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On Constructing an Explicit Algebraic Stress Model Without Wall-Damping Function
Noma Park,Jung Yul Yoo 대한기계학회 2002 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.16 No.11
In the present study, an explicit algebraic stress model is shown to be the exact tensor representation of algebraic stress model by directly solving a set of algebraic equations without resort to tensor representation theory. This repeals the constraints on the Reynolds stress, which are based on the principle of material frame indifference and positive semi-definiteness. An a priori test of the explicit algebraic stress model is carried out by using the DNS database for a fully developed channel flow at Rer = 135. It is confirmed that two-point correlation function between the velocity fluctuation and the Laplacians of the pressure-gradient i s anisotropic and asymmetric in the wall-normal direction. Thus, a novel composite algebraic Reynolds stress model is proposed and applied to the channel flow calculation, which incorporates non-local effect in the algebraic framework to predict near-wall behavior correctly.<br/>
On Constructing an Explicit Algebraic Stress Model Without Wall-Damping Function
Park, Noma,Yoo, Jung-Yul The Korean Society of Mechanical Engineers 2002 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.16 No.11
In the present study, an explicit algebraic stress model is shown to be the exact tensor representation of algebraic stress model by directly solving a set of algebraic equations without resort to tensor representation theory. This repeals the constraints on the Reynolds stress, which are based on the principle of material frame indifference and positive semi-definiteness. An a priori test of the explicit algebraic stress model is carried out by using the DNS database for a fully developed channel flow at Rer = 135. It is confirmed that two-point correlation function between the velocity fluctuation and the Laplacians of the pressure-gradient i s anisotropic and asymmetric in the wall-normal direction. Thus, a novel composite algebraic Reynolds stress model is proposed and applied to the channel flow calculation, which incorporates non-local effect in the algebraic framework to predict near-wall behavior correctly.
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.
Virtual design on the heat pump refrigeration cycle: challenges and approaches
황윤제,Park Noma 대한설비공학회 2024 International Journal of Air-Conditioning and Refr Vol.32 No.1
Virtual product design (VPD) of the refrigeration cycle has long been a major subject of many engineers and manufacturers. Issues should be the question of how simulation gets close to the real world in virtual ways. It is especially true when we consider variable refrigerant flow (VRF) heat pumps, having various types of indoor unit combinations, long and complicated piping configurations, and simultaneous cooling and heating functions under extreme weather conditions. In this regard, model-based systems engineering (MBSE) or model-based design (MBD) guides a methodology to make a virtual model easily. Now, there are plenty of engineering platforms and tools to make a strong simulation model, which provides interfacing technology among multiple physics, different dimensions, and codes in different languages. In the study, the authors share their experience in the virtual design for a VRF heat pump system including the architecture, multiple physics, and the connection with the control SW. Modelica, an acausal and object-oriented modeling language, constructs the backbone of the model to describe the dynamic behavior of refrigerants and to combine external components in the form of functional mock-up units (FMUs). The developed virtual model is validated against measured data, showing it can reproduce all the essential physics of interest both in qualitative and quantitative ways.