Spelling suggestions: "subject:"swift""
51 |
Effect of swirl distortion on gas turbine operabilityMehdi, Ahad 05 1900 (has links)
The aerodynamic integration of an aero-engine intake system with the airframe
can pose some notable challenges. This is particularly so for many military air-
craft and is likely to become a more pressing issue for both new military systems
with highly embedded engines as well as for novel civil aircraft configurations.
During the late 1960s with the advent of turbo-fan engines, industry became in-
creasingly aware of issues which arise due to inlet total pressure distortion. Since
then, inlet-engine compatibility assessments have become a key aspect of any new
development. In addition to total temperature and total pressure distortions, flow
angularity and the associated swirl distortion are also known to be of notable con-
cern. The importance of developing a rigorous methodology to understand the
effects of swirl distortion on turbo-machinery has also become one of the major
concerns of current design programmes.
The goal of this doctoral research was to further the current knowledge on
swirl distortion, and its adverse effects on engine performance, focusing on the
turbo-machinery components (i.e. fans or compressors). This was achieved by
looking into appropriate swirl flow descriptors and by correlating them against the
compressor performance parameters (e.g loss in stability pressure ratios). To that
end, a number of high-fidelity three-dimensional Computational Fluid Dynamics
(CFD) models have been developed using two sets of transonic rotors (i.e. NASA
Rotor 67 and 37), and a stator (NASA Stator 67B). For the numerical purpose,
a boundary condition methodology for the definition of swirl distortion patterns
at the inlet has been developed. Various swirl distortion numerical parametric
studies have been performed using the modelled rotor configurations. Two types of swirl distortion pattern were investigated in the research, i.e. the pure bulk
swirl and the tightly-wound vortex.
Numerical simulations suggested that the vortex core location, polarity, size
and strength greatly affect the compressor performance. The bulk swirl simula-
tions also showed the dependency on swirl strength and polarity. This empha-
sized the importance of quantifying these swirl components in the flow distortion
descriptors. For this, a methodology have been developed for the inlet-engine
compatibility assessment using different types of flow descriptors. A number of
correlations have been proposed for the two types of swirl distortion investigated
in the study.
|
52 |
Měření rychlostních profilů za vířičem / Velocity profile measurement downstream of swirlerZejda, Vojtěch January 2015 (has links)
A burner is very important device in process furnaces that significantly affect the production of emissions during the combustion process. One of the key things in development of the modern low-NOX burners is the evaluation of flow field downstream of an axial blade swirler inside the burner. The computational fluid dynamics (CFD) is often used to predict the attributes of the flow. Predicted values should be validated with measurement. It is the reason why the velocity fields for several choosen swirlers were measured. The hot wire anemometry was choosen and the dual-sensor probe was used during the measurement. The data can be then used for CFD validation. This thesis describes procedure of measurement set-up. The experimental facility was designed according to the anemometry method. The new probe traversing system was designed, which provides desired accuracy. Five different swirlers were measured. Large data set, need for customized post-processing and control over calculation procedures lead to new software design. For each swirler the velocity profiles were gathered and the swirl numbers calculated. That final data were transferred in to graphical format. Uncertainty of measured data was calculated. Results show counter-rotating flow in some areas closed to the swirler. Some drawbacks of current measurement set-up are discussed. Based on the thesis reader can obtain the information and knowledge for consequent measurements of swirl burners velocity profiles.
|
53 |
Numerical Modeling and Analysis of Fluid Flow and Heat Transfer in Circular Tubes Fitted with Different Helical Twisted Core-FinsDongaonkar, Amruta J. 21 October 2013 (has links)
No description available.
