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Flow Field of Turbulent Premixed Combustion in a Cyclone-Jet CombustorYAMAMOTO, Kazuhiro, INOUE, Satoshi, YAMASHITA, Hiroshi, SHIMOKURI, Daisuke, ISHIZUKA, Satoru 2 May 2007 (has links)
No description available.
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Numerical study of helicopter combustor and exhaust emissions using large eddy simulationDumrongsak, Janthanee 02 1900 (has links)
Although Large Eddy Simulation (LES) has demonstrated its potential for
modelling the reaction in simple academic combustors, it is more
computationally expensive than Reynolds Averaged Navier-Stokes (RANS)
which has been used widely for industrial cases. The aim of this research is to
employ LES at minimal grid resolution and computational resource
requirements to capture the main characteristics of the reacting flows in a
helicopter combustor and exhaust plume with the focus on NOx emissions.
Test cases have been carried out to validate the current LES code for non-
reacting jet, non-premixed combustion and unstructured grids. Despite the
moderate grid refinement and simple chemistry models employed, the findings
from these test cases have demonstrated good capabilities of the current LES
to capture the mixing, flame and flow characteristics. In a farther test case, a
key gas-phase chemical reaction selected for the helicopter exhaust plume
modelling has also been tested.
The validated LES code is then employed in the numerical study of the reaction
in the helicopter combustor. The LES predictions in terms of the temperature
and EINOx agree generally well with the combustor design, analytical solutions,
previous LES and test measurements. Subsequently, the potential application
of LES for the calibration of simpler models has been assessed for the generic
and helicopter combustors. The results obtained from LES are compared with
those from a one-dimensional combustor performance and emissions code,
HEPHAESTUS, developed within the Cranfield University Power and
Propulsion Department. The discrepancies between the results are found to be
primarily due to specific simplification and assumptions established in the
HEPHAESTUS model which can be addressed.
Finally, LES has been employed to model the transformation of NO to NO2 in
the helicopter exhaust plume. The findings from this research have
demonstrated that, even without the implementation of highly dense mesh or
advanced reaction model, LES is able to provide results with an acceptable
level of fidelity at relatively low computational costs. These advantages make it
a powerful predictive tool for future design and emissions optimisation
investigations, and calibration of other simpler modelling approaches.
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Scalar dissipation rate based flamelet modelling of turbulent premixed flamesKolla, Hemanth January 2010 (has links)
Lean premixed combustion has potential for reducing emissions from combustion devices without compromising fuel efficiency, but it is prone to instabilities which presents design difficulties. From emissions point of view reliable predictions of species formation rates in the flame zone are required while from the point of view of thermo-acoustics the prediction of spatial variation of heat release rate is crucial; both tasks are challenging but imperative in CFD based design of combustion systems. In this thesis a computational model for turbulent premixed combustion is proposed in the RANS framework and its predictive ability is studied. The model is based on the flamelet concept and employs strained laminar flamelets in reactant-to-product opposed flow configuration. The flamelets are parametrised by scalar dissipation rate of progress variable which is a suitable quantity to describe the flamelet structure since it is governed by convection-diffusion-reaction balance and represents the flame front dynamics. This paramaterisation is new. The mean reaction rate and mean species concentrations are obtained by integrating the corresponding flamelets quantity weighted by the joint pdf of the progress variable and its dissipation rate. The marginal pdf of the progress variable is obtained using β-pdf and the pdf of the conditional dissipation rate is presumed to be log-normal. The conditional mean dissipation rate is obtained from unconditional mean dissipation rate which is a modelling parameter. An algebraic model for the unconditional mean scalar dissipation rate is proposed based on the relevant physics of reactive scalar mixing in turbulent premixed flames. This algebraic model is validated directly using DNS data. An indirect validation is performed by deriving a turbulent flame speed expression using the Kolmogorov-Petrovskii-Piskunov analysis and comparing its predictions with experimental data from a wide range of flame and flow conditions. The mean reaction rate closure of the strained flamelets model is assessed using RANS calculations of statistically planar one-dimensional flames in corrugated flamelets and thin reaction zones regimes. The flame speeds predicted by this closure were close to experimental data in both the regimes. On the other hand, an unstrained flamelets closure predicts flame speed close to the experimental data in the corrugated flamelets regime, but over predicts in the thin reaction zones regime indicating an over prediction of the mean reaction rate. The overall predictive ability of the strained flamelets model is assessed via calculations of laboratory flames of two different configurations: a rod stabilised V-flame and pilot stabilised Bunsen flames. For the V-flame, whose conditions correspond to the corrugated flamelets regime, the strained and unstrained flamelets models yield similar predictions which are in good agreement with experimental measurements. For the Bunsen flames which are in the thin reaction zones regime, the unstrained flamelet model predicts a smaller flame brush while the predictions of the strained flamelets model are in good agreement with the experimental data. The major and minor species concentrations are also reasonably well predicted by the strained flamelets model, although the minor species predictions seem sensitive to the product stream composition of the laminar flamelets. The fluid dynamics induced attenuation of the reaction rate is captured by the strained flamelets model enabling it to give better predictions than the unstrained flamelets model in the thin reaction zones regime. The planar flames and laboratory flames calculations illustrate the importance of appropriately accounting for fluid dynamic effects on flamelet structure and the scalar dissipation rate based strained flamelet model seems promising in this respect. Furthermore, this model seems to have a wide range of applicability with a fixed set of model parameters.
