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LES 에서 중심 및 상류 컴팩트 차분기법의 적합성에 관하여(Ⅰ)
박노마(Noma Park),유정열(Jung Yul Yoo),최해천(Haecheon Choi) 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.7
The suitability of high-order accurate, centered and upwind-biased compact difference schemes is evaluated for large eddy simulation of turbulent flow. Two turbulent flows are considered: turbulent channel flow at Re = 23000 and flow over a circular cylinder at Re = 3900. The effects of numerical dissipation on the finite differencing and aliasing errors and the subgrid-scale stress are investigated. It is shown through the simulations that compact upwind schemes are not suitable for LES, whereas the fourth order-compact centered scheme is a good candidate for LES provided that proper dealiasing of nonlinear terms is performed. The classical issue on the aliasing error and the treatment of nonlinear terms is revisited with compact difference schemes.<br/>
국내 현장 기반 공기열원 축열식 열펌프의 계절 성능에 대한 연구
박노마 (Noma Park),박희웅(Heewoon Park),정승현(Seunghyun Jung),신정섭(Jeongseob Shin),정백영(Baikyoung Chung),정훈(Hoon Jung) 대한설비공학회 2012 대한설비공학회 학술발표대회논문집 Vol.2012 No.6
In this paper, the optimal inverter operations for cascade AWHPs integrated with thermal energy storage are investigated, which will be the replacement of electric boiler using cheap midnight electricity tariff. It is shown that the optimal target high pressure for the outdoor unit has significant influence in enhancing the efficiency yielding 32% reduction of power consumption. From field monitoring data, it is expected that the yearly running cost and electricity consumption saving over the current electric boiler is about 57% per household. Thus, the replacement of current heater boiler with heat pump is a win-win game for both customers and KEPCO provided that proper subsidies are given to customers to reduce otherwise high initial cost.
착상 및 제상을 포함한 VRF 히트펌프의 동적 수치해석 모델
박노마,신정섭,정백영,김병순,Park, Noma,Shin, Jeong Seob,Chung, Baik Young,Kim, Byung Soon 대한기계학회 2015 대한기계학회 논문집. Transactions of the KSME. C, 산업기술과 혁신 Vol.3 No.1
실외 열교환기의 착상 및 제상조건 하에서 VRF 멀티형 히트펌프의 동적 거동의 해석을 위한 시뮬레이션 기법이 제안되었다. 이를 위해 열전달-물질전달 완벽 상사 가정에 기반한 간단한 착상모델과 제상 모델이 제안되었다. 제안된 착제상 모델은 용량가변 압축기 모델과, 미소면적에 대한 열 및 모멘텀 평형에 근거한 열교환기 모델을 채택한 동적 사이클 해석모델에 적용되었다. 따라서, 제안된 모델은 공간에 대해 비균질 착상을 자연스럽게 예측할 수 있다. 개발된 동적 사이클 해석 모델은 실험결과와 비교하여 능력 및 효율을 10% 이내에서 잘 예측함을 확인하였다. 최종적으로, 개발된 모델은 표준적인 건물의 난방시즌 운전 해석에 적용되었으며, 착상 및 제상으로 인하여 동절기의 계절 성능계수를 7% 가량 하락 시킴을 보일 수 있었다. In this study, a new dynamic VRF-type heat pump simulation model is proposed which incorporates frosting and defrosting models. Toward this end, a simple frosting model based on the perfect analogy, and lumped system based defrost model, are proposed. Then, frosting and defrosting models are incorporated into a dynamic heat pump model which adopts segment-by-segment local heat exchanger model and map-based variable speed compressor model. Thus, the model can naturally represent locally uneven frosting and defrosting on the heat exchanger surface. Developed simulation model is validated against available experimental data to show good agreement within 10% error for capacity and COP. Finally, developed dynamic heat pump model is applied to annual heating season simulation to show that seasonal COP of heat pump is degraded by 7% due to frosting and defrosting.
A Dynamic Globalization Model for Large Eddy Simulation of Complex Turbulent Flow
Haecheon Choi(최해천),Noma Park(박노마),Jinseok Kim(김진석) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
A dynamic subgrid-scale model is proposed for large eddy simulation of turbulent flows in complex geometry. The eddy viscosity model by Vreman [Phys. Fluids, 16, 3670 (2004)] is considered as a base model. A priori tests with the original Vreman model show that it predicts the correct profile of subgrid-scale dissipation in turbulent channel flow but the optimal model coefficient is far from universal. Dynamic procedures of determining the model coefficient are proposed based on the 'global equilibrium' between the subgrid-scale dissipation and viscous dissipation. An important feature of the proposed procedures is that the model coefficient determined is globally constant in space but varies only in time. Large eddy simulations with the present dynamic model are conducted for forced isotropic turbulence, turbulent channel flow and flow over a sphere, showing excellent agreements with previous results.
원형 실린더를 지나는 난류 유동장의 직접수치해석과 큰 에디모사를 위한 스케일 간 상호작용 연구
김택근(Taekkeun Kim),박노마(Noma Park),유정열(Jung Yul Yoo) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
Stochastic nature of subgrid-scale stress causes the predictability problem in large eddy simulation (LES) by which the LES solution field decorrelates with field from filtered direct numerical simulation (DNS). In order to evaluate the predictability limit in a priori sense, the information on the interplay between resolved scale and subgrid-scale (SGS) is required. In this study, the analysis on the inter-scale interaction is performed by applying tophat and cutoff filters to DNS database of flow over a circular cylinder at Reynolds number of 3900. The effect of filter shape is investigated on the interpretation of correlation between scales. A critique is given on the use of tophat filter for SGS analysis using DNS database. It is shown that correlations between Karman vortex and SGS kinetic energy drastically decrease when the cutoff filter is used, which implies that the small scale universality holds even in the presence of the large scale coherent structure.