|
54 |
Secondary Clarifier Modeling: A Multi-Process ApproachGriborio, Alonso 08 May 2004 (has links)
The performance of settling tanks depends on several interrelated processes and factors that include: hydrodynamics, settling, turbulence, sludge rheology, flocculation, temperature changes and heat exchange, geometry, loading, the nature of the floc, the atmospheric conditions and the total dissolved solids concentration. A Quasi-3D (Q3D) clarifier model has been developed to include the following factors: axisymmetric hydrodynamics (including the swirl component), five types of settling (nonsettleable particles, unflocculated discrete settling, flocculated discrete settling, hindered settling and compression), turbulence, sludge rheology, flocculation with four classes of particles, temperature changes and surface heat exchange with the atmosphere, various external and internal geometry configurations, unsteady solids and hydraulic loading, the nature of the floc settling/interaction. The model includes: shear flocculation, differential settling flocculation and sweep flocculation. The Q3D model reproduces the major features of the hydrodynamic processes and solids distribution on secondary clarifiers. When the model is executed with the field derived settling characteristics, it can accurately predict the effluent and recirculation suspended solids concentrations. The model has been formulated to conserve fluid, tracer and solids mass. The model has been developed and tested using field data from the UNO Pilot Plant and the Jefferson Parish Waste Water Treatment Plant located at Marrero, Louisiana. A field testing procedure is presented that addressees all of the settling regimes that are encountered in a Secondary Settling Tank. Results obtained with the Q3D model indicate that the flocculation process plays a major role in the effluent suspended solids (ESS) on secondary clarifiers. The extent of actual flocculation depends on the design of the center well and on the concentration of the incoming mixed liquor suspended solids (MLSS). The center well promotes flocculation, but its most important benefit is the improvement on the tank hydrodynamics. The changes in temperature on secondary clarifiers play an important role on the performance of secondary settling tanks. The gravity induced radial velocities in the sludge blanket are higher than the radial velocities of the scraper in the region near the hopper, therefore the blades are not highly effective in conveying the solids in this region.
|
55 |
Medição do número de swirl utilizando dutos de admissão do cabeçote de um motor diesel produzidos via prototipagem rápida. / Swirl number measurement using cylinder head intake ports from a diesel engine manufactured via rapid prototype techniques.Martioli, Gustavo Fernandes 06 April 2017 (has links)
O presente trabalho propõe a execução de ensaios de medição do número de swirl em bancada de fluxo em regime permanente, com a utilização de um dispositivo modular e dutos de admissão do cabeçote de um motor diesel produzidos via prototipagem rápida (PR). A medição do número de swirl com dutos produzidos via PR, traz como principais vantagens: reprodutibilidade dos ensaios, facilidade de simular e mensurar o número de swirl dos potenciais desvios no processo de fundição ou usinagem, além da redução no tempo para o desenvolvimento de novas geometrias dos dutos de admissão. O trabalho é experimental e uma unidade do cabeçote estudado foi encaminhado para o laboratório da EPUSP e o número de swirl medido para posterior comparação dos dados. Após a fase inicial de aquisição de dados e ajustes no projeto do dispositivo, essa unidade do cabeçote foi seccionada e digitalizada para que a geometria interna fosse reproduzida via prototipagem rápida. Os dutos de admissão foram montados no dispositivo modular para a realização dos testes em bancada. Todos os testes foram realizados no mesmo equipamento e com o mesmo sistema de controle, com o intuito de reduzir o número de variáveis externas na aquisição de dados. Quando realizou-se a comparação das médias dos resultados do número de swirl do cabeçote e do dispositivo modular com o uso de prototipagem rápida não foram encontradas diferenças estatisticamente significantes. O método proposto representou o escoamento de ar da admissão do modelo de cabeçote analisado. / The present work proposes to execute steady state bench test, swirl number measurements, using a modular device and cylinder head intake ports from a diesel engine manufactured via rapid prototype (RP) techniques. Swirl number measurements with intake ports produced by RP, bring as main advantages: Tests reproducibility, easy to measure the swirl number variances in consequence of potential casting or machining process deviations besides of time reduction to the development of new intake ports geometry. The research is experimental and one sample of the investigated cylinder head was sent to the laboratory and the swirl number was measured for later results comparison. After the early development phase of data acquisition and design improvements, this cylinder head sample was then sectioned and digitalized as to know to have the same internal geometry in the intake ports produced via rapid prototype. The intake ports were assembled in the modular device to perform bench tests. All tests were performed in the same rig and with the same control system with aiming to reduce the external variables during data acquisition. When the mean results analysis was performed in order to compare the results between cylinder head and modular device using rapid prototype, no statistically significant changes were found. The proposed method represented the investigated cylinder head´s intake air flow.
