• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2005년도 제25회 추계학술대회논문집
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• pp.450-454
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• 2005

축대칭 동축형 램제트 연소기에 대한 반응 유동장 해석을 수행하였다. 2차원 축대칭 Wavier-Stokes 방정식과 낮은 레이놀즈 수 $k-\varepsilon$ 난류 모델을 이용하였고, 유한반응률 화학반응 모델을 적용하였다. 난류 연소 모델인 EDM (Eddy-Dissipation Model)과 층류 반응 모델을 적용한 경우를 서로 비교하였다. 급확대 연소기와 wedge형 보염기를 장착한 동축형 램제트 연소기에 대한 반응 유동장 수치해석을 통해 두 가지 결과를 화염안정 측면에서 서로 비교하였다.

• 대한기계학회논문집B
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• 제22권5호
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• pp.685-697
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• 1998

Series of recent k-.epsilon. model modification have been carried out with the aid of DNS data to include the effect of near wall. Though these methods opened new way of turbulence modelings, newly developed turbulence models of its kind had yet shortcomings in prediction for the turbulent flows with various Reynolds numbers and various geometric conditions. As a remedy for these shortcomings, a new k-.epsilon. model proposed here by improving the dissipation rate equation and the damping function for eddy viscosity model. The new dissipation rate equation was modeled based on the energy spectrum and magnitude analysis. The damping function for eddy viscosity was also formulated on the ground of distribution of dissipation rate length scales near a wall and the DNS data. The new k-.epsilon. model was applied to the fully developed turbulent flows in a channel and a pipe with a wide range of Reynolds numbers. Prediction results showed that the present model represents properly the turbulence properties in all turbulent regions over a wide range of Reynolds numbers.

• 한국해양학회지:바다
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• 제12권4호
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• pp.390-399
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• 2007

하계 동중국해 북부 대륙붕 해역에서 해수 혼합을 연구하기 위하여 2005년 8월과 2006년 8월에 한국해양연구원 연구선 이어도호를 이용하여 해수 물성 및 난류 관측을 수행하였다. 유속 변형으로부터 산출한 난류운동에너지 소산율은 표층에서 $10^{-7}{\sim}10^{-4}$, 저층에서 $10^{-7}{\sim}10^{-6}$와 수온약층에서 $10^{-7}$ W/kg의 높은 값이 나타났다. 관측 자료는 표층의 경우 바람에 의해 지속적으로 혼합이 이루어짐을 보여주었다. 수온약층 하부에서의 높은 소산율은 내부파의 영향으로 판단된다. 저층의 높은 소산율은 저층의 탁도 분포의 경향과 일치하여 조류에 의한 해저면층 교란의 결과임을 시사해주었다. 바닥에서의 연직확산계수는 낮은 안정도와 높은 난류상태의 복합적인 영향으로 $10^{-3}{\sim}10^{-2}m^2/s$로 높은 값이 나타났다.

• Journal of Mechanical Science and Technology
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• 제20권2호
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• pp.262-270
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• 2006

Direct numerical simulations (DNS) of turbulent channel flows up to $Re_{\tau}=1270$ are performed to investigate an elliptic feature and strain rate field on cross sections of coherent fine scale eddies (CFSEs) in wall turbulence. From DNS results, the CFSEs are educed and the strain rate field around the eddy is analyzed statistically. The principal strain rates (i.e. eigenvalues of the strain rate tensor) at the CFSE centers are scaled by the Kolmogorov length $\eta$ and velocity $U_k$. The most expected maximum (stretching) and minimum (compressing) eigenvalues at the CFSE centers are independent of the Reynolds number in each $y^+$ region (i. e. near-wall, logarithmic and wake regions). The elliptic feature of the CFSE is observed in the distribution of phase-averaged azimuthal velocity on a plane perpendicular to the rotating axis of the CFSE $(\omega_c)$. Except near the wall, phase-averaged maximum $(\gamma^{\ast}/\gamma_c^{\ast})$ and minimum $(\alpha^{\ast}/\alpha_c^{\ast})$ an eigenvalues show maxima on the major axis around the CFSE and minima on the minor axis near the CFSE center. This results in high energy dissipation rate around the CFSE.

