• 대한기계학회논문집B
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• 제28권9호
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• pp.1022-1031
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• 2004

The commutation errors by the filtering process in the large eddy simulation are considered. It is compared the conventional filter with the inhomogeneous filter that is devised to reduce the commutation errors. The weighting factor of the inhomogeneous filter suggested by Vasilyev is adopted. Also, using the optimizing function that estimates test filter width to eliminate the dissipations in the region excluding the vicinity of the wall, the flow patterns are analyzed. It is evaluated in simulations of the turbulent channel flow at Reynolds number of 1020, based on friction velocity and channel half height. Results show that the commutation errors can be significantly reduced by using the inhomogeneous filter and the optimized test filter width.

• 한국해양공학회지
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• 제24권6호
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• pp.41-50
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• 2010

This study established a 3D ecosystem model composed of stratification considering the topographic heat accumulation effect and river outflow, and then applied this model to Jinhae, Masan Bay. Specifically, it reenacted the formation and developmental process of ODW according to the stratification by calculating the kinematic eddy viscosity and eddy diffusion coefficient of the stratification model. The results were used as input data for the ecosystem model and compared with DO, COD, I-N, and I-P, which is the standard index of ocean water quality. As a result, it was determined that COD and T-N are third grade and T-P is second grade standards for a natural environment.

• 한국군사과학기술학회지
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• 제17권6호
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• pp.861-867
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• 2014

In the present study, the flow around a circular cylinder at $Re=3.6{\time}10^6$ is numerically simulated using URANS approach. The objective of this study is to evaluate the turbulence models(Realizable k-${\varepsilon}$, RNG k-${\varepsilon}$) through the prediction of the unsteady flow characteristics around the cylinder. The time-averaged drag coefficients and vortex shedding phenomenon in the wake region are compared to available experimental data and other numerical results. The simulation with Realizable k-${\varepsilon}$ model is found to be more dissipative due to large eddy viscosity predicted in the wake region while the simulation with RNG k-${\varepsilon}$ model predicts a complex vortex shedding phenomenon with more coherent structures realistically.

• 한국해안해양공학회지
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• 제8권3호
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• pp.256-267
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• 1996

연안 해수유동에 관한 3차원 수치모형의 적용에서 연직 과점성계수의 정확한 산정은 매우 중요하다. 본 연구에서는 연안 해수유동 계산시 널리 사용되고 있는 연직 과점성계수 산정방법들을 정상 개수로 흐름과 비정상류인 조류의 해석에 적용하여 수리실험자료와 비교평가하였다. 계산결과에 의하면, 정상류에 대해서는 비교된 모든 모형이 실험치와 대체로 일치하는 양호한 결과를 보였다. 그러나, 비정상류인 조류에 대해서는 난류 수송 방정식을 해석하는 2-방정식과 1-방정식 난류모형들은 대체로 실험치와 일치하는 결과를 주었으나, 0-방정식 모형은 난류의 수송현상을 제대로 고려하지 못하여 위상에서 실험치와 많은 차이를 보였다.

• Tribology and Lubricants
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• 제9권1호
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• pp.22-31
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• 1993

The thermohydrodynamic performance of large tilting pad journal bearings is analyzed, taking into account the three dimensional variation of lubricant viscosity. The eddy viscosity model based on wall formula is applied. The effects of temperature rise and turbulence on the bearing performance are studied in comparision with the isothermal or the laminar analysis. It is shown that these effects have significant influence on temperature distribution, load capacity and power loss of the bearing.

• Nuclear Engineering and Technology
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• 제55권9호
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• pp.3367-3382
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• 2023

Smoothed Particle Hydrodynamics (SPH) is a Lagrangian computational fluid dynamics method that has been widely used in the analysis of physical phenomena characterized by large deformation or multi-phase flow analysis, including free surface. Despite the recent implementation of eddy-viscosity models in SPH methodology, sophisticated turbulent analysis using Lagrangian methodology has been limited due to the lack of computational performance and numerical consistency. In this study, we implement the standard and dynamic Smagorinsky model and dynamic Vreman model as sub-particle scale models based on a weakly compressible SPH solver. The large eddy simulation method is numerically identical to the spatial discretization method of smoothed particle dynamics, enabling the intuitive implementation of the turbulence model. Furthermore, there is no additional filtering process required for physical variables since the sub-grid scale filtering is inherently processed in the kernel interpolation. We simulate lid-driven flow under transition and turbulent conditions as a benchmark. The simulation results show that the dynamic Vreman model produces consistent results with experimental and numerical research regarding Reynolds averaged physical quantities and flow structure. Spectral analysis also confirms that it is possible to analyze turbulent eddies with a smaller length scale using the dynamic Vreman model with the same particle size.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.19-23
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• 2010

초임계 환경에서 작동하는 액체 로켓 엔진의 케로신 스월 인젝터에서 케로신 물성치에 따른 인젝터 내외에서의 분사 특성을 연구하였다. 케로신의 물성치를 계산하기 위해 surrogate 모델이 적용되었다. 난류 수치 모델은 large eddy simulation을 기반으로 하였으며 SRK 상태 방정식, Chung의 기법을 포함하고 있다. 초임계 환경의 수치 해석 결과는 천이 임계 조건의 결과와 비교되었으며 스월 인젝터 내부의 액막과 중심부 사이의 밀도 및 점성 계수 분포의 차이가 관찰되었다.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 2002년도 춘계공동학술발표회요약집
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• pp.126-126
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• 2002

• 한국수자원학회논문집
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• 제44권6호
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• pp.461-470
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• 2011

Abrupt and gradual levee breach analyses on the flat domain were implemented by laboratory experiments and numerical simulations. To avoid the reflective wave from the side wall the experiment was performed in a large domain surrounded by waterway. A numerical model was developed for solving the two-dimensional gradual levee breach flow. The results of the numerical simulation developed in this study showed good agreement with those of the experimental data. However, even if the numerical schemes effectively replicated the trends of the observed water depth for the first shock, there were little differences for the second shock. In addition, even though the model considered the Smagorinsky horizontal eddy viscosity, the location and height of the hydraulic jump in the numerical simulation were not fairly well agree with experimental measurements. This shows the shallow water equation solver has a limitation which does not exactly reproduce the energy dissipation from the hydraulic jump. Further study might be required, considering the energy dissipation due to the hydraulic jump or transition flow from reflective wave.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.392-397
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• 2001

A numerical study is performed to investigate the interaction between subsonic axial turbine blade boundary layer and periodically oncoming rotor induced wakes. An implicit scheme for solving the compressible Navier-Stokes equation is developed, which adopts a 4th-order compact difference for spatial discretiztion, a 2nd order Crank-Nicolson scheme for temporal discretization and the dynamic eddy viscosity model as the subgrid scale model. The efficiency and the accuracy of the proposed method are verified by applying to some benchmark problems such as laminar cylinder flow, laminar airfoil cascade flow and a transitional flat plate boundary layer flow. Computational results show good agreements with previous experimental and numerical results. Finally, flow through a stator cascade is simulated at $Re = 7.5{\times}10^5$ without free-stream turbulence intensity. The velocity fields and skin friction coefficients in the transitional region show similar trends with previous boundary layer natural transition.