• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2000년도 유체기계 연구개발 발표회 논문집
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• pp.236-244
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• 2000

As the second part of the author's study, the aerodynamic blockage and the slip factor of 8 centrifugal compressor impellers are investigated, when the flow rate is changed from numerical stall to choke, using three-dimensional Navier-Stokes analysis results. Based on all the exit blockage distributions, an improved model equation with two adjusting coefficients is developed for the use in design processes with the agile engineering purpose. A popular expression of constant slip factors, the Wiesner's equation, cannot be applied in design processes when more accurate prediction is strongly required at design and off-design points. Slip factor variation is found to be also influenced by the blade loadings at midspan. When the flow rate is changed, a pattern of the slip factor variations is assumed to be a simple form which can be explained using midspan blade loading distributions.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2010년도 춘계학술대회 논문집
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• pp.72-73
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• 2010

In this paper, the main noise sources and its radiated noise levels of upwind horizontal-axis wind turbines are experimentally and theoretically investigated. Theoretical predictions for indentifying the dominant source locations are made by using the empirical noise prediction model of Brooks et al. (1989) for the airfoil self noise. Through the comparison of theoretical results with the experimental results, turbulence-boundary-layer-trailing-edge (TBL-TE) noise is revealed to be the dominant source over all frequency range and separation and stall (S-S) noise is possibly important in the relative lower frequency range compared with TBL-TE noise.

• 대한기계학회논문집B
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• 제32권7호
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• pp.549-557
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• 2008

Despite of the laminar-turbulent transition region co-exist with fully turbulence region around the leading edge of an airfoil, still lots of researchers apply to fully turbulence models to predict aerodynamic characteristics. It is well known that fully turbulent model such as standard k-model couldn't predict the complex stall and the separation behavior on an airfoil accurately, it usually leads to over prediction of the aerodynamic characteristics such as lift and drag forces. So, we apply correlation based transition model to predict aerodynamic performance of the NREL (National Renewable Energy Laboratory) Phase IV wind turbine. And also, compare the computed results from transition model with experimental measurement and fully turbulence results. Results are presented for a range of wind speed, for a NREL Phase IV wind turbine rotor. Low speed shaft torque, power, root bending moment, aerodynamic coefficients of 2D airfoil and several flow field figures results included in this study. As a result, the low speed shaft torque predicted by transitional turbulence model is very good agree with the experimental measurement in whole operating conditions but fully turbulent model(${\kappa}-\;{\varepsilon}$) over predict the shaft torque after 7m/s. Root bending moment is also good agreement between the prediction and experiments for most of the operating conditions, especially with the transition model.

• 한국항공우주학회지
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• 제35권2호
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• pp.124-129
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• 2007

동 연구에서는 전진비행하는 로터의 평균 유입류 예측기법 중 Drees 선형모델, 몇가지 변형된 형태의 Mangler & Squire 모델을 서로 비교하여 각 유입류 모델의 특성을 알아내고, KARI 자체 자유후류기법 코드의 해석결과를 함께 비교하여 각 유입류 예측기법의 특성을 파악하였다. 각 예측기법의 비교를 위해 유입류 실험치가 존재하는 로터에 대하여 전진비 0.15, 0.23 및 0.30의 3가지 비행조건을 적용하여 예측한 결과를 비교 분석하였다. Drees 모델의 경우 비교적 실험치에 근접하게 예측하나, 선형모델의 한계로 인해 유입류의 비균일성을 모델링하기에는 미흡하며, Mangler & Squire 모델은 끝단을 제외하고는 비교적 실험치에 근접하게 예측함을 알 수 있었으며, KARI의 자유후류기법은 유입류의 비균일성을 매우 잘 예측하나, 동체에 의한 올려흐름 효과, 후퇴부에서의 동적실속 효과 등의 추가 고려가 필요함을 알 수 있었다.

• 한국유체기계학회 논문집
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• 제11권5호
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• pp.15-21
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• 2008

In modem wind power system of large capacity above 1MW, horizontal axis wind turbine(HAWT) is a common type. And, the optimum design of wind turbine to guarantee excellent power performance and its reliability in structure and longevity is a key technology in wind Industry. In this study, mathematical expressions based upon the conventional BEMT(blade element momentum theory) applying to basic 1MW wind turbine blade configuration design. Power coefficient and related flow parameters, such as Prandtl's tip loss coefficient, tangential and axial flow induction factors of the wind turbine analyzed systematically. X-FOIL was used to acquire lift and drag coefficients of the 2-D airfoils and we use Viterna-Corrigan formula to interpolate the aerodynamic characteristics in post-stall region. In order to predict the performance characteristics of the blade, a performance analysis carried out by BEMT method. As a results, axial and tangential flow factors, angle of attack, power coefficient investigated in this study.

