated against the experimental data using the RNG LES model together with the Lagrangian model. The numerical results revealed that the particle-wall coll ision model has a considerable effect on the particle concentration prediction in the room. This research culminates with the development and implementation of particle-wall collision models and a stochastic wall roughness model in the Eulerian-Lagrangian model. This Eulerian-Lagrangian model was therefore used to simulate the gas-particle flow over an in-line tube bank. The numerical predictions showed that the wall roughness has a considerable effect by altering the rebounding behaviours of the large particles and consequently affecting the particles motion downstream along the in-line tube bank and particle impact frequency on the tubes. Also, the results demonstrated that for the large particles the particle phase velocity fluctuations are not influenced by the gas-phase fluctuations, but are predominantly determined by the particle-wall collision. For small particles, the influence of particle-wall collisions on the particle fluctuations can be neglected. Then, the effects of wall roughness on the gas-particle flow in a two-dimensional 90-degree bend were investigated. It was found that the wa ll roughness considerably altered the rebounding behaviours of particles by significantly reducing the 'particle free zone' and smoothing the particle number density profiles. The particle mean velocities were reduced and the particle fluctuating velocities were increased when taking into consideration the wall roughness, since the wall roughness produced greater randomness in the particle rebound velocities and trajectories.
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Bell, Robyn Anne, and Robyn Bell@csiro au. "Numerical modelling of multi-particle flows in bubbling gas-solid fluidised beds." Swinburne University of Technology, 2000. http://adt.lib.swin.edu.au./public/adt-VSWT20050902.132803.
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In Victoria, Australia, brown coal is utilised as a major source of energy for the power generation industry. Victorian and South Australian brown coals have a very high moisture content and therefore, the efficiencies of power generation in traditional pulverised fuel fired furnaces are low. Fluidised beds offer a number of advantages over conventional furnaces, leading to improvements in efficiency and environmental impact. A disadvantage with implementing fluidised bed technology is the issue of scale-up. Fluidised bed behaviour can alter significantly with changes in scale, because of their strong dependence on the bed hydrodynamics. Hence, there is a need to accurately model bed behaviour to ensure that the effect of changes in scale are well understood and will not become costly and time consuming.
Computational Fluid Dynamics (CFD) techniques can be applied to fluidised bed systems to gain a better understanding of the hydrodynamic behaviour involved. In the past, numerical models have considered only single particle sizes due to the added complexity of interaction between particles of differing sizes and densities. Industrial fluidised beds typically contain more than one particle size and density, therefore there is a need to develop a numerical model which takes this into account. The aim of this thesis is to develop and validate CFD techniques for modelling the behavior of a gas-solid fluidised bed containing more than one particle size and density.
To provide validation data for the numerical model, physical experiments are undertaken on a small two-dimensional bubbling gas-solid fluidised bed. Mixing and segregation behaviour of different materials are investigated. The experiments demonstrate that whilst only a small proportion of the bed consists of different size/density particles, significant changes in bed behaviour are apparent. Changes in bubble rise velocity, bubble size and bubble shape are observed.
A number of constitutive equations must be included in the numerical model, including relationships for the momentum transfer between various phases and solids pressure. Different combinations of these constitutive equations are investigated. A new equation for particle-particle interactions is derived and included in a CFD model. The CFD model is validated against both data in the literature and physical experiments. From the validation studies, an optimum equation set is identified. This optimum equation set produces numerical results that closely resemble experimental bed behaviour, thus bringing the goal of solving scale-up problems one step closer. The use of this type of CFD model will ultimately result in timely and cost effective solutions for both the power generation and chemical processing industries.
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Healy, David Patrick. "On the full Lagrangian approach and thermophoretic deposition in gas-particle flows." Thesis, University of Cambridge, 2003. https://www.repository.cam.ac.uk/handle/1810/219497.
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Theoretical and experimental studies of particle deposition in turbulent pipe flow have been carried out for over forty years, but some of the most important transport mechanisms are still not well understood. The first part of this thesis is concerned with the calculation of particle density when using Lagrangian methods to predict inertial particle transport in two-dimensional laminar fluid flows. Traditionally, Lagrangian calculations involve integrating the particle equations of motion along particle pathlines, and the particle density is obtained by applying a statistical averaging procedure to those pathlines which intersect a particular computational grid cell. Unfortunately, extremely large numbers of particles are required to reduce the statistical errors to acceptable levels, and this makes the method computationally expensive. Recently, the Full Lagrangian approach has been developed, which allows the direct calculation of the particle density along particle pathlines. This method had previously been applied only to simple analytical flow fields. The application of the method to CFD generated fluid velocity fields was shown to be possible, and the results obtained using the Full Lagrangian approach were compared to those from a traditional Lagrangian approach. It was found that better quality solutions could be obtained with the use of far fewer particle pathlines. An analysis of the manner in which the Full Lagrangian approach deals with particles whose paths cross each other (and the resulting discontinuity in particle density) was also undertaken, and this illustrates the sophistication of the method. The second part of the thesis comprises an experimental and theoretical study of the deposition of small particles in turbulent flows by thermophoresis. Thermophoresis is the phenomenon whereby small particles suspended in a gas in which there exists a temperature gradient experience a force in the direction opposite from that of the temperature gradient. Previous researchers have attempted to impose a radial temperature difference in pipe flow experiments, but have not yet succeeded in attaining a constant thermophoretic force along the length of the pipe. This limits the accuracy and usefulness of the data for the validation of theoretical expressions for the thermophoretic fluxes. An experimental rig has been designed to achieve a constant thermophoretic force. This was done by using an annular geometry with a cold inner wall and hot outer wall. The particle size was varied and the deposition flux was measured for turbulent flow with three temperature differences. The deposition fluxes for small particles were found to be independent of dimensionless particle size, with each increase in temperature difference resulting in an increase in magnitude of the flux. Evidence of a thermophoresis-turbulence coupling was found for intermediate-sized particles, and large particles were not influenced by thermophoresis. A theory of particle deposition, developed for the case of turbulent pipe flow, was modified to study flow in a turbulent annulus, so that theoretical expressions for the thermophoretic fluxes could be included and compared with the experimental results. Agreement with experimental data was quite good, but some deficiencies in a widely used theoretical expression for the thermophoretic flux were exposed. An alternative expression was used, which gave much better agreement with the experimental data, and the mechanisms behind the thermophoresis-turbulence coupling were also investigated. The validation of this expression for the thermophoretic force will allow its inclusion in numerical studies of particle deposition in more complex geometries.
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Cardwell, Nicholas Don. "Investigation of Particle Trajectories for Wall Bounded Turbulent Two-Phase Flows." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/29642.
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The analysis of turbulent flows provides a unique scientific challenge whose solution remains central to unraveling the fundamental nature of all fluid dynamics. Measuring and predicting turbulent flows becomes even more difficult when considering a two-phase flow, which is a commonly encountered engineering problem across many disciplines. One such example, the ingestion of foreign debris into a gas turbine engine, provided the impetus for this study. Despite more than 40 years of research, operation with a particle-laden inlet flow remains a significant problem for modern turbomachines. The purpose, therefore, is to develop experimental methods for investigating multi-phase flows relevant to the cooling of gas turbine components.
Initially, several generic components representing turbine cooling designs were evaluated with a particle-laden flow using a special high temperature test facility. The results of this investigation revealed that blockage was highly sensitive to the carrier flowfield as defined by the cooling geometry. A second group of experiments were conducted in one commonly used cooling design using a Time Resolved Digital Particle Image Velocimetry (TRDPIV) system that directly investigated both the carrier flowfield and particle trajectories. Traditional PIV processing algorithms, however, were unable to resolve the particle motions of the two-phase flow with sufficient fidelity. To address this issue, a new Particle Tracking Velocimetry (PTV) algorithm was developed and validated for both single-phase and two-phase flows. The newly developed PTV algorithm was shown to outperform other published algorithms as well as possessing a unique ability to handle particle laden two-phase flows.
Overall, this work demonstrates several experimental methods that are well suited for the investigation of wall-bounded turbulent two-phase flows, with a special emphasis on a turbine cooling method. The studies contained herein provide valuable information regarding the previously unknown fluid and particle dynamics within the turbine cooling system.Ph. D.
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Park, Suhyeon. "Experimental Investigation of Flow and Wall Heat Transfer in an Optical Combustor for Reacting Swirl Flows." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/82349.
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The study of flow fields and heat transfer characteristics inside a gas turbine combustor provides one of the most serious challenges for gas turbine researchers because of the harsh environment at high temperatures. Design improvements of gas turbine combustors for higher efficiency, reduced pollutant emissions, safety and durability require better understanding of combustion in swirl flows and thermal energy transfer from the turbulent reacting flows to solid surfaces. Therefore, accurate measurement and prediction of the flows and heat loads are indispensable.
This dissertation presents flow details and wall heat flux measurements for reacting flow conditions in a model gas turbine combustor. The objective is to experimentally investigate the effects of combustor operating conditions on the reacting swirl flows and heat transfer on the liner wall. The results shows the behavior of swirling flows inside a combustor generated by an industrial lean pre-mixed, axial swirl fuel nozzle and associated heat loads.
