• Title/Summary/Keyword: Scalar Mixing

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Analysis for Scalar Mixing Characteristics using Linear Eddy Model (Linear Eddy Model을 이용한 스칼라의 혼합특성 해석)

  • Kim, Hoo-Joong;Kim, Yong-Mo;Ahn, Kook-Young
    • 한국연소학회:학술대회논문집
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    • 2004.06a
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    • pp.133-137
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    • 2004
  • The present study is focused on the small scale turbulent mixing processes in the scalar field. In order to deal with molecular mixing in turbulent flow, the linear eddy model is addressed. In each realization, the molecular mixing term is implemented deterministically, and turbulent stirring is represented by a sequence of instantaneous, statistically independent rearrangement event called by triplet map. The LEM approach is applied with relatively simple conditions. The characteristics of scalar mixing and PDF profiles are addressed in detail.

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Analysis for Scalar Mixing Characteristics using Linear Eddy Model (Linear Eddy Model을 이용한 스칼라의 혼합특성 해석)

  • Kim, H.J.;Ryu, L.S.;Kim, Y.M.
    • Journal of ILASS-Korea
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    • v.11 no.1
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    • pp.1-6
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    • 2006
  • The present study is focused on the small scale turbulent mixing processes in the scalar Held. In order to deal with molecular mixing in turbulent flow, the linear eddy model is addressed. In each realization, the molecular mixing term is implemented deterministically, and turbulent stirring is represented by a sequence of instantaneous, statistically independent rearrangement event called by triplet map. The LEM approach is applied with relatively simple conditions. The characteristics of scalar mixing and PDF profiles are addressed in detail.

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RANS-LES Simulations of Scalar Mixing in Recessed Coaxial Injectors (RANS 및 LES를 이용한 리세스가 있는 동축분사기의 유동혼합에 대한 수치해석)

  • Park, Tae-Seon
    • Journal of the Korean Society of Propulsion Engineers
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    • v.16 no.1
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    • pp.55-63
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    • 2012
  • The turbulent flow characteristics in a coaxial injector were investigated by the nonlinear $k-{\varepsilon}-f_{\mu}$ model of Park et al.[1] and large eddy simulation (LES). In order to analyze the geometric effects on the scalar mixing for nonreacting variable-density flows, several recessed lengths and momentum flux ratios are selected at a constant Reynolds number. The nonlinear $k-{\varepsilon}-f_{\mu}$�� model proposed the meaningful characteristics for various momentum flux ratios and recess lengths. The LES results showed the changes of small-scale structures by the recess. When the inner jet was recessed, the development of turbulent kinetic energy became faster than that of non-recessed case. Also, the mixing characteristics were mainly influenced by the variation of shear rates, but the local mixing was changed by the adoption of recess.

Modeling of Turbulent Molecular Mixing by the PDF Balance Method for Turbulent Reactive Flows (난류연소 유동장에서의 확률밀도함수 전달방정식을 이용한 난류혼합 모델링)

  • Moon, Hee-Jang
    • Journal of the Korean Society of Combustion
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    • v.2 no.1
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    • pp.39-51
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    • 1997
  • A review of probability density function(PDF) methodology and direct numerical simulation for the purpose of modeling turbulent combustion are presented in this study where particular attention is focused on the modeling problem of turbulent molecular mixing term appearing in PDF transport equation. Existing mixing models results were compared to those evaluated by direct numerical simulation in a turbulent premixed medium with finite rate chemistry in which the initial scalar field is composed of pockets of partially burnt gases to simulate autoignition. Two traditional mixing models, the least mean square estimations(LMSE) and Curl#s model are examined to see their prediction capability as well as their modeling approach. Test calculations report that the stochastically based Curl#s approach, though qualitatively demonstrates some unphysical behaviors, predicts scalar evolutions which are found to be in good agreement with statistical data of direct numerical simulation.

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Numerical Analysis on Mixing Efficiency in a Micro-channel with Varied Geometry (미소 채널의 형상변화에 의한 혼합효율에 관한 수치 해석적 연구)

  • Yoon, Joon-Yong;Han, Gyu-suk;Byun, Sung-Joon
    • Applied Chemistry for Engineering
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    • v.16 no.2
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    • pp.275-281
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    • 2005
  • In this work, Scalar Passive code in Lattice Boltzmann Method was employed to simulate mixing performance of Passive mixer in a micro-channel. It physically analyzed stream line and Pressure drop for passive mixer in a micro-channel. The flow characteristics in a micro-channel was a function of Peclet number. The results indicated that the size of static element was more effect on the mixing than the number of static element and the distance of static elements.

