• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.2192-2197
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• 2003

The purpose of this 3-D numerical simulation is evaluate the application of a commercial CFD code to predict 3-D flow and power characteristics of wind turbines. The experimental approach, which has been main method of investigation, appears to be its limits, the cost increasing with the size of the wind turbines, hence mostly limited to observing the phenomena on rotor blades. Therefore, the use of Computational Fluid Dynamics (CFD) techniques and Navier-Stokes solvers are considered a very serious contender. The flow solver CFX-TASCflow is employed in all computations in this paper. The 3-D flow separation and the wake distribution of 2 and 3 bladed Horizontal Axis Wind Turbines (HAWTs) are compared to Heuristic model and smoke-visualized experimental result by NREL(National Renewable Energy Laboratory). Simulated 3-D flow separation structure on the rotor blade is very similar to Heuristic model and the wake structure of the wind turbine is good consistent with smoke-visualized result. The calculated power of the 3 bladed rotor by CFD is compared with BEM results by TV-Delft. The CFD results of which is somewhat consist with BEM results, under an error less than 10%.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1806-1813
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• 2003

The stirred tank reactor is one of the most commonly used devices in industry for achieving mixing and reaction. Here we report on results obtained from the large eddy simulations of flow inside the tank performed using a spectral multi-domain technique. The computations were driven by specifying the impeller-induced flow at the blade tip radius. Stereoscopic PIV measurements (Hill et $al.^{(1)}$) along with the theoretical model of the impeller-induced flow (Yoon et $al.^{(2)}$) were used in defining the impeller-induced flow as superposition of circumferential, jet and tip vortex pair components. Large eddy simulation of flow in a stirred tank was carried out for the three different Reynolds numbers of 4000, 16000 and 64000. The effect of different Reynolds numbers is well observed in both instantaneous and time averaged flow fields. The instantaneous and mean vortex structures are identified by plotting an isosurfaces of swirling strength for all Reynolds numbers. The Reynolds number dependency of the nondimeansional eddy viscosity, resolve scale and subgrid scale dissipations is clearly shown in this study.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1453-1460
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• 2003

The present study investigates the effects of rib arrangements and aspect ratios of a rectangular duct simulating the cooling passage of a gas turbine blade. Two different V-shaped rib configurations are tested with the aspect ratios (W/H) of 3 to 6.82. One is the continuous V-shaped rib configuration with $60^{\circ}$ attack angle, and the other is the discrete V-shaped rib configuration with $45^{\circ}$ attack angle. The square ribs with the pitch to height ratio of 10.0 are installed on the test section in a parallel arrangement for both rib configurations. Reynolds numbers based on the hydraulic diameter are changed from 10,000 to 30,000. A naphthalene sublimation method is used to measure local heat/mass transfer coefficients. For the continuous V-shaped rib configuration, two pairs of counter-rotating vortices are generated in a duct, and high transfer region is formed at the center of the ribbed walls of the duct. However, for the discrete V-shaped rib configuration with $45^{\circ}$ attack angle, complex secondary flow patterns are generated in the duct due to its geometric feature, and more uniform heat/mass transfer distributions are obtained for all tested cases

• 한국정밀공학회지
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• 제27권8호
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• pp.48-53
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• 2010

5-axis CNC machining now is getting popular because it can deal with complex shapes such as impeller, turbine blade and propeller without additional equipment or process, proving a set of various tool orientations. CAM software related to 5-axis machining is being developed quickly so that users can take advantage of potential capacities of 5-axis machine tools. However, only a few researches can be found in the area of control strategy development for 5-axis machining. This paper proposes a 5-axis cross-coupling control system based on a novel tool orientation error model. The proposed tool orientation error model provides accurate information on the tool orientation error in real time, which in turn enables directly controlling the tool orientation accuracy. The proposed control system also employs a contour error model to calculate the contour error and reflect it in the control as well. The accuracy of the proposed tool orientation error model is verified and the performance of the 5-axis cross-coupling control system in terms of both contouring and tool orientation accuracy is evaluated through computer simulations compared with existing 5-axis control systems.

• 신재생에너지
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• 제3권3호
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• pp.63-71
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• 2007

본 연구의 목적은 3차원 풍력터빈 블레이드 최적형상설계를 위한 실용적이고 효율적인 설계과정을 구현하는 것이다. 국내 연안의 해상풍력에 적용하기 위해서 통계적 모델을 이용하여 풍황자료를 분석하였다. 설계에 관련된 많은 수의 설계변수를 효과적으로 관리하기 위해서 설계과정은 운용조건 최적화와 블레이드 형상설계의 2단계로 구성하였다. 실험계획법에 의해 추출된 각 운용조건 설계점은 형상설계를 위한 입력 값으로 제공된다. 형상설계 단계에서는 최소에너지손실 조건과 결합된 BEMT를 이용하여 각 블레이드 단면에서의 시위길이와 피치각 분포를 최적화하였다. 블레이드 단면 익형은 NREL S830을 이용하였고, 익형의 공력성능은 XFOIL을 이용하여 예측하였다. 설계된 블레이드 형상의 성능해석을 수행하고 그 결과를 바탕으로 반응면을 구성하였다. 좀 더 나은 성능을 가진 블레이드 형상을 찾기 위해서 초기설계공간에서 확률적 방법을 이용하여 타당성 있는 설계공간까지 운용조건 설계변수를 이동시키고 구배최적화 기법을 통해 각각의 제약함수를 만족하면서 연간에너지생산량을 최대로 하는 최적블레이드 형상을 구현하였다. 제시된 최적설계과정은 풍력터빈블레이드 개발에 실용적이고 신뢰성 있는 설계툴로서 사용이 가능하다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.104-111
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• 2011