Planar particle image velocimetry (PIV) data were analyzed to understand the characteristics of the flow field. Experiments were conducted with various air flow rates, equivalence ratios, pilot fuel split ratios, and inlet air temperatures. Methane and propane were used as fuel. Characterizing the impingement location on the liner, and the turbulent kinetic energy (TKE) distribution were a main part of the investigation. Proper orthogonal decomposition (POD) further analyzed the data to compare coherent structures in the reacting and non-reacting flows. Comparison between reacting and non-reacting flows yielded very striking differences. Self-similarity of the flow were observed at different operating conditions.
Flow temperature measurements with a thermocouple scanning probe setup revealed the temperature distribution and flow structure. Features of premixed swirl flame were observed in the measurement. Non-uniformity of flow temperature near liner wall was observed ranging from 1000 K to 1400 K. The results provide insights on the driving mechanism of convection heat transfer.
As a novel non-intrusive measurement technique for reacting flows, flame infrared radiation was measured with a thermographic camera. Features of the flame and swirl flow were observed from reconstructed map of measured IR radiation projection using Abel transformation. Flow structures in the infrared measurement agreed with observations of flame luminosity images and the temperature map. The effect of equivalence ratio on the IR radiation was observed.
Liner wall temperature and heat transfer were measured with infrared thermographic camera. The combustor was operated under reacting condition to test realistic heat load inside the industrial combustors. Using quartz glass liner and KG2 filter glass, the IR camera could measure inner wall surface temperature through the glass at high temperature. Time resolved axial distributions of inner/outer wall temperature were obtained, and hot side heat flux distribution was also calculated from time accurate solution of finite difference method.
The information about flows and wall heat transfer found in this work are beneficial for numerical simulations for optimized combustor cooling design. Measurement data of flow temperature, velocity field, infrared radiation, and heat transfer can be used as validation purpose or for direct inputs as boundary conditions. Time-independent location of peak location of liner wall temperature was found from time resolved wall temperature measurements and PIV flow measurements. This indicates the location where the cooling design should be able to compensate for the temperature increase in lean premixed swirl combustors.
The characteristics on the swirl flows found in this study points out that the reacting changes the flow structure significantly, while the operating conditions has minor effect on the structure. The limitation of non-reacting testing must be well considered for experimental combustor studies. However, reacting testing can be performed cost-effectively for reduced number of conditions, utilizing self-similar characteristics of the flows found in this study.Ph. D.
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Masson, Christian. "Numerical prediction of gas-solid particle flows over a wide range of concentration in irregular geometries." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=41710.
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The formulation of a co-located equal-order Control-Volume-based Finite Element Method (CVFEM) for the solution of two-fluid models of two-dimensional, planar or axisymmetric, incompressible, gas-solid particle flows is presented in this thesis. The main focus is on the development of a numerical method that allows computer simulation of gas-solid particle flows over a wide range of solid-phase volume concentration in complex irregular geometries.A general two-fluid mathematical model is presented. This model is essentially borrowed from published works in the area of granular flows. It is established here that this model is applicable to gas-solid flows over a wide range of solid-phase concentration. The governing equations of the fluid phase are obtained by volume averaging the Navier-Stokes equations for an incompressible fluid. The solid-phase macroscopic equations are derived using an approach that has been successfully used earlier for the description of granular materials, and is based on the kinetic theory of dense gases. This approach accounts for particle/particle collisions, and permits the determination of the solid-phase macroscopic properties such as viscosity and pressure.
The proposed CVFEM is formulated by borrowing and extending ideas put forward in earlier CVFEMs for single-phase flows. In axisymmetric problems, the calculation domain is discretized into torus-shaped elements and control volumes: in a longitudinal cross-sectional plane, or in planar problems, these elements are three-node triangles, and the control volumes are polygons obtained by joining the centroids of the three-node triangles to the midpoints of the sides. In each element, mass-weighted skew upwind functions are used to interpolate the volume concentrations. An iterative variable adjustment algorithm is used to solve the discretized equations.
The chosen mathematical model, along with its specializations to single-phase flows and dilute gas-solid flows, and the proposed CVFEM have been applied to several test problems and some demonstration problems. These test and demonstration problems include single-phase flows, dilute-concentration gas-solid particle flows and dense-concentration gas-solid particle flows. The CVFEM results have been compared with results of independent numerical and experimental investigations whenever possible. These comparisons and the results of the demonstration problems are quite encouraging.
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Niaki, Seyed Reza Amini. "Effects of inter particle friction on the meso-scale hydrodynamics of dense gas-solid fluidized flows." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/18/18147/tde-10122018-165927/.
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Gas-solid fluidized bed reactors are widely applied in chemical and energy industries, and their design and scale-up are virtually empirical, extremely expensive and time consuming. This scenario has motivated the development of alternative theoretical tools, and two-fluid modeling, where gas and particulate are both treated as interpenetrating continuum phases, has appeared as a most promising approach. Owing to the large domains to be resolved in real-scale fluidized bed reactors, only filtered modeling approaches are feasible, and closure models become necessary to recover sub-grid effects that are filtered by the very coarse numerical grids that are imposed owing to computational limitations. Those closure models, which in hydrodynamic formulations account for filtered interphase momentum exchanges and filtered and residual stresses in the phases, can be derived from results of highly resolved simulations (HRS) performed over small size domains under refined numerical grids. One widely practiced approach consists of applying two-fluid modeling under micro-scale defined closures, generally known as microscopic two-fluid modeling. This approach includes microscopic closures for solid phase stresses derived from the kinetic theory of granular flows (KTGF), which accounts for kinetic-collisional effects only, and is adequate to dilute flows. Otherwise, the conventional KTGF does not account for interparticle friction effects, and its application to dense flow conditions is quite questionable. In this work a literature available modified version of KTGF is applied which also accounts for interparticle friction, and highly resolved simulations are performed for dense flow conditions in order to evaluate the effects of friction over relevant filtered parameters (namely effective drag coefficient, filtered and residual stresses). Ranges of domain average solid volume fractions and gas Reynolds numbers are considered (macro-scale conditions) embracing dense gas-solid fluidized flows from suspensions up to pneumatic transport. The MFIX open source code is used in all the simulations, which are performed over 2D periodical domains for a unique monodisperse particulate. The HRS results (i.e. meso-scale flow fields) are filtered over regions compatible with grid sizes in large scale simulations, and the relevant filtered parameters of concern are derived and classified by ranges of other filtered parameters taken as independent variables (filtered solid volume fraction, filtered slip velocity, and filtered kinetic energy of solid velocity fluctuations, which are referred to as markers). Results show that the relevant filtered parameters of concern are well correlated to all of those filtered markers, and also to all of the imposed macro-scale conditions. Otherwise, interparticle friction showed no significant effects over any filtered parameter. It is recognized that this issue clearly requires further investigation notably regarding the suitability of the markers that were assumed for classifying the filtered results. The current work is intended as a contribution for future developments of more accurate closure models for large scale simulations of gas-solid fluidized flows.Reatores de leito fluidizado de escoamento gás-sólido são largamente utilizados nas indústrias química e de energia, e o seu projeto e escalonamento são virtualmente empíricos, extremamente caros e demorados. Este cenário tem motivado o desenvolvimento de ferramentas teóricas alternativas, e a modelagem de dois fluidos, onde gás e particulado são ambos tratados com fases contínuas interpenetrantes, tem surgido como uma aproximação muito promissora. Devido aos grandes domínios a serem resolvidos em reatores de leito fluidizado de escala real, apenas aproximações de modelagem filtradas são viáveis, e modelos de fechamento tornam-se necessários para recuperar efeitos sub-malha que são filtrados pelas malhas numéricas grosseiras que são impostas devido as limitações computacionais. Estes modelos de fechamento, que em formulações hidrodinâmicas respondem principalmente por trocas de momentum filtradas entre fases e tensões filtradas e residuais nas fases, podem ser obtidos de resultados de simulações altamente resolvidas (SAR) realizadas em domínios de dimensões reduzidas sob malhas numéricas refinadas. Uma aproximação largamente praticada consiste na aplicação de modelagem de dois fluidos sob fechamentos definidos na micro-escala, genericamente conhecida como modelagem microscópica de dois fluidos. Esta aproximação inclui fechamentos microscópicos para tensões da fase sólida obtidos da teoria cinética dos escoamentos granulares (TCEG), que considera apenas efeitos cinéticos-colisionais, e é adequada para escoamentos diluídos. Por outro lado, a TCEG convencional não leva em conta efeitos de fricção interpartículas, e sua aplicação para condições densas de escoamento é bastante questionável. Neste trabalho aplica-se uma versão modificada da TCEG disponível na literatura que também leva em conta fricção interpartículas, e simulações altamente resolvidas são realizadas para condições de escoamentos densos visando avaliar os efeitos da fricção sobre os parâmetros filtrados relevantes (coeficiente de arrasto efetivo, tensões filtradas e residuais). Considera-se faixas de frações volumétricas de sólido e números de Reynolds do gás médios no domínio (condições de macro-escala) abrangendo escoamentos gás-sólido fluidizados densos desde suspensões até transporte pneumático. O código aberto MFIX é utilizado em todas as simulações, que foram executadas sobre domínios periódicos 2D para um único particulado monodisperso. Os resultados das SAR (i.e., campos de escoamento de meso-escala) foram filtrados sobre regiões compatíveis com tamanhos de malha praticados em simulações de grandes escalas, e os parâmetros filtrados relevantes de interesse são calculados e classificados por faixas de outros parâmetros filtrados tomados como variáveis independentes (fração volumétrica de sólido filtrada, velocidade de deslizamento filtrada, e energia cinética das flutuações de velocidade da fase sólida filtrada, que são referidos como marcadores). Os resultados mostram que os parâmetros filtrados relevantes de interesse são bem correlacionados com todos os marcadores, e também com todas as condições de macro-escala impostas. Por outro lado, a fricção interpartículas não mostrou efeitos significativos sobre qualquer parâmetro filtrado. Reconhece-se que este aspecto claramente requer investigações adicionais, notadamente com respeito à adequação dos marcadores que foram considerados para classificação dos resultados filtrados. O trabalho corrente é posto como uma contribuição para o desenvolvimento futuro de modelos de fechamento mais acurados para simulações de grandes escalas de escoamentos gás-sólido fluidizados.