|
56 |
Influência do posicionamento dos dutos de admissão de um cabeçote fundido e usinado no resultado swirl. / Influence of the intake ports positioning of cast and machined cylinder head on the swirl result.Xavier, Ewerton Correa dos Reis 17 August 2017 (has links)
O objetivo deste trabalho é avaliar a influência sobre o número de swirl e desempenho do motor diesel a partir de cabeçotes fabricados com variação no posicionamento relativo dos dutos de admissão em duas direções perpendiculares. Inicialmente definiu-se que o valor a ser deslocado seria de 1 milímetro, e então para cada combinação entre os dutos de admissão curto e longo deveria ser fabricado um número mínimo de seis cabeçotes para posteriores ensaios em bancada com dinamômetro. Após a fundição fabricar as nove combinações definidas, sendo uma delas com os eixos em suas condições nominais, isto é, sem o deslocamento de um milímetro, obtiveram-se um total de 60 cabeçotes. Os cabeçotes foram então controlados em máquina tridimensional, usinados e montados todos os seus componentes e enviados para a medição do número de swirl em máquina desenvolvida especialmente para este teste. Para cada cabeçote mediu-se o número de swirl duas vezes, e em seguida cada uma das nove combinações foram ensaiadas no mesmo dinamômetro e avaliados os respectivos parâmetros: consumo específico de combustível, curva de torque e emissão de poluentes. Para cada combinação mediu-se a curva de torque duas vezes e mediu-se três vezes o ciclo de emissões com treze pontos (ESC). Nos resultados de swirl, três combinações apresentaram-se fora dos limites da tolerância, uma abaixo do mínimo da tolerância em 22,7% e as outras duas além do máximo da tolerância em respectivamente 18,2% e 17,8%. Nos resultados de dinamômetro, nenhuma combinação se apresentou fora dos limites estabelecidos para o modelo de motor ensaiado nos seguintes parâmetros: consumo específico de combustível, torque e emissões de CO, HC, MP e NOx. / The main purpose of this work is to evaluate the influence on the swirl number and the engine diesel performance based on cylinder heads produced with variation on relative positioning of inlet ports in two perpendicular directions. Firstly, it was defined that the value to be displaced would be 1 millimeter, and then for each combination between the short and the long inlet ports should be produced a minimum of six cylinder heads for further testing on the dynamometer. After the foundry production of the defined nine combinations, one of them having the axis in their nominal positions, i.e. without the displacement of 1 millimeter, a total of 60 cylinder heads were obtained. These cylinder heads were measured in a tridimensional machine, machined and all of their components were assembled and their swirl number were measured in the machine developed specially for this method. For each cylinder head the swirl number was measured twice and after that all nine combinations were performed at the same dynamometer and the following parameters were evaluated: fuel consumption, torque curve and pollutants emission. For each combination the torque curve was measured twice and the thirteen point\'s emissions cycle (ESC) was measured three times. Concerning the swirl results, three combinations ended up out of the tolerance limits, one of them as 22,7% below the minimum tolerance and the other two as 18,2% and 17,8% respectively over the maximum tolerance. Regarding the dynamometer results, no combination ended up out of defined tolerances for the kind of engine tested in the following parameters: fuel consumption specific, torque and emissions of CO, HC, PM and NOx.