To protect the turbine blade, many cooling techniques has developed. With all other things, film-cooling has been widely used as the important alternative. In the present work, numerical analysis has been performed to investigate and to compare the film-cooling performance of various film-cooling hole schemes such as cylindrical, crescent, louver, and dumbbell holes. To analyze the turbulent flow and the film-cooling mechanism, three-dimensional Reynolds-averaged Navier-Stokes analysis has been performed with shear stress transport turbulence model. The validation of numerical results has been assessed in comparison with experimental data. The characteristics of fluid flow and the film-cooling performance for each shaped hole have been investigated and evaluated in terms of centerline, laterally averaged and spatially averaged film-cooling effectivenesses. The dumbbell shaped hole shows better film-cooling effectiveness than other shaped holes. And the louver and cylindrical shaped hole shows lower one, and concentrated flow on centerline only.

• 대한기계학회논문집A
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• 제32권12호
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• pp.1088-1095
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• 2008

5-axis NC machining has a good advantage of the accessibility of tool motion by adding two rotary axes. It offers numerous advantages such as expanding machining fields in parts of turbo machineries like impeller, propeller, turbine blade and rotor, reasonable tool employment and great reduction of the set-up process. However, as adding two rotary axes, it is difficult to choose suitable machining conditions in terms of tool path, tool posture, feedrate control at a tool tip and post-processing. Therefore in this paper, it is proposed to decide suitable machining condition through an experimental method such as adopting various tool paths, tool postures, and feedrate types. Machining experiment on AL7075 for impeller is performed to define suitable machining condition, and measurement of surface roughness on machined surfaces depended on each machining condition is performed. By defining suitable machining condition, we should have conclusion as improving the surface quality in the aspect of surface roughness and machined shape of surface.

• Journal of Mechanical Science and Technology
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• 제18권3호
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• pp.407-418
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• 2004

Prandtl-Meyer expansion flow with homogeneous condensation is investigated experimentally and by numerical computations. The steady and unsteady periodic behaviors of the diabatic shock wave due to the latent heat released by condensation are considered with a view of technical application to the condensing flow through steam turbine blade passages. A passive control method using a porous wall and cavity underneath is applied to control the diabatic shock wave. Two-dimensional, compressible Navier-Stokes with the nucleation rate equation are numerically solved using a third-order TVD (Total Variation Diminishing) finite difference scheme. The computational results reproduce the measured static pressure distributions in passive and no passive Prandtl-Meyer expansion flows with condensation. From both the experimental and computational results, it is found that the magnitude of steady diabatic shock wave can be considerably reduced by the present passive control method. For no passive control, it is found that the diabatic shock wave due to the heat released by condensation oscillates periodically with a frequency of 2.40㎑. This unsteady periodic motion of the diabatic shock wave can be completely suppressed using the present passive control method.

• 대한기계학회논문집B
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• 제27권9호
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• pp.1290-1298
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• 2003

The stirred tank reactor is one of the most commonly used devices in industry for achieving mixing and reaction. Here we report on results obtained from the large eddy simulations of flow inside the tank performed using a spectral multi-domain technique. The computations were driven by specifying the impeller-induced flow at the blade tip radius. Stereoscopic PlY measurements (Hill et al. $^{(1)}$) along with the theoretical model of the impeller-induced flow (Yoon et al. $^{(2)}$) were used in defining the impeller-induced flow as superposition of circumferential, jet and tip vortex pair components. Large eddy simulation of flow in a stirred tank was carried out for the three different Reynolds numbers of 4000, 16000 and 64000. The effect of different Reynolds numbers is well observed in both instantaneous and time averaged flow fields. The instantaneous and mean vortex structures are identified by plotting an isosurfaces of swirling strength for all Reynolds numbers. The Reynolds number dependency of the non-dimensional eddy viscosity, resolved scale and subgrid scale dissipations is clearly shown in this study.

• 한국표면공학회지
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• 제37권4호
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• pp.226-233
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• 2004

The residual stresses on the surfaces of low carbon 12Cr steels used as a nuclear steam turbine blade material have been studied by controlling the flame hardening surface treatments. The temperature cycles on the surfaces of 12Cr steel were controlled precisely as a function of both the surface temperature and cooling rate. The final residual stress state generated by flame hardening was dominated by two opposite competitive contributions; one is tensile stress due to phase transformation and the other is compressive stress due to thermal contraction on cooling. The optimum processing temperatures required for the desirable residual stress and hardness were in the range of $850^{\circ}C$ to $960^{\circ}C$ on the basis of the specification of GE power engineering. It was also observed that the high residual tensile stress generated by flame hardening induced the cracks on the surfaces, especially across the prior austenite grain boundaries, and the material failure virtually, which might limit practical use of the surface engineered parts by flame hardening.