• 제목/요약/키워드: Turbulent Dissipation

검색결과 183건 처리시간 0.017초

이상난류제트 유동에서 고체입자 난류확산의 수치모델에 관한 연구 (Study on the numerical models of turbulent dispersion of solid particles in a two-phase turbulent jet flow)

  • 양선규;최영돈
    • 대한기계학회논문집
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    • 제11권1호
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    • pp.1-18
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    • 1987
  • 본 연구에서는 입자가 부상된 이상난류제트유동에 Einstein의 확산모형, Pes- kin모형, 3-방정식 모형, 4-방정식 모형, 대수응력모형 등을 적용하여 해석하고 각 모 형들의 결과를 비교 분석하였다. 이상난류유동의 수치해석에서 공기는 제1유체유동 으로 하고 첨가되는 고체분말의 흐름은 밀도(.rho.$_{p}$), 층류동점성계수(.nu.$_{p}$), 과점성계수(.nu.$_{pt}$ )를 갖는 제2유체유동의 흐름으로 간주하였다.

Experimental Investigation of Scalar Dissipation Rates in Lean Hydrocarbon/Air Premixed Flames

  • Chen, Yung-Cheng;Bilger, Robert W.
    • 한국연소학회지
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    • 제6권2호
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    • pp.43-49
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    • 2001
  • Instantaneous, three-dimensional scalar dissipation rates of the reaction progress variable are measured in turbulent premixed Bunsen flames of lean hydrocarbon/air mixtures with the two-sheet, two-dimensional Rayleigh scattering technique. The flames investigated are located in the turbulent flame-front regime on a newly proposed combustion diagram for premixed flames. The conditionally-averaged mean scalar dissipation rates, $N_{\zeta}$ are found to be lower than the calculated laminar values, indicating a locally broadened flame front. In agreement with previous measurements, the maximum of $N_{\zeta}$, decreases strongly with increasing Karlovitz numbers. The conditional probability density functions are close to a log-normal distribution for scalar dissipation rates conditioned at the progress variable value where the scalar dissipation is maximum in unstretched laminar flame calculations. The time scale for the Favre-averaged mean scalar dissipation rate decreases in general across the turbulent flame brush from the unburnt to burnt side.

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선반주축계의 동특성 향상에 관한 연구 -주축대와 베드의 보울트 결합을 중심으로- (A Study on the Improvement of Dynamic Characteristics of Spindle-Work System in Lathe - Focused on the Bolt Juint between Headstock and Bed -)

  • 신용호;박태원;홍동표;정인성
    • 대한기계학회논문집
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    • 제12권1호
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    • pp.1-7
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    • 1988
  • 본 연구에서는 컬럼모델을 보울트로 고정할 때 접합면에 알루미늄판, 황동판, 스테인리스판 등을 삽입하고 정적강성과 동적특성을 검토하여 이것을 기초로 공작물- 주축대-공구로 형성되고 있는 사이클중에서 선반의 주축대와 베드를 연결하는 결합부에 모델실험을 사용한 게재물을 삽입하고 선반구축계의 동적특성을 검토하였다.

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

  • 김준홍;정석호;안국영;김종수
    • 한국연소학회지
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    • 제8권3호
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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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이차적인 변형률효과를 고려한 텐서 불변성 난류에너지 소산율방정식 (A Tensor Invariant Dissipation Equation Accounting for Extra Straining Effects)

  • 명현국
    • 대한기계학회논문집
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    • 제18권4호
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    • pp.967-976
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    • 1994
  • A tensor invariant model equation for the turbulent energy dissipation rate is proposed in the present study, which is able to simulate secondary straining effects such as curvature effects without the introduction of additional empirical input. The source term in this model has a combined form of the generation term due to the mean vorticity with the conventional one due to the mean strain rate. An extended low-Reynolds-number $k-\epsilon$ turbulence model involving this new model equation is tested for a turbulent Coutte flow between coaxial cylinders with inner cylinder rotated, which is a well defined example of curved flows. The predicted results indicate that the present model works much better for this flow, compared with previous models.

상류유동전개부, 수축부 및 자유분사류로 이어지는 유동장에서의 난류에너지 천이에 대한 연구 (Transition of Turbulent Kinetic Energy Through a Serial Unit of Straight-Duct, Contraction and Free-Jet)

  • 한용운;남경덕
    • 대한기계학회논문집
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    • 제16권12호
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    • pp.2368-2375
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    • 1992
  • 본 연구에서는 축대칭 유동장치를 구성하여 열선 풍속계를 이용, 중심축에 따 른 난류쇠퇴양식을 살펴보고 동시에 난류에너지천이에 대한 세밀한 분석을 통하여 각 각 상류유동전개부, 수축부 및 자유분사류로 연속되는 3개의 유동 구조속에서 어떻게 천이해 갈 것인가를 측정하여 축대칭 유동의 난류구조 변천에 대한 기초 실험자료로 제시하고저 한다.

