• Title/Summary/Keyword: Turbulent structure

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PSR-Based Microstructural Modeling for Turbulent Combustion Processes and Pollutant Formation in Double Swirler Combustors

  • Kim, Yong-Mo;Kim, Seong-Ku;Kang, Sung-Mo;Sohn, Jeong-Lak
    • Journal of Mechanical Science and Technology
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    • v.15 no.1
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    • pp.88-97
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    • 2001
  • The present study numerically investigates the fuel-air mixing characteristics, flame structure, and pollutant emission inside a double-swirler combustor. A PSR(Perfectly Stirred Reactor) based microstructural model is employed to account for the effects of finite rate chemistry on the flame structure and NO formation. The turbulent combustion model is extended to nonadiabatic flame condition with radiation by introducing an enthalpy variable, and the radiative heat loss is calculated by a local, geometry-independent model. The effects of turbulent fluctuation are taken into account by the joint assumed PDFs. Numerical model is based on the non-orthogonal body-fitted coordinate system and the pressure/velocity coupling is handled by PISO algorithm in context with the finite volume formulation. The present PSR-based turbulent combustion model has been applied to analyze the highly intense turbulent nonpremixed flame field in the double swirler combustor. The detailed discussions were made for the flow structure, combustion effects on flow structure, flame structure, and emission characteristics in the highly intense turbulent swirling flame of the double swirler burner.

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Organized structure of turbulent boundary layer with rod-roughened wall (표면조도가 난류구조에 미치는 영향)

  • Lee, Jae-Hwa;Lee, Seung-Hyun;Kim, Kyoung-Youn;Sung, Hyung-Jin
    • 한국전산유체공학회:학술대회논문집
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    • 2008.03b
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    • pp.189-192
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    • 2008
  • Turbulent coherent structure near rod-roughened wall are investigated by analyzing the database of direct numerical simulation of turbulent boundary layer. The roughness sublayer id defined as two-point correlations are not independent of streamwise locations around roughness. The roughness sublayer based on the two-point spatial correlation is different from that given by one-point statistics. Quadrant analysis and probability-weighted Reynolds shear stress indicate that turbulent structures are not affected by surface roughness above the roughness sublayer defined by the spatial correlations. The conditionally-averaged flow fields associated with Reynolds shear stress producing Q2/Q4 events show that though turbulent vortices are affected in the roughness sublayer, these are very similar at different streamwise locations above the roughness sublayer. The Reynolds stress producing turbulent vortices in the log layer have almost the same geometrical shape as those in the smooth wall-bounded turbulent flows. This suggests that the mechanism by which the Reynolds stress is produced in the log layer has not been significantly affected by the present surface roughness.

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Numerical Analysis on the Turbulent Mixing Flow Field of $45^{\circ}$ Impinging Round Jet ($45^{\circ}$ 원형충돌분류의 난류혼합유동장에 대한 수치해석)

  • Kim, J.K.;Oh, S.H.
    • Journal of Power System Engineering
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    • v.15 no.3
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    • pp.38-45
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    • 2011
  • The computational flow numerical analysis was introduced to predict thc turbulent characteristics in the mixing flow structure of $45^{\circ}$ impinging round jet. This analysis has been carried out through the commercial fluent software. Realizable(RLZ) k-${\varepsilon}$ was used as a turbulent model. It can be known that mean velocities analysed through RLZ k-${\varepsilon}$ turbulent model comparatively predict well the experiments and show well the elliptic shape of mixing flow structure in the Y-Z plane, but analysed turbulent kinetic energies show somewhat differently from the experiments in certain regions.

Numerical Study on Structure and Pollutant Formation for Syngas Turbulent Nonpremixed Swirling Flames (석탄가스 선회난류 비예혼합 화염장의 화염구조 및 NOx 배출특성 해석)

  • Lee, Jeong-Won;Kang, Sung-Mo;Kim, Yong-Mo;Joo, Yong-Jin
    • Journal of the Korean Society of Combustion
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    • v.14 no.2
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    • pp.10-17
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    • 2009
  • The present study numerically investigate the effects of the Syngas chemical kinetics on the basic flame properties and the structure of the Syngas nonpremixed flames. In order to realistically represent the turbulencechemistry interaction and the spatial inhomogeneity of scalar dissipation rate, the Eulerian Particle Flamelet Model (EPFM) with multiple flamelets has been applied to simulate the combustion processes and NOx formation in the syngas turbulent nonpremixed flames. Validation cases include the Syngas turbulent nonpremixed jet and swirling flames. Based on numerical results, the detailed discussion has been made for the effects of the chemical kinetics, the flame structure, and NOx formation characteristics in the turbulent Syngas nonpremixed flames.

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Particle Image Velocimetry Measurement of Unsteady Turbulent Flow around Regularly Arranged High-Rise Building Models

  • Sato, T.;Hagishima, A.;Ikegaya, N.;Tanimoto, J.
    • International Journal of High-Rise Buildings
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    • v.2 no.2
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    • pp.105-113
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    • 2013
  • Recent studies proved turbulent flow properties in high-rise building models differ from those in low-rise building models by comparing turbulent statistics. Although it is important to understand the flow characteristics within and above high-rise building models in the study of urban environment, it is still unknown and under investigation. For this reason, we performed wind tunnel experiment using Particle Image Velocimetry (PIV) to investigate and identify the turbulent flow properties and characteristic flow patterns in high-rise building models. In particular, we focus on instantaneous flow field near the canopy and extracted flow field when homogeneous flow field were observed. As a result, six characteristic flow patterns were identified and the relationship between these flow patterns and turbulent organized structure were shown.

