1,588 research outputs found

    Radially Symmetrical Flow of Reacting Liquid With Changing Viscosity

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    Frontal regimens for one-dimensional flow of reacting liquid with changing viscosity are studied. Stationary solutions are investigated for the case of narrow reaction zones that shrink to a front. The results of numerical solution of the nonstationary problem are presented. Complex oscillations resulting from period-doubling bifurcations are found

    Comparison of numerical and experimental results of four liquid spray combustors

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    Validation of CFD predictions for liquid spray combustion application is a challenging task due to difficulties in both modeling and experimental measurements. Validation is considered to be a key step for successful CFD predictions of combustion systems. The goals of this thesis are threefold: (1) validation of models used for spray combustion predictions, (2) using the validated predictions to explain steady flow and combustion physics, and (3) using the validated procedure to simulate conditions where unstable combustion behavior is observed experimentally, and to explore if such unstable behavior can be predicted correctly. The model validation is done with respect to three experimental data sets for spray combustors, and it is shown that predictions match data reasonably well. The validated code is then used to predict and understand the flow and combustion behavior for both steady and unsteady combustion conditions

    Spray combustion experiments and numerical predictions

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    The next generation of commercial aircraft will include turbofan engines with performance significantly better than those in the current fleet. Control of particulate and gaseous emissions will also be an integral part of the engine design criteria. These performance and emission requirements present a technical challenge for the combustor: control of the fuel and air mixing and control of the local stoichiometry will have to be maintained much more rigorously than with combustors in current production. A better understanding of the flow physics of liquid fuel spray combustion is necessary. This paper describes recent experiments on spray combustion where detailed measurements of the spray characteristics were made, including local drop-size distributions and velocities. Also, an advanced combustor CFD code has been under development and predictions from this code are compared with experimental results. Studies such as these will provide information to the advanced combustor designer on fuel spray quality and mixing effectiveness. Validation of new fast, robust, and efficient CFD codes will also enable the combustor designer to use them as additional design tools for optimization of combustor concepts for the next generation of aircraft engines

    Development of Methods to Predict the Effects of Test Media in Ground-Based Propulsion Testing

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    This report discusses work that began in mid-2004 sponsored by the Office of the Secretary of Defense (OSD) Test & Evaluation/Science & Technology (T&E/S&T) Program. The work was undertaken to improve the state of the art of CFD capabilities for predicting the effects of the test media on the flameholding characteristics in scramjet engines. The program had several components including the development of advanced algorithms and models for simulating engine flowpaths as well as a fundamental experimental and diagnostic development effort to support the formulation and validation of the mathematical models. This report provides details of the completed work, involving the development of phenomenological models for Reynolds averaged Navier-Stokes codes, large-eddy simulation techniques and reduced-kinetics models. Experiments that provided data for the modeling efforts are also described, along with with the associated nonintrusive diagnostics used to collect the data

    The numerical prediction of the acoustic response of liquid-fuelled, swirl-stabilised flames

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    This thesis sets out and tests several different approaches to predicting and understanding the acoustic response of an industrially representative liquid fuelled, swirl-stabilised, lean-burn fuel injector using numerical simulations. This work is important as it contributes to the design of fuel injectors with a low susceptibility for thermoacoustic instabilities or ‘rumble’.The flame transfer function (FTF), a transfer function relating the mass flow rate through the fuel injector and heat release rate of the combustor, has been chosen as the best way to describe the flame response as it can be used in conjunction with a acoustic field solver to predict the stability of a combustion system. The FTF of a chosen injector geometry has been predicted using conventional compressible methods and a novel incompressible method which has been shown to be consistent with the compressible method at two frequencies of forcing. This is in contrast with mass flow forced incompressible simulations that fail to reproduce the correct downstream flow field fluctuations. The single phase flow field and acoustic response of the injector has also been predicted and compared to experiments with good agreement.The injector hydrodynamic response has also been investigated along with how hydrodynamics, acoustics, the fuel spray and heat release are related. Acoustic forcing can be seen to actively alter the strength of large scale fluid structures, the mean pressure field and the mass flow rates through the different injector passages. The fuel spray may also couple with these structures causing additional local changes to the mixture fraction field and heat release rates. The effects of fuel spray SMD (Sauter Mean Diamter) and fuel spray injection velocity have on the flame have also been tested showing that the fuel spray atomisation, which can also be affected by acoustic forcing, may play a significant role in combustion instabilities.Several novel numerical methods have been developed and are also discussed in detail includ- ing methods relating to the reproduction of acoustic forcing in incompressible simulations and the reproduction of turbulent fields at inlets. Several innovative post-processing techniques have been employed to identify the relationship between large scale flow structures, the fuel spray and combustion.Modifications of the original injector geometry have been proposed to reduce the sensitivity of the injector to instabilities. These include better atomisation and mixing, better placement of swirl vanes, better aerodynamic design and improved hydrodynamic stability.</div