Level-Set 방법이 적용된 Flame Hole Dynamics 모델을 통한 난류 혼합층 확산화염의 모사 (Simulation of a Diffusion Flame in Turbulent Mixing Layer by the Flame Hole Dynamics Model with Level-Set Method)

  • 김준홍;정석호;안국영;김종수
    • 한국연소학회지
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    • 제9권2호
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    • pp.18-29
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    • 2004
  • Partial quenching structure of diffusion flames in a turbulent mixing layer has been investigated by the method of flame hole dynamics in oder to develope a prediction model for the phenomenon of turbulent flame lift off. The present study is specifically aimed to remedy the shortcoming of the stiff transition of the conditioned partial burning probability across the crossover condition by employing the level-set method which enables us to include the effect of finite flame edge propagation speed. In light of the level-set simulation results with two models for the edge propagation speed, the stabilizing conditions for turbulent lifted flame are suggested. The flame hole dynamics combined with the level-set method yields a temporally evolving turbulent extinction process and its partial quenching characteristics is compared with the results of the previous model employing the flame-hole random walk mapping based on three critical scalar dissipation rates. The probability to encounter reacting state, conditioned with scalar dissipation rate, demonstrated that the conditional probability has a rather gradual transition across the crossover scalar dissipation rate. Such a smooth transition is attributed to the finite response of the flame edge propagation.

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다양한 $k-{\varepsilon}$ 난류모델과 Skew-Upwind 기법에 의한 단이 진 벽면분류에 대한 수치해석 (Numerical Analyses on Wall-Attaching Offset Jet with Various Turbulent $k-{\varepsilon}$ Models and Skew-Upwind Scheme)

  • 서호택;부정숙
    • 대한기계학회논문집B
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    • 제24권2호
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    • pp.224-232
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    • 2000
  • Four turbulent $k-{\varepsilon}$ models (i.e., standard model, modified models with streamline curvature modification and/or preferential dissipation modification) are applied in order to analyze the turbulent flow of wall-attaching offset jet. For numerical convergence, this paper develops a method of slowly increasing the convective effect induced by skew-velocity in skew-upwind scheme (hereafter called Partial Skewupwind Scheme). Even though the method was simple, it was efficient in view of convergent speed, computer memory storage, programming, etc. The numerical results of all models show good prediction in first order calculations (i.e., reattachment length, mean velocity, pressure), while they show some deviations in ·second order (i.e., kinetic energy and its dissipation rate). Like the previous results obtained by upwind scheme, the streamline curvature modification results in better prediction, while the preferential dissipation modification does not.

2-方程式 모델 에 의한 二相亂流 제트流動 의 數値解析 (Calculation of Two-Phase Turbulent Jet with a Two-Equation Model)

  • 양선규;최영돈
    • 대한기계학회논문집
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    • 제9권6호
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    • pp.714-724
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    • 1985
  • 본 논문에서는 입자가 부상된 2상유동의 해석에서 여러유동조건의 유동을 공 통적으로 해석할 수 있고 또 유동의 난류구조를 규명할 수 있도록 하기 위해서 2-방정 식 난류모델을 적용하였고 또 지배방정식들 속에 나타나는 1유체와 2유체의 2차 상관 관계들을 모형화 할 때 Taweel and Landau의 스펙트럼 이론을 확장발전시켜 적용하였 다.

Level-Set 방법이 적용된 Flame Hole Dynamics 모델을 통한 난류 혼합층 확산화염 모사 (Simulation of a Diffusion Flame in Turbulent Mixing Layer by the Flame Hole Dynamics Model with Level-Set Method)

  • 김준홍;정석호;안국영;김종수
    • 한국연소학회:학술대회논문집
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    • 한국연소학회 2004년도 제28회 KOSCO SYMPOSIUM 논문집
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    • pp.102-111
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    • 2004
  • Partial quenching structure of turbulent diffusion flames in a turbulent mixing layer is investigated by the method of flame hole dynamics to develope a prediction model for the turbulent lift off. The present study is specifically aimed to remedy the problem of the stiff transition of the conditioned partial burning probability across the crossover condition by adopting level-set method which describes propagating or retreating flame front with specified propagation speed. In light of the level-set simulations with two model problems for the propagation speed, the stabilizing conditions for a turbulent lifted flame are suggested. The flame hole dynamics combined with level-set method yields a temporally evolving turbulent extinction process and its partial quenching characteristics is compared with the results of the previous model employing the flame-hole random walk mapping. The probability to encounter reacting' state, conditioned with scalar dissipation rate, demonstrated that the conditional probability has a rather gradual transition across the crossover scalar dissipation rate in contrast to the stiff transition of resulted from the flame-hole random walk mapping and could be attributed to the finite response of the flame edge propagation.

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