• Nuclear Engineering and Technology
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• 제16권1호
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• pp.21-28
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• 1984

수치확산을 포함한 truncation오차의 줄임은 수치해석의 중요한 과제가 되어왔다. Stream line방법이 교차수치 확산과 비확산형의 truncation 오차를 제거하기 위하여 고안되었다. 또한, stream line방법과 유한 차분법이 합쳐진 2단계 stream line방법이 비압축성 난류유동의 지배 방정식을 풀기 위하여 고안되었다. 이 방법은 유한 차분법과 비교되었으며, 두 방법 모두 실험자료와 비교되었다. 그리고, 두 방법의 truncation 오차를 비교하기 위하여 truncation 오차 분석이 행해졌다

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2002년도 춘계 학술대회논문집
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• pp.8-15
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• 2002

For the large scale computation of turbulent flows around an arbitrarily shaped body, a parallel LES (large eddy simulation) code has been recently developed in which domain decomposition method is adopted. METIS and MPI (message Passing interface) libraries are used for domain partitioning and data communication between processors, respectively. For unsteady computation of the incompressible Wavier-Stokes equation, 4-step splitting finite element algorithm [1] is adopted and Smagorinsky or dynamic LES model can be chosen fur the modeling of small eddies in turbulent flows. For the validation and performance-estimation of the parallel code, a three-dimensional laminar flow generated by natural convection inside a cube has been solved. Then, we have solved the turbulent flow around MIRA (Motor Industry Research Association) model at $Re = 2.6\times10^6$, which is based on the model height and inlet free stream velocity, using 32 processors on IBM SMP cluster and compared with the existing experiment.

• 대한기계학회논문집B
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• 제28권7호
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• pp.879-886
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• 2004

A numerical optimization has been carried out to determine the shape of the three-dimensional channel with oblique ribs attached on both walls to enhance turbulent heat transfer. The response surface based optimization is used as an optimization technique with Reynolds-averaged Navier-Stokes analysis of fluid flow and heat transfer. Shear stress transport (SST) turbulence model is used as a turbulence closure. Numerical results fur heat transfer rate show good agreements with experimental data. four dimensionless variables such as, rib pitch-to-rib height ratio, rib height-to-channel height ratio, streamwise rib distance on opposite wall to rib pitch ratio, and the attack angle of the rib are chosen as design variables. The objective function is defined as a linear combination of heat-transfer and friction-loss related coefficients with a weighting factor. D-optimal method is used to determine the training points as a means of design of experiment. Sensitivity of the objective parameters to each design variable has been analyzed. And, optimal values of the design variables have been obtained in a range of the weighting factor.

• 한국추진공학회지
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• 제5권3호
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• pp.33-40
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• 2001

본 연구에서는 초음속 증기 이젝터의 작동특성을 조사하기 위하여 압축성 축대칭 Navier-Stokes 방정식의 수치계산을 행하였다. 2차 유동측의 압력 및 배압을 변화시켜 이들 압력이 혼입유량에 미치는 영향을 조사하였다. 연구의 결과로부터 초음속 증기 이젝터에서 2차 유동측 압력 및 배압은 임계 혼입유량에 상당한 영향을 미치며, 1차구동노즐의 형상과 2차유동의 압력이 주어지는 경우 임계혼입 유량비를 예측할 수 있음을 알았다. 수치계산 결과는 실험에서 얻은 임계혼입유량비를 잘 예측하였다.

• 한국추진공학회지
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• 제4권4호
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• pp.70-77
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• 2000

초음속 2단벨노즐(SDBN)은 종래의 축소확대형 초음속 노즐의 벽면에 변곡점을 설치하여, 비행체의 고도에 따른 노즐내부의 유동특성을 조절하기 위한 새로운 개념의 추진노즐이다. 본 연구에서는 이러한 SDBN의 유용성과 유동특성을 조사하기 위하여 축대칭 Navier-Stokes 방정식을 유한체적법으로 수치계산하였다. 본 연구의 결과로부터 SDBN의 Base 노즐의 길이는 SDBN 내부에서 발생하는 충격파 시스템에 영향을 미칠 뿐만 아니라, 노즐 유동의 박리위치가 변곡점에 고착되는 넓은 범위의 압력비가 존재한다는 것을 알았다. 또 SDBN의 최대추력은 노즐출구에서 유동이 적정팽창 상태일 때 발생한다는 것을 알았다.