    Characterization of Horizontally-Issuing Reacting Buoyant Jets

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    This research studied the mixing and combustion behavior of low Reynolds number, horizontally-issuing gaseous fuel jets with ambient air. The study focused on the mixing characteristics of propane and ethylene. These fuels are, respectively, heavy and neutral with respect to air, and were tested at various Froude numbers and laminar tube Reynolds numbers. Using low Froude and Reynolds number flows allowed for isolation of the buoyant jet effects. The process was characterized through the use of a non-invasive, OH Planar Laser-Induced Fluorescence (PLIF) technique, and supplemented with filtered (CH*) and unfiltered high speed imaging. The resulting cross sectional PLIF images were used to produce a three-dimensional mapping of the jet spreading, jet path, and combustion progress through OH concentrations up to x/D = 9, for both fuels. Combustion locations were further visualized and confirmed through CH* high speed imaging

    CFD modelling of gas turbine combustion processes

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    Stationary gas turbines manufacturers and operators are under constant scrutiny to both reduce environmentally harmful emissions and obtain efficient combustion. Numerical simulations have become an integral part of the development and optimisation of gas turbine combustors. In this thesis work, the gas turbine combustion process is analysed in two parts, a study on air-fuel mixing and turbulent combustion. For computational fluid dynamic analysis work the open-source CFD code OpenFOAM and STAR-CCM+ are used. A fuel jet injected to cross-flowing air flow is simplified air-fuel mixing arrangement, and this problem is analysed numerically in the first part of the thesis using both Reynolds Averaged Navier Stokes (RANS) method and Large Eddy Simulation (LES) methods. Several turbulence models are compared against experimental data in this work, and the complex turbulent vortex structures their effect on mixing field prediction is observed. Furthermore, the numerical methods are extended to study twin jets in cross-flow interaction which is relevant in predicting air-fuel mixing with arrays of fuel injection nozzles. LES methods showed good results by resolving the complex turbulent structures, and the interaction of two jets is also visualised. In this work, all three turbulent combustion regimes non-premixed, premixed, partially premixed are modelled using different combustion models. Hydrogen blended fuels have drawn particular interest recently due to enhanced flame stabilisation, reduced CO2 emissions, and is an alternative method to store energy from renewable energy sources. Therefore, the well known Sydney swirl flame which uses CH4: H2 blended fuel mixture is modelled using the steady laminar flamelet model. This flame has been found challenging to model numerically by previous researchers, and in this work, this problem has been addressed with improved combustion modelling approach with tabulated chemistry. Recognizing that the current and future gas turbine combustors operate on a mixed combustion regime during its full operational cycle, combustion simulations of premixed/partially premixed flames are also performed in this thesis work. Dynamical artificially thickened flame model is implemented in OpenFOAM and validated using propagating and stationary premixed flames. Flamelet Generated Manifold (FGM) methods are used in the modelling of turbulent stratified flames which is a relatively new field of under investigation, and both experimental and numerical analysis is required to understand the physics. The recent experiments of the Cambridge stratified burner are studied using the FGM method in this thesis work, and good agreement is obtained for mixing field and temperature field predictions
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