Basis Mode of Turbulent Flame in a Swirl-Stabilized Gas Turbine using LES and POD

  • Sung, Hong-Gye;Yang, Vigor
    • Journal of the Korean Society of Combustion
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    • v.6 no.2
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    • pp.29-35
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    • 2001
  • Unsteady numerical study has been conducted on combustion dynamics of a lean-premixed swirl-stabilized gas turbine swirl injector. A three-dimensional computation method utilizing the message passing interface (MPI) parallel architecture, large eddy simulation(LES), and proper orthogonal decomposition (POD) technique was applied. The unsteady turbulent flame dynamics are simulated so that the turbulent flame structure can be characterized in detail. It was observed that some fuel lumps escape from the primary combustion zone, and move downstream and consequently produce hot spots. Those flame dynamics coincides with experimental data. In addition, basis modes of the unsteady turbulent flame are characterized using proper orthogonal decomposition (POD) analysis. The flame structure based on odd basis modes is apparently larger than that of even ones. The flame structure can be extracted from the summation of the basis modes and eigenvectors at any moment.

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Evaluation of Turbulent Models on the Mixing Flow Structure of $45^{\circ}$ Impinging Jet by Two Round Jets (두 원형분류에 의한 $45^{\circ}$ 충돌분류의 흔합유동구조에 대한 난류모델 평가)

  • Kim, J.K.;Oh, S.H.
    • Journal of Power System Engineering
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    • v.13 no.5
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    • pp.34-39
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    • 2009
  • In this paper, the CFD analysis using various turbulent models has been performed to evaluate which type of turbulent models can predict well the mixing flow structure of $45^{\circ}$ impinging round jet. This CFD analysis has been carried out through the commercial Fluent software. As a result, any of turbulent models cannot predict the experimental results definitely all over the flow range. However, as compared with the experimental results, the turbulent model of realizable(RLZ) k-$\varepsilon$ only predicts well in the limited range between X/$X_0=1.1$ and X/$X_0=2.0$.

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Numerical Study on Flame Structure and Pollutant Formation for Syngas Turbulent Nonpremixed Swirling Flames (석탄가스 난류 선회 비예혼합 연소기의 화염구조 및 공해물질 생성의 해석)

  • Lee, Jeongwon;Kim, Yongmo
    • 한국연소학회:학술대회논문집
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    • 2012.04a
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    • pp.289-291
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    • 2012
  • The present study numerically investigate detailed flame structure of the Syngas diffusion flames. In order to realistically represent the turbulence-chemistry interaction and the spatial inhomogeneity of scalar dissipation rate, the Eulerian Particle Flamelet Model(EPFM) with multiple flamelets has been applied to simulate the combustion processes and NOx formation in the syngas turbulent nonpremixed flames. And level-set approach is also utilized to account for the partially premixing effect at fuel and oxidizer injector in KEPRI nonpremixed combustor. Based on numerical results, the detailed discussion has been made for the precise structure and NOx formation characteristics of the turbulent syngas nonpremixed flames.

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Numerical Analysis for the Detailed Structure of Syngas Turbulent Nonpremixed Flames (석탄가스 난류비예혼합 화염장의 해석)

  • Lee, Jeong-Won;Kim, Chang-Hwan;Kim, Yong-Mo
    • 한국신재생에너지학회:학술대회논문집
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    • 2007.06a
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    • pp.775-778
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    • 2007
  • The present study numerically investigate the detailed structure of the syngas diffusion flames. In order to realistically represent the turbulence-chemistry interaction, the transient flamelet model has been applied to simulate the combustion processes and $NO_X$ formation in the syngas turbulent nonpremixed flames. The single mixture fraction formulation is extended to account for the effects of the secondary inlet mixture. Computations are the wide range of syngas compositions and oxidizer dilutions. Based on numerical results, the detailed discussion has been made for the effects of syngas composition and oxidizer dilution on the structure of the syngas-air and syngas-oxygen turbulent nonpremixed flames.

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An Experimental Study on Turbulent Diffusion Flame in Double Coaxial Air Jets(II) (동축이중 공기분류중의 난류확산화염에 관한 실험적 연구 II)

  • 조용대;최병윤
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.5
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    • pp.1234-1243
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    • 1990
  • Double coaxial are jets(annular and coaxial air jets) between which propane gas is fed was selected to study the structure of diffusion flames in turbulent shear flow. Schlieren and direct photographs are taken to visualize the flame structure. Mean and fluctuating temperatures and ion currents were measured to investigate the macroscopic and the instantaneous flame structure. The objective of this study is to understand the interaction between combustion and mixing process especially in the transition region of turbulent shear flow. The investigation reported in this paper focuses on the macroscopic and the instantaneous structures of three flames obtained. The increased mixing effect resulting from increase of Reynolds number of central air jet makes the flame bluish and short. When the velocity of surrounding air stream is higher than that of central air jet, the instantaneous flame structure is composed of coherent structure. It is considered that the flame structure of transitional region of mixing layer depends on the structure of mixing layer of non-reacting conditions.