• 한국연소학회:학술대회논문집
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• 한국연소학회 2002년도 제25회 KOSCI SYMPOSIUM 논문집
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• pp.11-17
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• 2002

The first-order conditional moment closure (CMC) model is applied to $CH_4$/Air turbulent jet diffusion flames(Sandia Flame D, E and F). The flow and mixing fields are calculated by fast chemistry assumption and a beta function pdf for mixture fraction. Reacting scalar fields are calculated by elliptic CMC formulation. The results for Flame D show reasonable agreement with the measured conditional mean temperature and mass fractions of major species, although with discrepancy on the fuel rich side. The discrepancy tends to increase as the level of local extinction increases. Second-order CMC may be needed for better prediction of these near-extinction flames.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2006년도 제32회 KOSCO SYMPOSIUM 논문집
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• pp.111-120
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• 2006

The fully coupled conditional moment closure(CMC) model has been developed to realistically simulate the structure of complex turbulent nonpremixed syngas flame, in which the flame structure could be considerablyl influenced by the turbulence, transport history, and heat transfer as well. In order to correctly account for the transport effect, the CMC transport equations fully coupled with the flow and mixing fields are numerically solved. The present CMC approach has successfully demonstrated the capability to realistically predict the detailed structure and the overall combustion characteristics. The numerical results obtained in this study clearly reveal the importance of the convective and radiative heat transfer in the precise structure and NOx emission of the present confined combustor with a cooling wall.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년도 제31회 추계학술대회논문집
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• pp.330-333
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• 2008

본 논문에서는 그동안 부산대학교 연소추진연구실에서 진행되어 온 스크램제트 엔진 내의 초음속 연료 공기 혼합 및 난류 연소 연구 결과에 대한 소개가 이루질 것이다. 아울러 실용 스크램제트 엔진에서 이용되는 초임계 탄화 수소 연료 연소의 특징과 수치적 모델링 기법에 대하여 소개가 잇을 것이다.

• Journal of the Korean Wood Science and Technology
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• 제25권2호
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• pp.33-44
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• 1997

This study was executed to examine the effects of polypropylene fiber length and process variables of the composites made from wood fiber and nonwood fiber mixed formulations. As a nonwood fiber the polypropylene with 3 denier thickness of tow condition was selected and cut into each length of 0.5, 1.0, 1.5, 2.0 and 2.5cm to mix with wood fiber. And also western hemlock wood fiber for medium density fiberboard was prepared. First, to decide an adequate polypropylene mixing fiber length, the composites of 1.0g/$cm^3$ density were made from 10% polypropylene fiber by each of five lengths and 90% western hemlock fiber mixed formulations. Thereafter as the experiments of process variable, the composites applied with adequate polypropylene fiber length(1.5cm) were made from 4 density levels (0.6, 0.8, 1.0, 1.2g/$cm^3$). 3 mixed formulations of wood fiber to polypropylene fiber(95 : 5, 90 : 10, 85 : 15), and 3 mat moisture contents(5, 10, 20%). According to the results and discussions it was concluded as follows ; The physical and mechanical properties were shown improved tendency. as polypropylene fiber length was increased in the range from 0.5 to 1.5cm, but shown decreasing tendency from 2.0 to 2.5 cm. Accordingly, it was shown that polypropylene fiber length is limited to 1.5cm or less length in mixing wood fiber and polypropylene fiber by turbulent air mixing process. As the densities of wood fiber-polypropylene fiber composites were increased, the physical and mechanical properties were clearly improved. Also they were shown significantly increasement statistically between densities respectively. In the mixed formulations, physical and mechanical properties were shown only slightly improvement, as they changed from 95 : 5 to 85 : 15 in wood fiber to polypropylene fiber. Despite of increasement of mat moisture content, mechanical properties were not improved significantly but physical properties were improved somewhat in wood fiber-polypropylene fiber composites.

• 한국항공우주학회지
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• 제31권3호
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• pp.8-14
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• 2003

난류혼합층에서 속도비 변화에 따른 입자의 운동형태에 대하여 수치해석적 연구를 수행하였다. Turbulent closure를 목적으로 Subgrid모델을 바탕으로 한 LES를 적용하여고 입자 운동을 해석하기 위해 Lagrangian 방법을 적용하였다. 입자의 직경이 10, 50, 100, 150, 200${\mu}m$인 입자들이 분리판 끝단에서 정지한 상태로 혼합층에 유입이 되고, 큰-크기 와류구조에 영향을 받아 혼합층 내로 확산이 되어진다. 혼합층의 성장특성은 속도비 변화에 매루 민감하여, 입자의 확산은 혼합층의 속도비와 입자 직경의 변화에 따라 거동을 달리함을 알 수 있었다. 또한 Stokes 수와 입자확산의 관계를 나타내었다. 그 결과로 St~1인 경우 입자의 확산이 유동장의 확산보다 빠르게 일어나나, St<<1과 St>>1인 경우는 입자의 확산이 잘 일어나지 않음을 알 수 있다.