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Pachler, Klaus, Thomas Frank, and Klaus Bernert. "Simulation of Unsteady Gas-Particle Flows including Two-way and Four-way Coupling on a MIMD Computer Architectur." Universitätsbibliothek Chemnitz, 2002. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-200200352.
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The transport or the separation of solid particles or droplets suspended in a fluid flow is a common task in mechanical and process engineering. To improve machinery and physical processes (e.g. for coal combustion, reduction of NO_x and soot) an optimization of complex phenomena by simulation applying the fundamental conservation equations is required. Fluid-particle flows are characterized by the ratio of density of the two phases gamma=rho_P/rho_F, by the Stokes number St=tau_P/tau_F and by the loading in terms of void and mass fraction.
Those numbers (Stokes number, gamma) define the flow regime and which relevant forces are acting on the particle. Dependent on the geometrical configuration the particle-wall interaction might have a heavy impact on the mean flow structure. The occurrence of particle-particle collisions becomes also more and more important with the increase of the local void fraction of the particulate phase. With increase of the particle loading the interaction with the fluid phase can not been neglected and 2-way or even 4-way coupling between the continous and disperse phases has to be taken into account.
For dilute to moderate dense particle flows the Euler-Lagrange method is capable to resolve the main flow mechanism. An accurate computation needs unfortunately a high number of numerical particles (1,...,10^7) to get the reliable statistics for the underlying modelling correlations. Due to the fact that a Lagrangian algorithm cannot be vectorized for complex meshes the only way to finish those simulations in a reasonable time is the parallization applying the message passing paradigma.
Frank et al. describes the basic ideas for a parallel Eulererian-Lagrangian solver, which uses multigrid for acceleration of the flow equations. The performance figures are quite good, though only steady problems are tackled. The presented paper is aimed to the numerical prediction of time-dependend fluid-particle flows using the simultanous particle tracking approach based on the Eulerian-Lagrangian and the particle-source-in-cell (PSI-Cell) approach. It is shown in the paper that for the unsteady flow prediction efficiency and load balancing of the parallel numerical simulation is an even more pronounced problem in comparison with the steady flow calculations, because the time steps for the time integration along one particle trajectory are very small per one time step of fluid flow integration and so the floating point workload on a single processor node is usualy rather low.
Much time is spent for communication and waiting time of the processors, because for cold flow particle convection not very extensive calculations are necessary. One remedy might be a highspeed switch like Myrinet or Dolphin PCI/SCI (500 MByte/s), which could balance the relative high floating point performance of INTEL PIII processors and the weak capacity of the Fast-Ethernet communication network (100 Mbit/s) of the Chemnitz Linux Cluster (CLIC) used for the presented calculations. Corresponding to the discussed examples calculation times and parallel performance will be presented. Another point is the communication of many small packages, which should be summed up to bigger messages, because each message requires a startup time independently of its size. Summarising the potential of such a parallel algorithm, it will be shown that a Beowulf-type cluster computer is a highly competitve alternative to the classical main frame computer for the investigated Eulerian-Lagrangian simultanous particle tracking approach.
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Bello, Oladele O. [Verfasser]. "Modelling particle transport in gas oil sand multiphase flows and its applications to production operations / submitted by Oladele O. Bello." [Clausthal-Zellerfeld] : [Univ.-Bibliothek], 2008. http://d-nb.info/990729931/34.
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Klinkov, Konstantin V. "Unsteady gas flows and particle dynamics in the shock layer formed by the impingement of a supersonic two-phase jet onto a plate /." Köln : DLR, Abt. Unternehmensorganisation und -information, 2005. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=014177140&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Perkins, Hugh Douglas. "Development and Demonstration of a Computational Tool for the Analysis of Particle Vitiation Effects in Hypersonic Propulsion Test Facilities." Case Western Reserve University School of Graduate Studies / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1227553721.
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Du, Sart Colin F. "Design and prototyping of a test facility to investigate the transport properties of dilute phase gas-particle flows applicable to coal-fired power plants." Master's thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/24889.
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Understanding the properties of dilute phase gas-particle transport and the applicability of the different empirical correlations found in literature for these properties are crucial in the study of Pulverized Fuel conveying applicable to South African coal-fired power plants. Having access to a test facility in which empirical data can be generated under controlled operating conditions would enhance this understanding and will allow more informed application of these correlations. The aim of this thesis was to develop a concept design and prototype of a pneumatic conveying test facility that can be used to evaluate these empirical correlations and property relationships. A comprehensive literature review was conducted of the empirical correlations available and a study was conducted to determine the scaling required to achieve similarity. A theoretical process model was also developed together with a methodology to determine the operating envelope of the blower. The model and methodology were subsequently used in the design of a prototype test facility that would demonstrate the critical particle feed and extraction processes, and to derive suitable specifications for the blower. The prototype, including a complete data acquisition and control system, was developed, constructed and commissioned in cooperation with a commercial engineering company. The facility allows for the control, online measurement and recording of the gas and particle mass flow rates. Practical tests were then conducted with Fly Ash, as a substitute for Pulverized Coal, to demonstrate the particle feed and extraction processes and to evaluate the accuracy of control of the gas and particle mass flow rates. Tests were conducted for loadings (particle to gas mass flow ratios) between 0.988 and 6.860 at gas mass flow rates between 0.051 and 0.115kg/s and particle mass flow rates between 0.077 and 0.600kg/s. A methodology to determine the particle mass flow rate and its associated uncertainty from the Loss In Weight and Gain In Weight systems was developed from basic principles and demonstrated. The relative uncertainties calculated for the measured particle mass flow rates are less than ±1% for all tests. The maximum relative uncertainties calculated for the measured gas mass flow rates and loadings are ±6%. The conceptual overall system layout for the final test facility, including the instrumentation design, was then refined based on the experience gained and recommendations are made for consideration in the detail design. The conceptual design allows for the control of the gas and particle mass flow rates as well as the gas temperature and pressure level. The final test facility will be suitable to conduct pressure drop tests, saltation and choking tests, as well as mass balances and visual observations. The process model and methodologies developed here may now be applied in the detail design and operation of such a final test facility.
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Gnanaselvam, Pritheesh. "Modeling Turbulent Dispersion and Deposition of Airborne Particles in High Temperature Pipe Flows." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1598016744932462.
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Klinkov, Konstantin [Verfasser], Dirk [Akademischer Betreuer] Ronneberger, and Martin [Akademischer Betreuer] Rein. "Unsteady gas flows and particle dynamics in the shock layer formed by the impingement of a supersonic two-phase jet onto a plate / Konstantin Klinkov. Gutachter: Martin Rein. Betreuer: Dirk Ronneberger." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2005. http://d-nb.info/1042971676/34.
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Klinkov, Konstantin V. [Verfasser], Dirk [Akademischer Betreuer] Ronneberger, and Martin [Akademischer Betreuer] Rein. "Unsteady gas flows and particle dynamics in the shock layer formed by the impingement of a supersonic two-phase jet onto a plate / Konstantin Klinkov. Gutachter: Martin Rein. Betreuer: Dirk Ronneberger." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2005. http://nbn-resolving.de/urn:nbn:de:gbv:7-webdoc-25-7.
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Weit, Anne. "Etude expérimentale de la concentration de particules solides dans les écoulements volcaniques biphasés turbulents." Thesis, Université Clermont Auvergne (2017-2020), 2018. http://www.theses.fr/2018CLFAC060.