|
57 |
Influência do posicionamento dos dutos de admissão de um cabeçote fundido e usinado no resultado swirl. / Influence of the intake ports positioning of cast and machined cylinder head on the swirl result.Ewerton Correa dos Reis Xavier 17 August 2017 (has links)
O objetivo deste trabalho é avaliar a influência sobre o número de swirl e desempenho do motor diesel a partir de cabeçotes fabricados com variação no posicionamento relativo dos dutos de admissão em duas direções perpendiculares. Inicialmente definiu-se que o valor a ser deslocado seria de 1 milímetro, e então para cada combinação entre os dutos de admissão curto e longo deveria ser fabricado um número mínimo de seis cabeçotes para posteriores ensaios em bancada com dinamômetro. Após a fundição fabricar as nove combinações definidas, sendo uma delas com os eixos em suas condições nominais, isto é, sem o deslocamento de um milímetro, obtiveram-se um total de 60 cabeçotes. Os cabeçotes foram então controlados em máquina tridimensional, usinados e montados todos os seus componentes e enviados para a medição do número de swirl em máquina desenvolvida especialmente para este teste. Para cada cabeçote mediu-se o número de swirl duas vezes, e em seguida cada uma das nove combinações foram ensaiadas no mesmo dinamômetro e avaliados os respectivos parâmetros: consumo específico de combustível, curva de torque e emissão de poluentes. Para cada combinação mediu-se a curva de torque duas vezes e mediu-se três vezes o ciclo de emissões com treze pontos (ESC). Nos resultados de swirl, três combinações apresentaram-se fora dos limites da tolerância, uma abaixo do mínimo da tolerância em 22,7% e as outras duas além do máximo da tolerância em respectivamente 18,2% e 17,8%. Nos resultados de dinamômetro, nenhuma combinação se apresentou fora dos limites estabelecidos para o modelo de motor ensaiado nos seguintes parâmetros: consumo específico de combustível, torque e emissões de CO, HC, MP e NOx. / The main purpose of this work is to evaluate the influence on the swirl number and the engine diesel performance based on cylinder heads produced with variation on relative positioning of inlet ports in two perpendicular directions. Firstly, it was defined that the value to be displaced would be 1 millimeter, and then for each combination between the short and the long inlet ports should be produced a minimum of six cylinder heads for further testing on the dynamometer. After the foundry production of the defined nine combinations, one of them having the axis in their nominal positions, i.e. without the displacement of 1 millimeter, a total of 60 cylinder heads were obtained. These cylinder heads were measured in a tridimensional machine, machined and all of their components were assembled and their swirl number were measured in the machine developed specially for this method. For each cylinder head the swirl number was measured twice and after that all nine combinations were performed at the same dynamometer and the following parameters were evaluated: fuel consumption, torque curve and pollutants emission. For each combination the torque curve was measured twice and the thirteen point\'s emissions cycle (ESC) was measured three times. Concerning the swirl results, three combinations ended up out of the tolerance limits, one of them as 22,7% below the minimum tolerance and the other two as 18,2% and 17,8% respectively over the maximum tolerance. Regarding the dynamometer results, no combination ended up out of defined tolerances for the kind of engine tested in the following parameters: fuel consumption specific, torque and emissions of CO, HC, PM and NOx.
|
58 |
Etude de la stabilité et des émissions polluantes des flammes turbulentes de prémélange pauvre à haute pression appliquées aux turbines à gazVauchelles, David 20 December 2004 (has links) (PDF)
La combustion en mode pauvre prémélangé permet de réduire les émissions polluantes, mais elle est limitée par l'apparition de fortes instabilités. Afin d'étudier ces instabilités, nous avons conçu une chambre de combustion proche d'une configuration industrielle fonctionnant au gaz naturel. La chambre, pressurisée à 5 bar, est munie de deux dispositifs d'injection d'air: air secondaire et air de dilution. Le prémélange est créé par un injecteur constitué d'un swirl axial et d'un bluff body.<br />L'étude de l'instabilité a été effectuée en fonction de plusieurs paramètres: température d'entrée d'air, débit, richesse de combustion, angle du swirl, présence d'une flamme pilote, position des orifices d'injection d'air secondaire et géométrie du fond de chambre. Pour chaque configuration nous avons mesuré le champ de vitesse, les émissions polluantes, l'émission spontanée du radical CH* et l'évolution temporelle de la pression dans la chambre de combustion. Le résultat principal montre que les injections d'air secondaire jouent un rôle important et complexe dans les chambres de combustion notamment sur la structure et la dynamique de la flamme.<br />Les spectres temporels de pression et de CH* ont montré plusieurs fluctuations temporelles de la combustion que nous avons classées en trois categories: <br />- Les fluctuations basses fréquences dues aux instabilités de combustion<br />- Les fluctuations convectives dont les fréquences ne dépendent que de la vitesse de l'écoulement<br />- Les fluctuations acoustiques dont les fréquences ne dépendent que de la température de l'écoulement<br />L'étude locale des émissions de CH* montre que les positions des maximums de fluctuations se situent à des emplacements différents dans la zone de réaction suivant le régime de combustion. Nous avons adapté localement le modèle du temps de retard (time lag) qui permet de connaître les conditions favorables d'amplification d'une perturbation convective. Les résultats montrent que nous pouvons prédire la position et l'intensité des fluctuations convectives dans la zone réactive en fonction de la température d'entré ou de la puissance de l'installation. Toutefois, ce modèle trouve ses limites lorsque l'interaction de l'air de dilution secondaire devient trop importante avec la zone de réaction.
|
59 |
Determination of flame characteristics in a low swirl burner at gas turbine conditions through reaction zone imagingPeriagaram, Karthik Balasubramanian 27 August 2012 (has links)
This thesis explores the effects of operating parameters on the location and shape of lifted
flames in a Low Swirl Burner (LSB). In addition, it details the development and analysis of
a CH PLIF imaging system for visualizing flames in lean combustion systems. The LSB is
studied at atmospheric pressure using LDV and CH PLIF. CH* chemiluminescence is used
for high pressure flame imaging.