• 대한토목학회논문집
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• 제13권2호
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• pp.267-277
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• 1993

본 논문에서는 유한요소법을 2차원 난류경계층에 적용하였으며, 점성유체의 시간의존 비압축성 운동을 시간과 압력장(場)에서 Navier-Stokes방정식과 vorticity방정식을 이용하여 정식 화하였다. 수치계산방법은 Galerkin방법에 기초하였으며, 난류 경계층의 eddy kinematic viscosity에 대해서는 Prandtl의 혼합거리이론을 도입하였다. 난류 경계층에서 파동에 의한 임의 저면에서 저질의 이동을 수치계산하였다. 유한 요소법에 의해 얻어진 결과는 진동흐름에 의한 경계층과 파동에 의한 경계층에서의 특성의 차이를 분명히 하였다.

• 대한기계학회논문집
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• 제19권5호
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• pp.1340-1350
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• 1995

The effects of thermal stratification on the flow past a heated circular cylinder with various heating rates were examined in a wind tunnel. Turbulent intensities, r.m.s.values of temperature and turbulent convective heat flux distributions in the cylinder wakes with and without thermal stratification were measured by using a hot-wire and cold-wire combination probe. The phase averaging method was also used to estimate coherent contributions to the turbulent flow field in the near wake. The results show that the scalar mixing process is very different according to the mean temperature fields especially in the upper part of the wake. The coherent structure of the temperature field makes a large contribution to the time mean value like velocity components. However, the coherency of the temperature fluctuation is very different with the change of mean temperature fields, though the velocity coherent motions are quite similar in all experimental conditions.

• 한국해양학회지
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• 제12권1호
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• pp.7-12
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• 1977

Vertical mixing in the ocean affects the formation of water masses as well as the vertical distribution of nutrients and dissolved substances. this study is to investigate the effect of stability on the intensity of vertical transfer in the case of shallow and straitfied channel. It is found that the relation of the stability and vertical turbulent diffusion is given by K$\sub$z/ = -${\beta}$-(c+${\beta}$) / ${\alpha}$(E-1/${\alpha}$) where K$\sub$z/ and E denotes the vertical turbulent diffusion coefficient and stability, respectively. The empirical coefficients ${\alpha}$, ${\beta}$ and c depend on the magnitude of vertical components and stability, i.e., through thermocline intensity. The study indicates that the diffusivity of the surface mixed layer is (K$\sub$z/)=300∼1,200$\textrm{cm}^2$/sec, the thermocline layer is (K$\sub$z/)= 50∼200$\textrm{cm}^2$/sec and the cold layer is (K$\sub$z/)=200∼600$\textrm{cm}^2$/sec based on near- minimum least-squares error estimates from the regression analysis. An important result of our study comes out that the model is in accordance with the general trends of the effect of stability on the vertical turbulent diffusion coefficients in the case of shallow and strongly stratified channel.

• 한국자동차공학회논문집
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• 제11권6호
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• pp.51-58
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• 2003

A cycle simulation method is developed by coupling a commercial code, Ricardo's WAVE, with the SENKIN code from CHEMKIN packages to predict combustion characteristics of an HCCI engine. By solving detailed chemical kinetics the SENKIN code calculates the combustion products in the combustion chamber during the valve closing period, i.e. from IVC to EVO. Except the combustion chamber during the valve closing period the WAVE code solves thermodynamic status in the whole engine system. The cycle simulation of the complete engine system is made possible by exchanging the numerical solutions between the codes on the coupling positions of the intake port at IVC and of the exhaust port at EVO. This method is validated against the available experimental data from recent literatures. Auto ignition timing and cylinder pressure are well predicted for various engine operating conditions including a very high ECR rate although it shows a trend of sharp increase in cylinder pressure immediate after auto ignition. This trend is overpredicted especially for EGR cases, which may be due to the assumption of single-zone combustion model and the limit of the chemical kinetic model for the prediction of turbulent air-fuel mixing phenomena. A further work would be needed for the implementation of a multi-zone combustion model and the effect of turbulent mixing into the method.

• Ocean Science Journal
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• 제43권2호
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• pp.81-90
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• 2008

A study of estuarine flows during a neap tide was performed using 13-hour roving acoustic Doppler current profiles (ADCP) and conductivity-temperature-depth (CTD) profiles in the Altamaha River estuary, Georgia, U.S.A. The least-squared harmonic analysis method was used to fit the tidal ($M_2$) component and separate the flow into two components: the tidal and residual ($M_2$-removed) flows. We applied this method to depth-averaged data. Results show that the $M_2$ component demonstrates over 95% of the variability of observation data. As the flow was dominated by the $M_2$ tidal component in a narrow channel, the tidal ellipse distribution was essentially a back-and-forth motion. The amplitude of $M_2$ velocity component increased slightly from the river mouth (0.45 m/sec) to land (0.6 m/sec) and the phase showed fairly constant values in the center of the channel and rapidly decreasing values near the northern and southern shoaling areas. The residual flow and transport calculated from depth-averaged flow shows temporal variability over the tidal time scale. Strong landward flows appeared during slack waters which may be attributed to increased baroclinic forcing when turbulent mixing decreases.