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Des mélanges de gaz et de particules sont présents dans divers environnements géophysiques. De tels mélanges chauds sont générés par des éruptions volcaniques explosives et comprennent des écoulements de conduit, des jets et des panaches, ainsi que des courants de densité pyroclastiques. La concentration de particules dans ces mélanges volcaniques peut varier fortement, allant de concentrations élevées (>50 % en volume) dans les écoulements denses fluidisés à des concentrations très faibles dans les suspensions diluées dans lesquelles les particules sont mises en suspension par la phase gazeuse turbulente. Une limite de concentration inférieure à ~% en volume dans les suspensions diluées a été suggérée par des études récentes, car des concentrations plus élevées nécessiteraient une énergie cinétique turbulente excessive. L'objectif principal de cette thèse est d'étudier expérimentalement le comportement d'un écoulement d'air turbulent dans un cylindre avec des concentrations de particules croissantes, pour différents nombres de Reynolds et en utilisant différents types de particules. Les nombres de Reynolds des mélanges gaz-particules dans les expériences atteignaient ~106. Une première série d'expériences a été menée avec des billes de verre de différentes tailles allant de 75-80 μm jusqu'à 2 mm, pour un total de huit tailles de particules. Au-dessus d'un seuil de concentration moyenne de 0.5-3 % en volume, qui augmentait avec le nombre de Reynolds, le comportement de l'écoulement a montré une transition d'une suspension homogène de particules (sous la concentration maximale) vers une séparation en une partie basale dense et une partie supérieure diluée contenant la concentration maximale des particules. Ce seuil de concentration a été détecté à l'aide de mesures de pression et d'une méthode impliquant une sphère dont la densité était légèrement inférieure à la densité apparente des particules et qui pouvait donc flotter au-dessus de la partie basale dense, si celle-ci était présente. Des vidéos à haute vitesse ont révélé que l'apparition de la concentration maximale de particules coïncidait avec l'émergence d’amas de particules dans la partie turbulente diluée. Dans une deuxième partie de la thèse, les expériences ont été répétées pour cinq gammes de tailles de particules de céramique et elles ont révélé le même comportement général que pour les billes de verre. Pour les deux types de particules, une concentration maximale a pu être détectée pour presque toutes les tailles de particules et a montré une augmentation avec le nombre de Reynolds à la puissance 1/5 (billes de verre) ou 0.4 (billes de céramique). Compte tenu du nombre de Reynolds des particules, la concentration maximale des particules augmente ensuite jusqu'à la puissance de 1/6 pour les particules de céramique et de verre. Ces résultats ouvrent de nouvelles perspectives sur la structure des mélanges gaz-particules volcaniques et ils fournissent également des contraintes pour les données d'entrée et de sortie des simulations numériques et pour les observations géophysiquesMixtures consisting of gas and particles can be found in various geophysical environments. Hot mixtures are generated by explosive volcanic eruptions and include conduit flows, jets and buoyant plumes, and pyroclastic density currents. The particle concentration within these volcanic mixtures can vary highly, from high concentrations (>50 vol. %) in dense fluidized flows to very low concentrations in dilute suspensions in which the particles are suspended by the turbulent gas phase. A concentration limit of less than ~1 vol. % in dilute suspensions was suggested by recent studies, as higher concentrations would require excessive turbulent kinetic energy. The main objective of this thesis was to investigate experimentally the behavior of a turbulent air flow in a pipe with increasing particle concentrations, for different Reynolds numbers and using different types of particles. The Reynolds numbers of the gas-particle mixtures in the experiments were up to ~106. A first set of experiments was conducted with glass beads of varying sizes from 75-80 μm up to 2 mm, for eight particle size ranges in total. Above a bulk concentration threshold of ~0.5-3 vol. %, which increased with the Reynolds number, the flow behavior changed from a homogeneous suspension of particles (below the maximum concentration) to a separation into a dense basal part and an upper dilute part carrying the maximum concentration of particles. This concentration threshold was detected with pressure measurements and a method that involved a ball of a slightly lower density than the bulk density of the particles, which could thus float over the dense basal part, if present. High-speed videos revealed that the occurrence of the maximum particle concentration coincided with the emergence of particle clusters in the dilute turbulent part. In a second part of the thesis, the experiments were repeated for five ceramic particle size ranges and they yielded the same general behavior as for the glass beads. For both types of particles, a maximum concentration could be detected for almost all particle size ranges and showed an increase with the mixture Reynolds number to the power 1/5 (glass beads) or 0.4 (ceramic beads). Considering the particle Reynolds number the maximum particle concentration then increase to the power 1/6 for both ceramic and glass particles. These results give new insights about the structure of volcanic gas-particle mixtures and they also provide constraints for input and output data of numerical simulations and for geophysical observations
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Keita, Sana. "Eulerian Droplet Models: Mathematical Analysis, Improvement and Applications." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37907.
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The Eulerian description of dispersed two-phase flows results in a system of
partial differential equations describing characteristics of the flow, namely volume
fraction, density and velocity of the two phases, around any point in space over
time. When pressure forces are neglected or a same pressure is considered for both
phases, the resulting system is weakly hyperbolic and solutions may exhibit vacuum
states (regions void of the dispersed phase) or localized unbounded singularities (delta shocks) that are not physically desirable. Therefore, it is crucial to find a physical way for preventing the formation of such undesirable solutions in weakly hyperbolic Eulerian two-phase flow models.
This thesis focuses on the mathematical analysis of an Eulerian model for air-
droplet flows, here called the Eulerian droplet model. This model can be seen as the
sticky particle system with a source term and is successfully used for the prediction
of droplet impingement and more recently for the prediction of particle flows in air-
ways. However, this model includes only one-way momentum exchange coupling, and develops delta shocks and vacuum states. The main goal of this thesis is to improve this model, especially for the prevention of delta shocks and vacuum states, and the adjunction of two-way momentum exchange coupling. Using a characteristic analysis, the condition for loss of regularity of smooth solutions of the inviscid Burgers
equation with a source term is established. The same condition applies to the droplet
model. The Riemann problems associated, respectively, to the Burgers equation with
a source term and the droplet model are solved. The characteristics are curves that
tend asymptotically to straight lines. The existence of an entropic solution to the
generalized Rankine-Hugoniot conditions is proven. Next, a way for preventing the
formation of delta shocks and vacuum states in the model is identified and a new
Eulerian droplet model is proposed. A new hierarchy of two-way coupling Eulerian
models is derived. Each model is analyzed and numerical comparisons of the models
are carried out. Finally, 2D computations of air-particle flows comparing the new
Eulerian droplet model with the standard Eulerian droplet model are presented.
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Nerisson, Philippe. "Modélisation du transfert des aérosols dans un local ventilé." Thesis, Toulouse, INPT, 2009. http://www.theses.fr/2009INPT001H/document.
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La protection des opérateurs et la surveillance des ambiances de travail en cas de mise en suspension d’aérosols radioactifs, dans un local ventilé d’une installation nucléaire, requièrent la connaissance de l’évolution spatio-temporelle de la concentration en particules, en tout point du local considéré. L’estimation précise de cette concentration a fait l’objet du développement de modèles spécifiques de transport et de dépôt d’aérosols dans un local ventilé, dans le cadre d’une thèse cofinancée par l’IRSN et EDF, en collaboration avec l’IMFT. Un formalisme eulérien de glissement est utilisé pour modéliser le transport des aérosols. Celui-ci est basé sur une unique équation de transport des concentrations en particules (« Diffusion-Inertia model »). L’étude spécifique du dépôt d’aérosols en parois a permis de développer un modèle de couche limite, qui consiste à déterminer précisément le flux de dépôt de particules en parois, quels que soient le régime de dépôt et l’orientation de la surface considérée. Les modèles de transport et de dépôt finalement retenus ont été implantés dans Code_Saturne, un logiciel de mécanique des fluides. La validation de ces modèles a été effectuée à partir de données de la littérature en géométries simples, puis sur la base de campagnes expérimentales de traçage dans des locaux ventilés d’environ 30 m³ et 1500 m³When particulate radioactive contamination is likely to become airborne in a ventilated room, assessment of aerosol concentration in every point of this room is important, in order to ensure protection of operators and supervision of workspaces. Thus, a model of aerosol transport and deposition has been developed as part of a project started with IRSN, EDF and IMFT. A simplified eulerian model, called “diffusion-inertia model” is used for particle transport. It contains a single transport equation of aerosol concentration. The specific study of deposition on walls has permitted to develop a boundary condition approach, which determines precisely the particle flux towards the wall in the boundary layer, for any deposition regime and surface orientation.The final transport and deposition models retained have been implemented in a CFD code called Code_Saturne. These models have been validated according to literature data in simple geometries and tracing experiments in ventilated rooms, which have been carried out in 30 m³ and 1500 m³ laboratory rooms
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Strömgren, Tobias. "Modelling of turbulent gas-particle flow /." Stockholm : Mekanik, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4639.
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Gai, Guodong. "Modeling of water sprays effects on premixed hydrogen-air explosion, turbulence and shock waves Modeling pressure loads during a premixed hydrogen combustion in the presence of water spray Numerical study on laminar flame velocity of hydrogen-air combustion under water spray effects Modeling of particle cloud dispersion in compressible gas flows with shock waves A new formulation of a spray dispersion model for particle/droplet-laden flows subjected to shock waves Particles-induced turbulence: a critical review of physical concepts, numerical modelings and experimental investigation A new methodology for modeling turbulence induced 1 by a particle-laden flow using a mechanistic model." Thesis, Normandie, 2020. http://www.theses.fr/2020NORMIR14.