• 대한기계학회논문집B
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• 제33권12호
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• pp.1014-1021
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• 2009

A new eddy viscosity equation was formulated from assumption of turbulence length scale equation and specific dissipation ratio equation. Then, a set of turbulence model equations for the turbulent kinetic energy ${\kappa}$, the viscosity ${\nu}_t$, and the intermittency factor ${\gamma}$ is proposed by considering the entrainment effect. Closure coefficients are determined by experimental data and resorting to numerical optimization. Present model has been applied to compute four representative cases of free shear flows and successfully compared with experimental data. In particular, the spreading rate, the centreline mean velocity and the profiles of intermittency are calculated with improved accuracy. Also, the proposed ${\nu}_t-{\kappa}-{\gamma}$ model was applied to channel flow by considering the wall effect and the results show good agreements with the Direct Numerical Simulation data.

• 한국항공운항학회지
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• 제17권2호
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• pp.1-7
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• 2009

This paper illustrates how simulation modeling can be of substantial help in designing constructions in the vicinity of airport runway and presents results about the influence of aircraft wake vortices through computer simulation. The cross-wind energy dissipation rate is estimated from the Y-directional velocity spectrum for a sample in a real meteorological observation data. The eddy region about cross wind in the vicinity of airport runway is highly dependent on the height and shape of the buildings and the AOA of aircraft is greatly influenced by Y-directional velocity occurred by dint of separation region in runway.

• 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.

• International Journal of Aeronautical and Space Sciences
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• 제16권4호
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• pp.560-570
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• 2015

We present a simulation of a hybrid Reynolds-averaged Navier Stokes / Large Eddy Simulation (RANS/LES) based on detached eddy simulation (DES) for a Burrows and Kurkov supersonic planar mixing experiment. The preliminary simulation results are checked in order to validate the numerical computing capability of the current code. Mesh refinement studies are performed to identify the minimum grid size required to accurately capture the flow physics. A detailed investigation of the turbulence/chemistry interaction is carried out for a nine species 19-step hydrogen-air reaction mechanism. In contrast to the instantaneous value, the simulated time-averaged result inside the reactive shear layer underpredicts the maximum rise in $H_2O$ concentration and total temperature relative to the experimental data. The reason for the discrepancy is described in detail. Combustion parameters such as OH mass fraction, flame index, scalar dissipation rate, and mixture fraction are analyzed in order to study the flame structure.

• KEPCO Journal on Electric Power and Energy
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• 제5권3호
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• pp.189-195
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• 2019

논문에서는 상용급 가스터빈을 대상으로 해서 셰일가스를 연료로 공급할 때 유동 및 연소특성을 3-D 수치해석적 방법으로 구하였다. 이 때, Standard k-e 난류모델, 2단 메탄산화반응, Finite rate/Eddy dissipation 반응모델, DTRM 복사모델이 사용되었고, 기준조건(도시가스, PR 0.07)에서 출구 측에서 형성되는 온도는 이전 문헌 값과 비슷한 값을 보였다. 위 모델을 바탕으로 해서 연료조건으로 기존의 도시가스 외에 세 가지 셰일가스 조건(도시가스 대비 열량기준 80%, 90%, 105%)을 선정하였고, 각 연료조건에 대하여 세 가지 연료분사조건(PR=0.7, 0.9, 0.11)에 대한 해석을 수행하였다. 해석결과, 모든 셰일가스 연료공급 조건에 대하여 도시가스 대비 온도 혹은 NOx 측면에서 연소안정화를 만족하였다. 또한 모든 조건에 대해서 PR이 증가할수록 출구측 평균온도는 일정했지만 NOx량은 증가하였다. 이는 파일럿비가 증가할수록 상대적으로 확산연소가 증가했기 때문이다.

• 한국연소학회지
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• 제20권3호
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• pp.35-42
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• 2015

Investigating coal combustion in a large-scale boiler using computational fluid dynamics (CFD) requires a combination of flow and reaction models. These models include a number of rate constants which are often difficult to determine or validate for particular coals or furnaces. Nonetheless, CFD plays an important role in developing new combustion technologies and improving the operation. In this study, the model selection and rate constants for coal devolatilization, char conversion, and turbulent reaction were evaluated for a commercial wall-firing boiler. The influence of devolatilization and char reaction models was found not significant on the overall temperature distribution and heat transfer rate. However, the difference in the flame shapes near the burners were noticeable. Compared to the coal conversion models, the rate constant used for the eddy dissipation rate of gaseous reactions had a larger influence on the temperature and heat transfer rate. Based on the operation data, a value for the rate constant was recommended.