• 대한기계학회논문집B
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• 제26권12호
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• pp.1738-1746
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• 2002

In the FSI (Fluid-Structure Interaction) problems, two different governing equations are to be solved together. One is fur the fluid and the other for the structure. Furthermore, a kinematic constraint should be imposed along the boundary between the fluid and the structure. We use the combined formulation, which incorporates both the fluid and structure equations of motion into a single coupled variational equation so that it is not necessary to calculate the fluid force on the surface of structure explicitly when solving the equations of motion of the structure. A two-dimensional channel flow divided by a Bernoulli-Euler beam is considered and the dynamic response of the beam under the influence of channel flow is studied. The Navier-Stokes equations are solved using a P2P1 Galerkin finite element method with ALE (Arbitrary Lagrangian-Eulerian) algorithm. The internal structural damping effect is not considered in this study and numerical results are compared with a previous work fer steady case. In addition to the Reynolds number, two non-dimensional parameters, which govern this fluid-structure system, are proposed. It is found that the larger the dynamic viscosity and density of the fluid are, the larger the damping of the beam is. Also, the added mass is found to be linearly proportional to the density of the fluid.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2009년도 추계학술대회 논문집
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• pp.465-465
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• 2009

Wind power is one of the most reliable renewable energy sources and the installed wind turbine capacities are increasing radically every year. Although wind power has been favored by the public in general, the problem with the impact of wind turbine noise on people living in the vicinity of the turbines has been increased. Low noise wind turbine design is becoming more important as noise is spreading more adverse effect of wind turbine to public. This paper demonstrates the design of 10 kW class wind turbines, each of three blades, a rotor diameter 6.4m, a rated rotating speed 200 rpm and a rated wind speed 10 m/s. The optimized airfoil is dedicated for the 75% spanwise position because the dominant source of a wind turbine blade has been known as trailing edge noise from the outer 25% of the blade. Numerical computations are performed for incompressible flow and for Mach number at 0.145 and for Reynolds numbers at $1.02{\times}10^6$ with a lift performance, which is resistant to surface contamination and turbulence intensity. The objective in the low design process is to reduce noise emission, while sustaining high aerodynamic efficiency. Dominant broadband noise sources are predicted by semi-empirical formulas composed of the groundwork by Brooks et al. and Lowson associated with typical wind turbine operation conditions. During the airfoil redesign process, the aerodynamic performance is analyzed to minimize the wind turbine power loss. The results obtained from the design process show that the design method is capable of designing airfoils with reduced noise using a commercial 10 kW class wind turbine blade airfoil as a basis. The new optimized airfoil clearly indicates reduction of total SPL about 3 dB and higher aerodynamic performance.

• 대한기계학회논문집
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• 제10권6호
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• pp.852-860
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• 1986

본 연구에서는 청정실 내부에 하나의 작업대가 유동을 방해하고 있으며, 출구 공기덕트가 2개이기 때문에 출구의 평균압력조건은 주어지나 출구속도의 경계조건이 간단히 기술되지 않는 청정실내에서 유동을 예측하고자 하였으며, 수치계산상의 구체 적인 방법을 논하였다. 그 결과로서 작업대 위치 및 각 출구에서의 압력조건에 따른 유동장의 형태 및 각 출구에서의 유출유량 비율등을 논하였다.

• 대한기계학회논문집
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• 제13권1호
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• pp.178-189
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• 1989

본 연구에서는 우선 승용차의 1/10 모형의 형상을 더욱 단순화시킨 2차원 자동차형 물체를 대상으로 하여 그 주위의 압력, 속도 및 난류량의 분포를 측정하고, 또한 울터프트(wool tuft)를 이용한 유동가시화법으로 후류구조를 파악함으로써 향후 계속될 실험적 및 수치해석적 연구의 기초를 마련하고자 한다.

• 대한기계학회논문집B
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• 제25권9호
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• pp.1253-1262
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• 2001

Experimental study is conducted to investigate the heat/mass transfer and flow characteristics for the flow over backward-facing step and cavities. A naphthalene sublimation method has been employed to measure the mass transfer coefficients on the duct wall and LDV system has been used to obtain mean velocity profiles and turbulence intensities. Reynolds number based on the step height and free stream velocity is 20,000 and St numbers of acoustic excitations given to separated flow are 0.2 to 0.4. The spectra of streamwise velocity fluctuation show a sharp peak forcing frequency for an acoustically excited flow. The results reveal that the vortex pairing and overall turbulence level are enhanced by the acoustic excitation and a significant decrease in the reattachment length and the increased turbulence intensity are observed with the excitation. A certain acoustic excitation increases considerably the heat/mass transfer coefficient at the reattachment point and in the recirculation region. For the cavities, heat/mass transfer is enhanced by the acoustic excitation due to the elevated turbulence intensity. For the 10H cavity, the flow pattern is significantly changed with the acoustic excitation. However, for the 5H cavity, the acoustic excitation has little effect on the flow pattern in the cavity.