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Cette thèse de doctorat est dédiée au développement de modèles physiques pour l’étude des systèmes d’aspersion de gouttelettes d’eau en milieu réactif d’hydrogène-air pré-mélangée dans les centrales nucléaires. Des modèles d’ordre réduit sont développés pour décrire l’évaporation des gouttelettes d’eau dans la flamme, la dispersion des nuages de particules après le passage des ondes de choc et l’évolution de l’échelle caractéristiques de turbulence avec la présence d’un jet d’eau. Une nouvelle méthodologie est proposée pour évaluer les effets de l’évaporation par l’aspersion sur la propagation de la flamme d’hydrogène turbulente à l’intérieur d’un volume fermé et un modèle simple est développé pour la quantification de la décélération de la vitesse laminaire avec l’évaporation des gouttelettes à l’intérieur de la flamme. Également, un modèle analytique est proposé pour la prédiction de la dispersion de nuage de particule après le passage d’une onde de choc en s’appuyant sur le one-way formalisme avec une extension afin de prédire l’apparition d’un pic de densité du nombre de particules en utilisant le two-way formalisme. En ce qui concerne la modulation de la turbulence induite par les particules, un modèle simple est utilisé pour l’estimation des échelles intégrales de la turbulence induites par l’injection de nuage des particules. Ces modèles numériques développés peuvent être couplés pour être mis en œuvre dans les simulations numériques à grande échelle de l’effet du système d’aspersion sur les explosions accidentelles d’hydrogène dans les centrales nucléairesThis PhD dissertation is dedicated to develop simple models to investigate the effect of water spray system on the premixed hydrogen-air combustion in the nuclear power plants. Specific simple models are developed to describe the water droplet evaporation in the flame, particle cloud dispersion after the shock wave passage, and turbulence length scale evolution with the presence of a water spray. A methodology is proposed to evaluate the spray evaporation effects on the propagation of the turbulent hydrogen flame inside a closed volume and a simple model is developed for the quantification of the laminar velocity deceleration with the droplets evaporation inside the flame. An analytical model is proposed for the prediction of particle cloud dispersion after the shock passage in the one-way formalism and another analytical model is dedicated to describe the spray-shock interaction mechanism and predict the appearance of a particle number density peak using the two-way formalism. A review of the important criteria and physical modelings related to the particle-induced turbulence modulation is given and a mechanistic model is used for the estimation of the turbulent integral length scales induced by the injection of particle clouds. These developed numerical models can be coupled to implement in the large-scale numerical simulations of the spray system effects on the accidental hydrogen explosions in the nuclear power plants
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Roveda, Roberto. "A combined discrete velocity particle based numerical approach for continuum/rarefied flows /." Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004370.
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Hollis, David. "Particle image velocimetry in gas turbine combustor flow fields." Thesis, Loughborough University, 2004. https://dspace.lboro.ac.uk/2134/7640.
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Current and future legislation demands ever decreasing levels of pollution from gas turbine engines, and with combustor performance playing a critical role in resultant emissions, a need exists to develop a greater appreciation of the fundamental causes of unsteadiness. Particle Image Velocimetry (PIV) provides a platform to enable such investigations. This thesis presents the development of PIV measurement methodologies for highly turbulent flows. An appraisal of these techniques applied to gas turbine combustors is then given, finally allowing a description of the increased understanding of the underlying fluid dynamic processes within combustors to be provided. Through the development of best practice optimisation procedures and correction techniques for the effects of sub-grid filtering, high quality PN data has been obtained. Time average statistical data at high spatial resolution has been collected and presented for generic and actual combustor geometry providing detailed validation of the turbulence correction methods developed, validation data for computational studies, and increased understanding of flow mechanisms. These data include information not previously available such as turbulent length scales. Methodologies developed for the analysis of instantaneous PIV data have also allowed the identification of transient flow structures not seen previously because they are invisible in the time average. Application of a new `PDF conditioning' technique has aided the explanation of calculated correlation functions: for example, bimodal primary zone recirculation behaviour and jet misalignments were explained using these techniques. Decomposition of the velocity fields has also identified structures present such as jet shear layer vortices, and through-port swirling motion. All of these phenomena are potentially degrading to combustor performance and may result in flame instability, incomplete combustion, increased noise and increased emissions.
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Forsyth, Peter. "High temperature particle deposition with gas turbine applications." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:61556237-feed-43cb-9f4a-d0aed00ca3f8.
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This thesis describes validated improvements in the modelling of micron-sized particle deposition within gas turbine engine secondary air systems. The initial aim of the research was to employ appropriate models of instantaneous turbulent flow behaviour to RANS CFD simulations, allowing the trajectory of solid particulates in the flow to be accurately predicted. Following critical assessment of turbophoretic models, the continuous random walk (CRW) model was chosen to predict instantaneous fluid fluctuating velocities. Particle flow, characterised by non-dimensional deposition velocity and particle relaxation time, was observed to match published experimental vertical pipe flow data. This was possible due to redefining the integration time step in terms of Kolmagorov and Lagrangian time scales, reducing the disparity between simulations and experimental data by an order of magnitude. As no high temperature validation data for the CRW model were available, an experimental rig was developed to conduct horizontal pipe flow experiments under engine realistic conditions. Both the experimental rig, and a new particulate concentration measurement technique, based on post test aqueous solution electrical conductivity, were qualified at ambient conditions. These new experimental data compare well to published data at non-dimensional particle relaxation times below 7. Above, a tail off in the deposition rate is observed, potentially caused by a bounce or shear removal mechanism at higher particle kinetic energy. At elevated temperatures and isothermal conditions, similar behaviour is observed to the ambient data. Under engine representative thermophoretic conditions, a negative gas to wall temperature gradient is seen to increase deposition by up to 4.8 times, the reverse decreasing deposition by a factor of up to 560 relative to the isothermal data. Numerical simulations using the CRW model under-predict isothermal deposition, though capturing relative thermophoretic effects well. By applying an anisotropic Lagrangian time scale, and cross trajectory effects of the external gravitational force, good agreement was observed, the first inclusion of the effect within the CRW model. A dynamic mesh morphing method was then developed, enabling the effect of large scale particle deposition to be included in simulations, without continual remeshing of the fluid domain. Simulation of an impingement jet array showed deposition of characteristic mounds up to 30% of the hole diameter in height. Simulation of a passage with film-cooling hole off-takes generated hole blockage of up to 40%. These cases confirmed that the use of the CRW generated deposition locations in line with scant available experimental data, but widespread airline fleet experience. Changing rates of deposition were observed with the evolution of the deposits in both cases, highlighting the importance of capturing changing passage geometry through dynamic mesh morphing. The level of deposition observed, was however, greater than expected in a real engine environment and identifies a need to further refine bounce-stick and erosion modelling to complement the improved prediction of impact location identified in this thesis.
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Naylor, Michael J. "Fluid flow and particle size in gas atomization for fine powders." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/47415.
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Zhang, Ming. "Optical measurement of ash particle size and velocity in gas-solid flow." Morgantown, W. Va. : [West Virginia University Libraries], 2004. https://etd.wvu.edu/etd/controller.jsp?moduleName=documentdata&jsp%5FetdId=3462.
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Thesis (M.S.)--West Virginia University, 2004.Title from document title page. Document formatted into pages; contains x, 98 p. : ill. (some col.) + 1 video file. Includes a video file (29 sec.). Includes abstract. Includes bibliographical references (p. 91-92).
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Woiski, Emanuel Rocha. "Solutions of the kinetic coagulation equation and predictions for gas-particle flow." Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47310.
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Mathisen, Anette. "An Experimental and Computational Investigation of Gas/Particle Flow in a Vertical Lifter." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-11267.
