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리광훈,성형진,Rhee, Gwang-Hoon,Sung, Hyung-Jin 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.3
An unsteady numerical simulation was performed for locally-forced separated and reattaching flow over a backward-facing step. The local forcing was given to the separated and reattaching flow by means of a sinusoidally oscillating jet from a separation line. A version of the $k-{\varepsilon}-f_{\mu}$ model was employed, in which the near-wall behavior without reference to distance and the nonequilibrium effect in the recirculation region were incorporated. The Reynolds number based on the step height (H) was fixed at $Re_H=33000$, and the forcing frequency was varied in the range $0{\leq}St_H{\leq}2$. The predicted results were compared and validated with the experimental data of Chun and Sung. It was shown that the unsteady locally-forced separated and reattaching flows are predicted reasonably well with the $k-{\varepsilon}-f_{\mu}$ model. To characterize the large-scale vortex evolution due to the local forcing, numerical flow visualizations were carried out.
난류박리 및 재부착 유동에 대한 저레이놀즈수 비선형 열전달 모형의 개발
리광훈,성형진,Rhee, Gwang-Hoon,Sung, Hyung-Jin 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.2
A nonlinear low-Reynolds-number heat transfer model is developed to predict turbulent flow and heat transfer in separated and reattaching flows. The $k-{\varepsilon}-f_{\mu}$ model of Park and Sung (1997) is extended to a nonlinear formulation, based on the nonlinear model of Gatski and Speziale (1993). The limiting near-wall behavior is resolved by solving the $f_{\mu}$ elliptic relaxation equation. An improved explicit algebraic heat transfer model is proposed, which is achieved by applying a matrix inversion. The scalar heat fluxes are not aligned with the mean temperature gradients in separated and reattaching flows; a full diffusivity tensor model is required. The near-wall asymptotic behavior is incorporated into the $f_{\lambda}$ function in conjunction with the $f_{\mu}$ elliptic relaxation equation. Predictions of the present model are cross-checked with existing measurements and DNS data. The model preformance is shown to be satisfactory.
공동주택의 공기환기시스템의 변화에 따른 국소급기지수 특성의 수치적 연구
리광훈,문종민 한국실내환경학회 2011 한국실내환경학회지 Vol.8 No.2
Recently, the air pollution have bad effects on the indoor environment. Many buildings around the world use natural ventilation. to remove the air pallutant. But, nowadays, ventilation requirements can be demanding, as modern systems require greatly improved reliability and control. The fan and the duct are used to remove air mechanically from the space. Until now, apartment houses have been relying on the duct supply system ventilation rather than other system ventilations. Therefore, the establishment of a prediction method based on optimal ventilation energy consumption using duct supply system and ductless is the ultimate goal of this study. As a result, this study found that the characteristics of duct and ductless supply system ventilation are dependent to each exhaust system. Consequently, the local supply indices of the duct supply system is definitely superior about 24.6% ~ 26.4 % than those of ductless supply system. However, the duct supply system has greater pressure drop in ventilation area than ductless, and duct system needs a lot of ventilation energy. In this study, The ductless supply system has advantage over the duct system about 14.8 % as duct exhaust system and 20.0% as ductless exhaust system in terms of modified local supply indices.
입구 유동 가진에 의한 사각 발열체 주위의 유동제어 및 열전달촉진 (I) 유동장 수치해석
리광훈,김서영,성형진 대한설비공학회 2002 설비공학 논문집 Vol.14 No.7
The characteristics of a pulsating flow field from a heated block representing heat-dissipating electronic component in a channel have been numerically investigated. At the channel inlet a pulsating sinusoidal flow is imposed. The Reynolds number based on the channel height (H) is fixed at Re=500, and the forcing frequency is varied in the range of $0\leqSt\leq2$. Numerical results on the time-dependent flow field are obtained and averaged over a cycle of pulsation. The effect of the important governing parameters such as the Strouhal number is investigated in detail. The results indicate that the recirculating flow behind the block is substantially affected by the pulsation frequency. To characterize the periodic vortex shedding due to the inflow pulsation, numerical flow visualizations are carried out.