Flame Hole Dynamics Model of a Diffusion Flame in Turbulent Mixing Layer (난류 혼합층에서 확산화염에 대한 flame hole dynamics 모델)

  • Kim, Jun-Hong;Chung, S.H.;Ahn, K.Y.;Kim, J.S.
    • Journal of the Korean Society of Combustion
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    • v.8 no.3
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    • pp.15-23
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    • 2003
  • Partial quenching structure of turbulent diffusion flames in a turbulent mixing layer is investigated by the method of flame hole dynamics in order to develop a prediction model for turbulent flame lift off. The essence of flame hole dynamics is derivation of the random walk mapping, from the flame-edge theory, which governs expansion or contraction of flame holes initially created by local quenching events. The numerical simulation for flame hole dynamics is carried out in two stages. First, a direct numerical simulation is performed for constant-density fuel-air channel mixing layer to obtain the turbulent flow and mixing fields, from which a time series of two dimensional scalar dissipation rate array is extracted at a fixed virtual flame surface horizontally extending from the end of split plate to the downstream. Then, the Lagrangian simulation of the flame hole random walk mapping projected to the scalar dissipation rate array yields temporally evolving turbulent extinction process and its statistics on partial quenching characteristics. The statistical results exhibit that the chance of partial quenching is strongly influenced by the crossover scalar dissipation rate while almost unaffected by the iteration number of the mapping that can be regarded as a flame-edge speed.

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Confined laminar vortex shedding and scalar mixing around a square cylinder with a jet (Jet가 분출되는 채널내 정사각단면 실린더 주위유동 및 혼합현상)

  • Eom, Jun-Seok;Kim, Don-Hyeong;Yang, Kyung-Soo
    • Proceedings of the KSME Conference
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    • 2000.04b
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    • pp.759-764
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    • 2000
  • In this study, the confined laminar flow around a square cylinder, which ejects a either on the front face or on the rear face, is numerically simulated. In each case, three ratios of jet velocity to the fixed upstream velocity are considered. In all cases of the rear fuel jet, the high mass-fraction region is formed along the streamlines from the jet exit. In case of front jet, drag is significantly decreased when the jet velocity ratio is greater than 1. The results obtained exhibit flow and scalar-mixing characteristics encountered in a planar combustor

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Measurement of Flow and Scalar Distribution at Gas Turbine Inlet Section (가스터빈 입구에서의 유동 및 스칼라 분포 특성)

  • Hong, Sung-Kook;Ireland, Peter;Denman, Paul
    • The KSFM Journal of Fluid Machinery
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    • v.13 no.4
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    • pp.45-50
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    • 2010
  • The goal of paper is to investigate the flow and scalar distribution through the HP Nozzle Guide Vane (NGV) passage. Flow and scalar distribution measurement are conducted by using 5-hole pressure probe and $CO_2$ tracing technique, respectively. Three different experimental cases are considered depending on cooling flow condition. The result shows that the vortical secondary flow patterns are observed clearly and these flow characteristics maintain through the NGV passage regardless of cooling flow injection. Compared to center region, the high axial velocity flow is observed near wall region due to cooling flow injection. Without cooling flow, the $CO_2$ (scalar) distribution becomes to be uniform quickly due to the strong flow mixing phenomenon. However, in cases of cooling flow, scalar distribution is significantly non-uniform.

NUMERICAL ANALYSIS ON THE MIXING OF A PASSIVE SCALAR IN THE TURBULENT FLOW OF A SMALL COMBUSTOR BY USING LARGE EDDY SIMULATION (큰에디모사법을 이용한 소형 연소기의 난류 유동장 내 스칼라 혼합에 대한 수치해석)

  • Choi, H.S.;Park, T.S.;Suzuki, K.
    • Journal of computational fluids engineering
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    • v.11 no.4 s.35
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    • pp.67-74
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    • 2006
  • The characteristics of turbulent flow and mixing in a small can type combustor are investigated by means of Large Eddy Simulation (LES). Attention is paid for a combustor having a baffle plate with oxidant injection and fuel injection holes and study is made for three cases of different baffle plate configurations. From the result, it is confirmed that mixing is promoted by interaction between the jets during their developing process and large vortical flows generated in the vicinity of the combustor wall or fuel jet front. This particular flow feature is effective to accelerate the slow mixing between fuel and oxidant suffering from low Reynolds number condition in such a small combustor. In particular, the vortical flow region ahead of fuel jet plays an important role for rapid mixing. Discussion is made for the time and space averaged turbulent flow and scalar quantities which show peculiar characteristics corresponding to different vortical flow structures for each baffle plate shapes.

Large-Eddy Simulation of Turbulent Flows in a Planar Combustor (Planar-Jet형 연소기 내 난류유동의 LES)

  • Kim, Do-Hyeong;Yang, Kyung-Soo;Shin, Dong-Shin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.10
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    • pp.1409-1416
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    • 2000
  • In this study, turbulent flows in a planar combustor which has a square rib-type flame holder are numerically investigated by Large Eddy Simulation(LES). Firstly, the flow fields with or without jet injection downstream of the flame-holder are examined using uniform inlet velocity. Comparison of the present LES results with experimental one shows a good agreement. Secondly, to investigate mixing of oxidizer(air) and fuel injected behind the flame holder, the scalar-transport equation is introduced and solved. From the instantaneous flow and scalar fields, complex and intense mixing phenomena between fuel and jet are observed. It is shown that the ratio of jet to blocked air velocity is an important factor to determine the flow structure. Especially, when the ratio is large enough, the fuel jet penetrates the main vortices shed from the flame holder, resulting in significant changes in the flow and scalar fields.