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Experimental and computational investigations of dilute gas/particle flow in a vertical lifter are performed. The effect of superficial gas velocity, particle density, particle size distribution and particle loading on particle velocities, particle fluctuations and particle cross-moment have been studied experimentally using laser Doppler anemometry (LDA) and particle image velocimetry (PIV). The results from the experimental investigation is compared with the computational investigation using FluentR. The experimental measurements are performed on a lab-scale vertical lifter, consisting of a fluidizing silo and a receiving tank with a glass pipe in which the solids phase is transported. The particles are placed in the fluidization tank and transport air enters at the bottom of the silo. The transport pipe is suspended above the inlet and as the transport air passes the opening, the particles are dragged into the air flow and transported upwards to the receiving tank. Fluidizing air is used to control the particle loading in the system and supplied through a distribution plate. The test section of the transport pipe is made of glass to enable the use of the optical laser based investigation techniques, LDA and PIV. Two types of powders are used, ZrO2 and glass, each with two different particle size distributions, average diameter of 260 and 530 micron and 120 and 518 micron, respectively. The experimental techniques LDA and PIV are used to investigate a dilute gas/particle vertical flow. The two techniques are also evaluated for use on this type of flow. LDA is a single point measurement technique, which means that one point is measured at a time. The acquisition stops when a pre-set criteria is reached, this can either be based on sample number or time. A measurement spanning over the whole cross-section of the pipe consists of several points. These points makes up a cross-sectional profile. PIV on the other hand is a whole field technique and consequently the whole cross-section of the pipe is measured simultaneously. Within a given time interval two laser pulses light up the flow and the reflection of the particles is captured by a camera. Satisfactory measurements of all the particle types are performed using LDA. The mean axial and normal particle velocities and fluctuations as well as the cross-moment, are measured at varying particle volume fraction and superficial gas velocity. The value of the measured quantities will vary depending on the particle size, particle density, particle volume fraction and superficial gas velocity. A comparison between the particle types show that the mean axial particle velocity is highest for the lighter and smaller particles, but the fluctuations are greatest for the larger and heavier particles. For smaller particles LDA is a very efficient measurement tool. For the largest particles the acquisition can be time consuming due to relatively few particles in the system. PIV measurements are generally performed satisfactory on all of the particle types. The exception is measurements performed on the smaller particles at the higher particle volume fractions. The mean axial and normal particle velocities and fluctuations including the crossmoments are measured at varying particle volume fraction and superficial gas velocity. The results from the measurements show that the measured quantities will vary depending on the particle size, particle density, particle volume fraction and superficial gas velocity. When comparing the particle types, it is observed that the mean axial particle velocity is highest for the smaller and lighter particles while the fluctuations are lower than for the larger and heavier ones. The combination of particles larger than commonly used tracer particles and higher particle volume fractions is challenging, but overall the PIV technique works well. Comparison between LDA and PIV results show generally a good agreement for the mean axial particle velocity. The mean axial and normal particle fluctuations and the particle crossmoment are generally measured lower when using PIV. Simulations are performed using FluentR and the model Euler-Euler, where both phases are regarded as being continua. The kinetic theory of granular flow (KTGF) is included for the solids phase. Initially only the single transport pipe is simulated in 2d and 3d. The flow in this pipe is dilute and therefore the simulations which included KTGF and the Gidaspow drag model are compared to simulations enabling the constant viscosity model (CVM) and the Schiller-Naumann drag model. The results from the simulations show very little difference between the two simulations. Euler-Euler with KTGF 2d and 3d simulations are performed for all of the particle types. Little difference between 2d and 3d simulations are observed. A comparison between simulations and experimental results, LDA and PIV, showed good agreement for axial particle velocity for all of the particle types. The upward transport of particles in a vertical pipe is also simulated using Euler-Lagrange. Here a number of particles are tracked and compared to the experiments with good agreement. Simulations of the vertical lifter, a silo containing the particles and a transport pipe, show that simulations using Euler-Euler including KTGF and the Gidaspow drag model over-predicted the particle volume fraction in the pipe compared to the experiments. The reason for this discrepancy is that the experimental set-up is modified to give low particle volume fractions in the transport pipe to enable the use of lasers to investigate the flow.
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Currie, T. D. G. "Application of particle image velocimetry to the investigation of gas dynamic flow in pipes." Thesis, Queen's University Belfast, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.411093.
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Schneider, Helfried, Thomas Frank, Klaus Pachler, and Klaus Bernert. "A Numerical Study of the Gas-Particle Flow in Pipework and Flow Splitting Devices of Coal-Fired Power Plant." Universitätsbibliothek Chemnitz, 2002. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-200200348.
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In power plants using large utility coal-fired boilers for generation of electricity the coal is pulverised in coal mills and then it has to be pneumatically transported and distributed to a larger number of burners (e.g. 30-40) circumferentially arranged in several rows around the burning chamber of the boiler. Besides the large pipework flow splitting devices are necessary for distribution of an equal amount of pulverised fuel (PF) to each of the burners. So called trifurcators (without inner fittings or guiding vanes) and ''riffle'' type bifurcators are commonly used to split the gas-coal particle flow into two or three pipes/channels with an equal amount of PF mass flow rate in each outflow cross section of the flow splitting device. These PF flow splitting devices are subject of a number of problems. First of all an uneven distribution of PF over the burners of a large utility boiler leads to operational and maintenance problems, increased level of unburned carbon and higher rates of NOX emissions. Maldistribution of fuel between burners caused by non uniform concentration of the PF (particle roping) in pipe and channel bends prior to flow splitting devices leads to uncontrolled differences in the fuel to air ratio between burners. This results in localised regions in the furnace which are fuel rich, where insufficient air causes incomplete combustion of the fuel. Other regions in the furnace become fuel lean, forming high local concentrations of NOX due to the high local concentrations of O2. Otherwise PF maldistribution can impact on power plant maintenance in terms of uneven wear on PF pipework, flow splitters as well as the effects on boiler panels (PF deposition, corrosion, slagging).
In order to address these problems in establishing uniform PF distribution over the outlet cross sections of flow splitting devices in the pipework of coal-fired power plants the present paper deals with numerical prediction and analysis of the complex gas and coal particle (PF) flow through trifurcators and ''riffle'' type bifurcators. The numerical investigation is based on a 3-dimensional Eulerian- Lagrangian approach (MISTRAL/PartFlow-3D) developed by Frank et al. The numerical method is capable to predict isothermal, incompressible, steady gas- particle flows in 3-dimensional, geometrically complex flow geometries using boundary fitted, block-structured, numerical grids. Due to the very high numerical effort of the investigated gas-particle flows the numerical approach has been developed with special emphasis on efficient parallel computing on clusters of workstations or other high performance computing architectures. Besides the aerodynamically interaction between the carrier fluid phase and the PF particles the gas-particle flow is mainly influenced by particle-wall interactions with the outer wall boundaries and the inner fittings and guiding vanes of the investigated flow splitting devices. In order to allow accurate quantitative prediction of the motion of the disperse phase the numerical model requires detailed information about the particle-wall collision process. In commonly used physical models of the particle-wall interaction this is the knowledge or experimental prediction of the restitution coefficients (dynamic friction coefficient, coefficient of restitution) for the used combination of particle and wall material, e.g. PF particles on steel.
In the present investigation these parameters of the particle-wall interaction model have been obtained from special experiments in two test facilities. Basic experiments to clarify the details of the particle-wall interaction process were made in a test facility with a spherical disk accelerator. This test facility furthermore provides the opportunity to investigate the bouncing process under normal pressure as well as under vacuum conditions, thus excluding aerodynamically influences on the motion of small particles in the near vicinity of solid wall surfaces (especially under small angles of attack). In this experiments spherical glass beads were used as particle material. In a second test facility we have investigated the real impact of non-spherical pulverised fuel particles on a steel/ceramic target. In this experiments PF particles were accelerated by an injector using inert gas like e.g. CO2 or N2 as the carrier phase in order to avoid dust explosion hazards. The obtained data for the particle-wall collision models were compared to those obtained for glass spheres, where bouncing models are proofed to be valid. Furthermore the second test facility was used to obtain particle erosion rates for PF particles on steel targets as a function of impact angles and velocities.
The results of experimental investigations has been incorporated into the numerical model. Hereafter the numerical approach MISTRAL/PartFlow-3D has been applied to the PF flow through a ''riffle'' type bifurcator. Using ICEM/CFD-Hexa as grid generator a numerical mesh with approximately 4 million grid cells has been designed for approximation of the complex geometry of the flow splitting device with all its interior fittings and guiding vanes. Based on a predicted gas flow field a large number of PF particles are tracked throughout the flow geometry of the flow-splitter. Besides mean quantities of the particle flow field like e.g. local particle concentrations, mean particle velocities, distribution of mean particle diameter, etc. it is now possible to obtain information about particle erosion on riffle plates and guiding vanes of the flow splitting device. Furthermore the influence of different roping patterns in front of the flow splitter on the uniformness of PF mass flow rate splitting after the bifurcator has been investigated numerically.
Results show the efficient operation of the investigated bifurcator in absence of particle roping, this means under conditions of an uniform PF particle concentration distribution in the inflow cross section of the bifurcator. If particle roping occurs and particle concentration differs over the pipe cross section in front of the bifurcator the equal PF particle mass flow rate splitting can be strongly deteriorated in dependence on the location and intensity of the particle rope or particle concentration irregularities. The presented results show the importance of further development of efficient rope splitting devices for applications in coal-fired power plants. Numerical analysis can be used as an efficient tool for their investigation and further optimisation under various operating and flow conditions.
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Gomez, Ramirez David. "Heat Transfer and Flow Measurements in an Atmospheric Lean Pre-Mixed Combustor." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/71812.
Full textAbstract:
Energy conservation, efficiency, and environmental responsibility are priorities for modern energy technologies. The ever increasing demands for lower pollutants and higher performance have driven the development of low-emission gas turbine engines, operating at lean equivalence ratios and at increasingly higher turbine inlet temperatures. This has placed new constraints on gas turbine combustor design, particularly in regards to the cooling technologies available for the combustor liner walls. To optimize combustor thermal management, and in turn optimize overall engine performance, detailed measurements of the flame side heat transfer are required. However, given the challenging environment at which gas turbine combustors operate, there are currently only limited studies that quantify flame side combustor heat transfer; in particular at reacting conditions.