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Numerical study of helicopter combustor and exhaust emissions using large eddy simulationDumrongsak, Janthanee January 2014 (has links)
Although Large Eddy Simulation (LES) has demonstrated its potential for modelling the reaction in simple academic combustors, it is more computationally expensive than Reynolds Averaged Navier-Stokes (RANS) which has been used widely for industrial cases. The aim of this research is to employ LES at minimal grid resolution and computational resource requirements to capture the main characteristics of the reacting flows in a helicopter combustor and exhaust plume with the focus on NOx emissions. Test cases have been carried out to validate the current LES code for non- reacting jet, non-premixed combustion and unstructured grids. Despite the moderate grid refinement and simple chemistry models employed, the findings from these test cases have demonstrated good capabilities of the current LES to capture the mixing, flame and flow characteristics. In a farther test case, a key gas-phase chemical reaction selected for the helicopter exhaust plume modelling has also been tested. The validated LES code is then employed in the numerical study of the reaction in the helicopter combustor. The LES predictions in terms of the temperature and EINOx agree generally well with the combustor design, analytical solutions, previous LES and test measurements. Subsequently, the potential application of LES for the calibration of simpler models has been assessed for the generic and helicopter combustors. The results obtained from LES are compared with those from a one-dimensional combustor performance and emissions code, HEPHAESTUS, developed within the Cranfield University Power and Propulsion Department. The discrepancies between the results are found to be primarily due to specific simplification and assumptions established in the HEPHAESTUS model which can be addressed. Finally, LES has been employed to model the transformation of NO to NO2 in the helicopter exhaust plume. The findings from this research have demonstrated that, even without the implementation of highly dense mesh or advanced reaction model, LES is able to provide results with an acceptable level of fidelity at relatively low computational costs. These advantages make it a powerful predictive tool for future design and emissions optimisation investigations, and calibration of other simpler modelling approaches.
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Method for determination of octane rating by flame quenching experimentsBhasin, Ankush 01 December 2010 (has links)
There are numerous numerical and experimental studies to find correlations of octane rating with fuel properties. This thesis was based on the hypothesis that quenching characteristics at ignition locations impact the flame development. Conversely, determination of quenching characteristics might serve as an effective measure to determine the fuel mixture octane number. This hypothesis was tested with premixed flame experiments using primary reference fuels (iso-octane and n-heptane) and commercial grade gasoline. Premixed flame experiments were conducted on a flat flame burner. Primary reference fuels of different ratios were taken and correlated to their respective thermal quenching condition by introducing co-flowing inert gasses at room temperature with fuel-air mixture. The inert gasses that were used in the experiment are nitrogen and helium and the results are analyzed using a camera and an imaging spectrometer. The experimental results support the hypothesis that flame quenching can be correlated to fuel mixture octane number, and holds potential as an alternative method to determine the octane number.
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熱交換器のある場合の触媒フラットバーナの基礎特性坪内, 修, TSUBOUCHI, Osamu, 中村, 佳朗, NAKAMURA, Yoshiaki, RAMEEZ, Mohamed 05 1900 (has links)
No description available.
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メタン・空気予混合気の着火特性に関する詳細素反応機構を考慮した数値解析松山, 竜佐, MATSUYAMA, Ryusuke, 山下, 博史, YAMASHITA, Hiroshi, 山本, 和弘, YAMAMOTO, Kazuhiro 25 October 2006 (has links)
No description available.
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Burning velocity and OH concentration in premixed combustionYamashita, H., Hayashi, N., Ozeki, M., Yamamoto, K. January 2009 (has links)
No description available.
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Local flame structure and turbulent burning velocity by joint PLIF imagingOhnishi, Masahiro, Isii, Shinji, Yamamoto, Kazuhiro January 2011 (has links)
No description available.
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乱流燃焼場における火炎構造と火炎の安定性に及ぼす旋回流の影響YAMAMOTO, Kazuhiro, SUZUKI, Hiromu, 山本, 和弘, 鈴木, 啓夢 08 1900 (has links)
No description available.
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