• 대한기계학회논문집B
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• 제30권7호
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• pp.622-629
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• 2006

The shape optimization of blade sweep in a transonic axial compressor rotor of NASA Rotor 37 has been performed using response surface method and the three-dimensional Wavier-Stokes analysis. Two shape variables of the rotor blade, which are used to define the rotor sweep, are introduced to increase the adiabatic efficiency of the compressor. Throughout the optimization, optimal shape having a backward sweep is obtained. Adiabatic efficiency, which is the objective function of the present optimization, is successfully increased. Separation line due to the interference between a shock and surface boundary layer on the blade suction surface is moved downstream for the optimized blade compared to the reference one. The increase in adiabatic efficiency for the optimized blade is caused by suppression of the separation due to a shock on the blade suction surface.

• 대한기계학회논문집B
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• 제30권7호
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• pp.700-706
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• 2006

This study presents a numerical procedure to optimize the shape of dimple surface to enhance turbulent heat transfer in a rectangular channel. The response surface based optimization method is used as an optimization technique with Reynolds-averaged Wavier-Stokes analysis of fluid flow and heat transfer with shear stress transport (SST) turbulence model. The dimple depth-to-dimple print diameter ratio, channel height-to-dimple print diameter ratio, and dimple print diameter-to-pitch ratio are chosen as design variables. The objective function is defined as a linear combination of heat transfer related term and friction loss related term with a weighting factor. full factorial method is used to determine the training points as a mean of design of experiment. The optimum shape shows remarkable performance in comparison with a reference shape.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2000년도 추계 학술대회논문집
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• pp.46-53
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• 2000

To improve the performance at all design points, multi-point optimization method is implemented for the nose fairing shape design of space launcher. The response surface method is used to effectively reduce the huge computational loads during the optimization process. The drag is selected as the objective function, and the surface heat transfer characteristics, and the internal volume of the nose fairing ate considered as design constraints. Full Wavier-Stokes equations are selected as governing equations. Two points drag minimization, and two points drag / heat flux optimization were successfully performed and configurations which have good performance for the wide operation range were derived. By considering three design points, the space launcher shape which undergoes the least drag during whole flight mission was designed. For all the design cases, the constructed response surfaces show good confidence level with only 23 design points with the proper stretching of the design space.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2000년도 추계 학술대회논문집
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• pp.141-148
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• 2000

The discrete noise of the cross-flow fan with uniform/random pitch blades is predicted by computational methods. With the time dependent surface pressure data obtained by solving the Wavier-Stokes equation, the acoustic pressure is calculated by the Ffowcs Williams-Hawkings equation. The positions of the blade noise source are identified through investigation of the acoustic pressure history induced by one blade, and it is confirmed that the dominant noise source is near the stabilizer. Since the acoustic pressure of the random pitch fan fluctuates according to blade passing, the dominant BPF noise for the uniform pitch fan is modified into some reduced discrete noises which have a 50Hz difference from BPF.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2002년도 유체기계 연구개발 발표회 논문집
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• pp.439-443
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• 2002

In this study, three-dimensional incompressible viscous flow analysis and optimization using response surface method are presented for the design of a jet fan. Steady, incompressible, three-dimensional Reynolds averaged Wavier-Stokes equations are used as governing equations, and standard k-$\epsilon$ turbulence model is chosen as a turbulence model. Governing equations are discretized using finite volume method. Sweep angles and maximum thickness of blade are used as design variables for the shape optimization of the impeller in response surface method. The experimental points which are needed to construct response surface are obtained from the D-optimal design and Full Factorial design and relations between design variables and response surface are examined.