The objective of the present work was to develop methodologies to measure heat transfer within a reacting gas turbine combustor. To accomplish this, an optically accessible research combustor system was designed and constructed at Virginia Tech, capable of operating at 650 K inlet temperature, maximum air mass flow rates of 1.3 kg/s, and flame temperatures over 1800 K. Flow and heat transfer measurements at non-reacting and reacting conditions were carried out for Reynolds numbers (Re) with respect to the combustor diameter ranging from ~11 500 to ~140 000 (depending on the condition). Particle Image Velocimetry (PIV) was used to measure the non-reacting flow field within the burner, leading to the identification of coherent structures in the flow that accounted for over 30% of the flow fluctuation kinetic energy along the swirling jet shear layers. The capability of infrared (IR) thermography to image surface temperatures through a fused silica (quartz) glass was demonstrated at non-reacting conditions. IR thermography was then used to measure the non-reacting steady state heat transfer along the combustor liner. A peak in heat transfer was identified at ~1 nozzle diameter downstream of the combustor dome plate. The peak Nusselt number along the liner was over 18 times higher than that predicted from fully developed turbulent pipe flow correlations, which have traditionally been used to estimate flame side combustor heat transfer.
For the reacting measurements, a novel time-dependent heat transfer methodology was developed that allowed for the investigation of transient heat loads, including those occurring during engine ignition and shutdown. The methodology was validated at non-reacting conditions, by comparing results from an experiment with changing flow temperature, to the results obtained at steady state. The difference between the time-dependent and the steady state measurements were between 3% and 17.3% for different mass flow conditions. The time-dependent methodology was applied to reacting conditions for combustor Reynolds numbers of ~12 000 and ~24 000. At an equivalence ratio of ~0.5 and a combustor Reynolds number of ~12 000, the peak heat load location in reaction was shifted downstream by 0.2 nozzle diameters compared to the non-reacting cases. At higher equivalence ratios, and more visibly at a Reynolds number of ~24 000, the heat transfer distribution along the combustor liner exhibited two peaks, upstream and downstream of the impingement location (X/DN=0.8-1.0 and X/DN=2.5). Reacting PIV was performed at Re=12 000 showing the presence of a strong corner recirculation, which could potentially convect reactants upstream of the impingement point, leading to the double peak structure observed.
The methodologies developed have provided insight into heat transfer within gas turbine combustors. The methods can be used to explore additional conditions and expand the dataset beyond what is presented, to fully characterize reacting combustor heat transfer.Ph. D.
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Lucas, William. "Gas flow and star formation in the centre of the Milky Way : investigations with smoothed particle hydrodynamics." Thesis, University of St Andrews, 2015. http://hdl.handle.net/10023/6601.
Full textAbstract:
The centre of the Milky Way, commonly referred to as the Galactic Centre, is roughly that region within 500 pc of the central black hole, Sagittarius A*. Within the innermost parsec around the supermassive black hole Sagittarius A* are more than a hundred massive young stars whose orbits align to form one or possibly two discs. At about 100 pc is a ring containing more than ten million solar masses of molecular gas which could be the origin of some of the most massive star clusters in the Galaxy. I have performed a number of numerical simulations to help us understand how it is that these structures may have been formed. I firstly describe and test an improvement to the smoothed particle hydrodynamics code I used. This improves conservation of energy and momentum in certain situations such as in strong shocks from supernovae, which were to be included in a later chapter. The discs of massive stars around Sagittarius A* are believed to have been born there within fragmenting gaseous discs. This is problematic, as the formation of two stellar discs would require two gaseous counterparts. A method is described of forming multiple discs around a black hole from a single cloud's infall and subsequent tidal destruction. This is due to its prolate shape providing a naturally large distribution in the direction of the angular momentum vectors within the cloud. The resulting discs may then go on to form stars. Energetically, it would appear that a sequence of supernovae could potentially cause a giant molecular cloud to fall inwards towards the central black hole from an originally large orbit around the Galactic Centre. I simulate the impact on a giant molecular cloud of supernovae originating from a massive stellar cluster located a parsec away. Ultimately, the supernovae are found to have little effect. Finally, I simulate the formation of the dense ring of clouds observed in the Central Molec- ular Zone at a distance of about 100 pc from Sgr A*. Infalling gas is shown to be subject to such extreme tidal forces that a single cloud of gas is extended to form a long stream. The ribbon grows to the point that it self-intersects and forms a ring-like structure. Its complexity depends on the orbit of the original cloud. The position-velocity data is compared with observations, and similarities are noted.
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Roclawski, Harald. "PIV Measurements of Channel Flow with Multiple Rib Arrangements." UKnowledge, 2001. http://uknowledge.uky.edu/gradschool_theses/303.
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A model of a gas turbine blade cooling channel equipped with turbulators and a backward facing step geometry was examined. Up to four turbulators oriented cross-stream and inclined 45° to the flow direction were mounted in the channel. The blockage ratio b/H of the turbulators and the height h/H of the backward facing step was 0:125 and 0:14 respectively. The number of turbulators as well as their size was varied. In a preliminary investigation, hot-wire and pressure measurements were taken for three different Reynolds numbers (5,000, 12,000, 18,000)in the center plane of the test section. Subsequently, particle image velocimetry (PIV) measurements were made on the same geometries. Results of PIV measurements for a Reynolds number range of Reb=600 to 5,000 for the turbulators and Reh=1,500 to 16,200 for the backward facing step are presented, where Reynolds numbers are based on turbulator height b and step height h, respectively. Plots of the velocity field, vorticity, reverse flow probability and RMS velocity are shown. The focus is on the steady flow behavior but also the unsteadiness of the flow is discussed in one section. Also reattachment lengths were obtained and compared among the various turbulator arrangements and the backward facing step geometry. It was found that the flow becomes periodic after three or four ribs. For one turbulator, a very large separation region was observed. The magnitude of the skin friction factor was found to be the highest for two ribs. If the first rib is replaced by a smaller rib, the skin friction factor becomes the lowest for this case. Compared to the backward facing step, the flow reattaches earlier for multiple turbulators. A dependency of reattachment length on Reynolds number was not observed.
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Plewacki, Nicholas. "Modeling High Temperature Deposition in Gas Turbines." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1587714424017527.
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内山, 知実, Tomomi UCHIYAMA, 正章 成瀬, Masaaki NARUSE, 吉泰 峯村, and Kiyoshi MINEMURA. "渦法による固気二相自由乱流の数値解法 (数値モデルと二次元混合層への適用)." 日本機械学会, 2000. http://hdl.handle.net/2237/9214.
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YAGAMI, Hisanori, and Tomomi UCHIYAMA. "Numerical Simulation of Particle-Laden Plane Mixing Layer by Three-Dimensional Vortex Method." The Japan Society of Mechanical Engineers, 2006. http://hdl.handle.net/2237/9219.
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Song, Di. "Study of Electrostatic Charging and Particle Wall Fouling in a Pilot-scale Pressurized Gas-Solid Fluidized Bed up to Turbulent Flow Regime." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36007.
Full textAbstract:
In gas-solid fluidized beds, the generation of electrostatic charges due to continuous contacts between fluidizing particles, and the particles and the fluidization vessel wall, is unavoidable. Industrial operations, such as the production of polyethylene, are susceptible to significant operational challenges caused by electrostatics including reactor wall fouling, a problem known as “sheeting”. The formation of particle sheets can require shutdown periods for clean-up which results in significant economic losses. To gain a better understanding of the underlying mechanisms of electrostatic charging in gas-solid fluidized beds, in an attempt to eliminate or minimize this problem, a pilot-scale pressurized gas-solid fluidization system was designed and built, housing an online electrostatic charge measurement technique consisting of two Faraday cups. The system permits the study of the degree of particle wall fouling at pressures and temperatures up to 2600 kPa and 100°C, respectively, and gas velocities up to 1 m/s (covering a range including turbulent flow regime). The system also allowed, for the first time, the measurement of the fluidizing particles’ mass, net charge and size distribution in various regions of the bed, especially those related to the wall coating under the industrially relevant operating conditions of high pressures and gas velocities. Experimental trials were carried out using polyethylene resin received from commercial reactors to investigate the influence of pressure and gas velocity on the bed hydrodynamics and in turn, the degree of bed electrification.
Mechanisms for particle charging, migration and adherence to the column wall were proposed. The size distribution of the gas bubbles shifted towards smaller bubbles as the operating pressure was raised. Thus, higher pressures lead to greater mixing within the bulk of the bed and resulted in a higher degree of particle wall fouling. Moreover, the extent of wall fouling increased linearly with the increase in gas velocity and as the bed transitioned to turbulent regime, due to the increase in particle-wall contacts. Bipolar charging was observed especially within the wall coating with smaller particles being negatively charged. Overall, particle-wall contacts generated negatively charged particles resulting in a net negative charge in the bed, whereas particle-particle contacts generated positively and negatively charged particles resulting in no net charge when entrainment was negligible. The formation of the wall layer and its extent was influenced by the gravitational and drag forces balancing the image force and Coulomb forces (created by the net charge of the bed and the metallic column wall as the attraction between oppositely charged particles).