A four-level model of the fluorescing CH system is developed to predict the signal intensity
in hydrocarbon flames. Results from imaging an atmospheric pressure laminar flame are used
to validate the behavior of the signal intensity as predicted by the model. The results show
that the fluorescence signal is greatly reduced at high pressure due to the decreased number
of CH molecules and the increased collisional quenching rate. This restricts the use of this
technique to increasingly narrow equivalence ratio ranges at high pressures. The limitation
is somewhat alleviated by increasing the preheat temperature of the reactant mixture. The
signal levels from high hydrogen-content syngas mixtures doped with methane are found to
be high enough to make CH PLIF a feasible diagnostic to study such flames. Finally, the
model predicts that signal levels are unlikely to be significantly affected by the presence of
strain in the flow field, as long as the flames are not close to extinction.
The results from the LSB flame investigation reveal that combustor provides reasonably
robust flame stabilization at low and moderate values of combustor pressure and reference
velocities. However, at very high velocities and pressures, the balance between the reactant
velocity and the turbulent flame speed shifts in favor of the former resulting in the flame
moving downstream. The extent of this movement is small, but indicates a tendency towards
blow off at higher pressures and velocities that may be encountered in real world gas turbine
applications. There is an increased tendency of relatively fuel-rich flames to behave like
attached flames at high pressure. These results raise interesting questions about turbulent
combustion at high pressure as well as provide usable data to gas turbine combustor designers
by highlighting potential problems.
|
60 |
Some Aspects of Improving Initial Filling Conditions and Steel Cleanliness by Flow Pattern Control Using a Swirling Flow in the Uphill Teeming ProcessTan, Zhe January 2013 (has links)
The flow pattern has widely been recognized to have an impact on the exogenous non-metallic inclusion generation in the gating system and mold flux entrapment in the uphill teeming process. Thus, a well-controlled flow pattern during the teeming process can improve the quality of ingots and further increase the yield during steel production. The current study focused on investigating and optimizing the flow pattern of steel in the gating system and molds to improve steel cleanliness during the initial filling moment. A mathematical model considering a trumpet was initially compared to a reduced model only considering part of the runner channel. Thereafter, the influence of swirl blades implemented at the bottom of the vertical runner on the improvement of initial filling conditions in the molds was investigated in a model considering the entire mold system including a trumpet. The effects of a swirl blade orientation on a swirling flow were further discussed. The simulation results, when utilizing swirl blades, were also verified by plant trials performed at Scana Steel. In addition, a new novel swirling flow generation component, TurboSwirl, was studied in a model considering the entire mold system including a trumpet. The model was based on modifications of the refractory geometry at the elbow of the runners near the mold without the usage of an inserted flow control device in the gating system. Owing to its great potential for improving the flow pattern of steel during the initial filling moment, the effect of TurboSwirl on steel cleanliness was also studied. The results showed that the initial filling conditions during the uphill teeming process can be improved by using a swirl blade or a TurboSwirl in the gating system. This makes it possible to further decrease the initial position of mold powder bags. In addition, it reduces the possibilities of exogenous non-metallic inclusion generation in the gating system as well as mold flux entrapment in the mold during the uphill teeming process. However, the utilization of swirl blades created a considerable amount of droplets when steel entered the molds during the first couple of seconds, which also was verified by the plant trials. The introduction of TurboSwirl showed a greater potential than a swirl blade due to a more evenly distributed swirling flow. The DPM model adopted in the simulations revealed that the TurboSwirl can improve steel cleanliness by increasing the non-metallic inclusion collision rate both with respect to Stokes and turbulent collisions. / <p>QC 20130204</p>
|
Page generated in 0.0527 seconds