• International Journal of Fluid Machinery and Systems
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• 제6권2호
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• pp.94-104
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• 2013

This paper describes the design to increase the blade loading factor of a low speed axial flow fan from normal 0.42 to highly loaded 0.55. A three-dimensional viscous solver is used to model the flows in the highly-loaded and normal loaded stages over its operation range. At the design point operation the static pressure rise can be increased by 20 percent with a deficit of efficiency by 0.3 percent. In the highly loaded fan stage, the rotor hub flow stalls, and separation vortex extends over the rotor hub region. The backflow, which occurs along the stator hub-suction surface, changes the exit flow from the prescribed axial direction. Results in this paper confirm that the limitation of the two dimensional diffusion does not affect primarily on the fan's performance. Highly loaded fan may have actually better performance than its two dimensional design. Three dimensional designing approaches may lead to better highly loaded fan with controlled rotor hub stall.

• Asian-Australasian Journal of Animal Sciences
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• 제8권1호
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• pp.59-66
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• 1995

Energy obtained by grazing cattle in oil palm plantations is usually used for maintenance of body functions, the construction of body tissues and pregnancy, the synthesis of milk and the conversion to mechanical energy used for activities such as walking, eating and others. In this study, attempt was made to estimate metabolizable energy (ME) requirement of grazing cattle. Models of ME requirement (MER) for maintenance, gain, pregnancy, lactation and activities were developed. ME system and units were used because of wide recognition. Estimation of ME intake in grazing cattle was expressed as MEVI = $14.58{\times}VI{\times}DMD$, and under grazing condition MEVI = $MER_i$. MER was expressed as a function of net energy(NER, MJ) required for the i'th body function. Coefficient of efficiency for conversion of ME into net energy(ki) was adopted from literatures. Quantifying of ME requirement for Kedah-Kelantan cattle under grazing condition was made by using equation MERM = NEM / kn. The estimated values of MER for Kedah-Kelantan cattle is quite reasonable if compared with other estimates as reported in literatures from stall-fed animals. Dynamic MER models for grazing herd was developed in order to estimate ME requirement for maintenance and productions. These ME requirement models can be used for prediction of energy utilization pattern of the herd in the grazing systems.

• 한국전산유체공학회지
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• 제21권3호
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• pp.48-54
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• 2016

In the present work, numerical simulations were conducted on the scaled model of the BWB type UCAV in the subsonic region using ANSYS FLUENT V15. The prediction method was validated through comparison with experimental results and the effect of the twisted wing was investigated. To consider the transitional flow phenomenon, ${\gamma}$ transition model based on SST model was adopted. The coefficients of lift, drag and pitching moment were compared with experimental results and the pressure distribution and streamlines were investigated. The twisted wing decreases the lift force but increases lift-to-drag ratio through delay of stall and leading edge vortex's movement to the front, also the non-linearity of the pitching moment is decreased.

• 한국전산유체공학회지
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• 제18권3호
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• pp.51-59
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• 2013

A significant change in aerodynamic characteristics of wind turbine blade can occur by ice formed on the surface of the blade operated in cold climate. The ice accretion can result in performance loss, overloading due to delayed stall, and excessive vibration associated with mass imbalance. In this study, the impact of ice accretion on the aerodynamic characteristics of NREL 5MW wind turbine blade sections is examined by a CFD-based method. It is shown that the thickness of ice accretion increases from the root to the tip and the effects of icing conditions such as relative wind velocity play a significant role in the shape of ice accretion. In addition, the computational results are used to assess the degradation in the lift and drag coefficients of the blade sections.

• 한국전산유체공학회지
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• 제18권1호
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• pp.91-97
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• 2013

In the present study, the effects of contaminant accumulation and surface roughness on the aerodynamic performance of wind turbine blade sections were numerically investigated by using a flow solver based on unstructured meshes. The turbulent flow over the rough surface was modeled by a modified ${\kappa}-{\omega}$ SST turbulence model. The calculations were made for the NREL S809 airfoil with varying contaminant sizes and positions at several angles of attack. It was found that as the contaminant size increases, the degradation of the airfoil performance becomes more significant, and this trend is further amplified near the stall condition. When the contaminant is located at the upper surface near the leading edge, the loss in the aerodynamic performance of the blade section becomes more critical. It was also found that the surface roughness leads to a significant reduction of lift, in addition to increased drag.