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Krishnamurthy, Nagendra. "Investigation of Fouling in Wavy-Fin Exhaust Gas Recirculators." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/32012.
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This dissertation presents a detailed account of the study undertaken on the subject of fouling of Exhaust Gas Recirculator (EGR) coolers. The fouling process in EGR coolers is identified to be due to two primary reasons â deposition of fine soot particles and condensation of hydrocarbons known as dry soot and wet soot fouling, respectively. Several numerical simulations are performed to study the fouling process. Preliminary analysis of the particle forces for representative conditions reveal that drag, thermophoresis and Brownian forces are the significant transport mechanisms and among them, the deposition process is dominated by thermophoresis. Soot deposition in a representative turbulent plain channel shows a direct relationship of the amount of deposition with the near-wall temperature gradient. Subsequently, periodic and developing flow simulations are performed on a wavy channel geometry, a common EGR design for various Reynolds numbers and thermal boundary conditions. Constant heat flux boundary condition is used in the periodic fully-developed calculations, which assist in establishing various deposition trends. The wavy nature of the walls is noted to affect the fouling process, resulting in specific deposition patterns. For the lower Reynolds number flows, significantly higher deposition is observed due to the higher particle residence times. On the other hand, the developing flow calculations facilitate the use of wall temperature distributions that typically exist in EGR coolers. The linear dependence of the amount of deposition on the near-wall temperature gradient or in other words, the heat flux, is ascertained. It is also observed in all the calculations, that for the sub-micron soot particles considered, the deposition process is almost independent of the particle size. In addition, the nature of the flow and heat transfer characteristics and the transition to turbulence in a developing wavy channel are studied in considerable detail. Finally, a study on the condensation of heavy hydrocarbons is undertaken as a post-processing step, which facilitates the prediction of the spatial distribution and time-growth of the combined fouling layer. From the calculations, the maximum thickness of the dry soot layer is observed to be near the entrance, whereas for the wet soot layer, the peak is found to be towards the exit of the EGR cooler. Further, parametric studies are carried out to investigate the effect of various physical properties and inlet conditions on the process of fouling.Master of Science
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Drew, Brady Patterson. "Entrainment Characteristics of Turbulent Round Gas Jets Submerged in Water." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/76852.
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The entrainment process in two-phase buoyant jets differs significantly from their singlephase counterparts, and is not well understood. Entrainment models developed for singlephase flow are often used in two-phase jetting simulations, albeit with limited success. In this work, Particle Image Velocimetry (PIV) and shadowgraph flow visualization experiments have been conducted on submerged round gas jets of varying speeds and nozzle diameters with the goal of improving our understanding of the entrainment process in a two-phase (gas-liquid) jet. The total entrainment estimated using the PIV measurements is higher than the respective values suggested by a common empirical model developed for singlephase buoyant jets. A two-phase theoretical entrainment model used for comparison shows an overestimation of entrainment, but predicts the increase in the rate of entrainment with axial distance from the jet nozzle seen in the PIV results.
This thesis also presents advances in PIV processing methodology that were developed concurrently with the entrainment research. The novel Spectral Phase Correlation (SPC) allows for particle displacement to be determined directly from phase information in the Fourier domain. Some of the potential benefits of the SPC explored here include (1) avoidance of errors introduced by spatial peak-finding routines; (2) use of a modal analysis that can be used to provide information such as correlation quality; and (3) introduction of a means of incorporating information from multiple image windows. At low image noise levels, the method performs as well as an advanced CC-based method. However, difficulties unwrapping the aliased phase information cause the SPC's performance to degrade at high noise levels.Master of Science
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Ghazi, Christopher. "Measurement of Fluid and Particle Transport through Narrow Passages." ScholarWorks @ UVM, 2014. http://scholarworks.uvm.edu/graddis/297.
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There are many instances where fluid and particles traveling through a narrow passage, such as a crack in a window or door, have large but sometimes unseen effects on our daily lives. For instance, in the cold months of the year a pressure gradient can exists between the inside and outside of a building which causes cold, outdoor air to flow inside through any cracks; significantly decreasing heating efficiency. This inflow of atmospheric air can bring with it dangerous contaminant particles to the inside of a building. Pollution can also occur inside a structure from internal sources of contamination, such as smoke generation from a fire. This thesis represents a two-fold examination of these phenomena.
The first part of the thesis showcases a method for local measurement of air leakage flow rate, which can be used to quickly assess leakage rates across a surface, such as a window. The method uses a small local enclosure with constant volume placed about a region on the structure under investigation, which is depressurized and injected with a small concentration of carbon dioxide as a tracer gas. The time variation of the pressure and carbon dioxide concentration inside the enclosure are monitored and used to quantify the leakage flow rate as a function of pressure difference. Because of the small size of the enclosure, advanced data processing techniques are necessary to reduce uncertainty in determination of the rate of change of the carbon dioxide concentration that arises from sensor variability. Results of a laboratory demonstration of the proposed leakage detection and characterization device are reported for the problem of leakage through a circular hole in a plate with prescribed pressure differences. Experimental results from the laboratory tests are found to be in excellent agreement with results of a numerical simulation of leakage flow through a hole, as well as predictions from a number of empirical equations for this problem found in the literature.
The second part of the thesis is a numerical study of particle capture in the entrance region of a crack, which is a phenomenon previously not well understood or accounted for in empirical correlations. The computational domain for laminar flow through a crack consists of the crack channel and both inlet and exit reservoirs that are much larger than the channel width. The simulations examined different mechanisms for particle capture within the channel entrance region, including collision on the inlet reservoir wall just outside the crack channel, collision within the crack channel due to cross-stream inertia imparted by the entrance flow, collision induced by Brownian diffusion both on the inlet reservoir wall outside of the channel and within the channel, and gravitational collision within the channel. A detailed study of the variation of the entrance penetration factor with parameters such as the Stokes, Peclet, and Froude numbers was performed, and comparison of the numerical predictions with different theoretical expressions were made when the latter were available. Validity of the assumption of penetration factor independence was also examined for cases where both entrance region inertia and gravitational settling are significant.
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Filatoff, Nicolas. "Rheologie d'un lit de particules : equations generales et lois de comportement." Paris 6, 1988. http://www.theses.fr/1988PA066678.
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Rupp, Jochen. "Acoustic absorption and the unsteady flow associated with circular apertures in a gas turbine environment." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/12984.
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This work is concerned with the fluid dynamic processes and the associated loss of acoustic energy produced by circular apertures within noise absorbing perforated walls. Although applicable to a wide range of engineering applications particular emphasis in this work is placed on the use of such features within a gas turbine combustion system. The primary aim for noise absorbers in gas turbine combustion systems is the elimination of thermo-acoustic instabilities, which are characterised by rapidly rising pressure amplitudes which are potentially damaging to the combustion system components. By increasing the amount of acoustic energy being absorbed the occurrence of thermo-acoustic instabilities can be avoided. The fundamental acoustic characteristics relating to linear acoustic absorption are presented. It is shown that changes in orifice geometry, in terms of gas turbine combustion system representative length-to-diameter ratios, result in changes in the measured Rayleigh Conductivity. Furthermore in the linear regime the maximum possible acoustic energy absorption for a given cooling mass flow budget of a conventional combustor wall will be identified. An investigation into current Rayleigh Conductivity and aperture impedance (1D) modelling techniques are assessed and the ranges of validity for these modelling techniques will be identified. Moreover possible improvements to the modelling techniques are discussed. Within a gas turbine system absorption can also occur in the non-linear operating regime. Hence the influence of the orifice geometry upon the optimum non-linear acoustic absorption is also investigated. Furthermore the performance of non-linear acoustic absorption modelling techniques is evaluated against the conducted measurements. As the amplitudes within the combustion system increase the acoustic absorption will transition from the linear to the non-linear regime. This is important for the design of absorbers or cooling geometries for gas turbine combustion systems as the propensity for hot gas ingestion increases. Hence the relevant parameters and phenomena are investigated during the transition process from linear to non-linear acoustic absorption. The unsteady velocity field during linear and non-linear acoustic absorption is captured using particle image velocimetry. A novel analysis technique is developed which enables the identification of the unsteady flow field associated with the acoustic absorption. In this way an investigation into the relevant mechanisms within the unsteady flow fields to describe the acoustic absorption behaviour of the investigated orifice plates is conducted. This methodology will also help in the development and optimisation of future damping systems and provide validation for more sophisticated 3D numerical modelling methods. Finally a set of design tools developed during this work will be discussed which enable a comprehensive preliminary design of non-resonant and resonant acoustic absorbers with multiple perforated liners within a gas turbine combustion system. The tool set is applied to assess the impact of the gas turbine combustion system space envelope, complex swirling flow fields and the propensity to hot gas ingestion in the preliminary design stages.