• 대한기계학회논문집B
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• 제25권12호
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• pp.1821-1830
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• 2001

The flow around free end of a finite circular cylinder (FC) embedded in an atmospheric boundary layer has been investigated experimentally. The experiments were carried out in a closed-return type subsonic wind tunnel with varying aspect ratio of the finite cylinder mounted vertically on a flat plate. The wakes behind a 2-D cylinder and a finite cylinder located in a uniform flow were measured for comparison. Reynolds number based on the cylinder diameter was about Re=20,000. A hot-wire anemometer was employed to measure the wake velocity and the mean pressure distributions on the cylinder surface were also measured. The flow past the FC free end shows a complicated three-dimensional wake structure and flow phenomenon is quite different from that of 2-D cylinder. The three-dimensional flow structure was attributed to the downwashing counter rotating vortices separated from the FC free end. As the FC aspect ratio decreases, the vortex shedding frequency decreases and the vortex formation length increases compared to that of 2-D cylinder. Due to the descending counter-rotating twin-vortex, near the FC free end, regular vortex shedding from the cylinder is suppressed and the vortex formation region is hardly distinguished. Around the center of the wake, the mean velocity for the FC located in atmospheric boundary layer has large velocity deficit compared to that of uniform flow.

• 한국가시화정보학회지
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• 제16권1호
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• pp.30-36
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• 2018

In the present study, we investigate the flow characteristics of a quadrotor UAV in a hovering mode by measuring multiple two-dimensional velocity fields in the wake. The experiment is conducted at Re = 24,000 in a chamber large enough to neglect the ground effect, where Re is the Reynolds number based on the rotor chord length and the rotor tip speed. The rotational speed of the rotor is determined by an optical tachometer so that the lift force can be balanced with the weight of the UAV. The velocity field measured on the center plane of the rotor shows that the vortices are shedding from the tip of the rotor, inducing large fluctuations in the streamwise velocity along the wake shear layer. The strength of the rotor-tip vortex shedding is asymmetric with respect to the rotor axis due to the interaction between the rotor and the wake centerline of each rotor is inclined to the center of the UAV due to the pressure difference caused by the induced velocity. The wake from each rotor moves closer to each other while traveling in the streamwise direction, and then is merged together inducing large fluctuations in the transverse velocity. Due to the wake merging, on the center plane of the UAV, the velocity increases in the streamwise direction showing two-peak structure in the streamwise velocity contours.

• 한국항공우주학회지
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• 제30권1호
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• pp.1-8
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• 2002

자유류 속도가 40 m/sec 이고 날개의 뿌리시위에 기준한 레이놀즈수가 1.76${\times}$10$^6$인 상태에서 옆미끄럼이 삼각 날개 와류에 미치는 영향을 실험적으로 연구하였다. 받음각 범위는 16$^{\circ}$에서부터 28$^{\circ}$까지 이었으며 옆미끄럼각은 0$^{\circ}$, -10$^{\circ}$, 그리고 -20$^{\circ}$이었다. 옆미끄럼각은 바람쪽과 바람 반대쪽 와류 모두의 강도를 감소시키고, 바람쪽 와류의 붕괴를 촉진시킴이 관찰되었다. 옆미끄럼각 -10$^{\circ}$에서 바람 반대쪽의 와류는 받음각이 증가함에 따라 그 강도가 증가하였다. 이와 같은 옆미끄럼 조건에서 날개 와류의 비대칭적인 발달과 붕괴는 삼각 날개의 롤링모멘트를 어느 특정한 높은 받음각에서 급격히 바뀌게 할 수 있으며, 이는 일종의 롤링 모멘트 불안정성으로 간주할 수 있다.

• 에너지공학
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• 제29권1호
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• pp.34-43
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• 2020

풍력발전기 로터의 저속운전 가능성에 대해 기동토크를 평가하고자 하였다. 본 연구에서 살펴본 저속시동 가능성의 날개는 초임계에어포일을 보완하여 AMI계열(AMI903 및 AMI904)의 날개를 제안하여 공력성능을 유지하며 제작상 및 유지보수의 어려움을 제거하였다. 따라서 본 연구는 FLUENT를 이용하여 난류유동 해석을 통해 제안된 날개의 받음각(-180°~+180°)에 대한 항력계수와 양력계수를 제시하였으며, 이 값들로부터 정지하고 있는 날개의 회전 위치에 따른 접선방향의 토크계수를 정의하여 제시하였다. 기동력의 크기와 방향을 결정할 토크계수는 대부분 양의 값(반시계방향)으로 나타났으며 특별히 받음각이 0°에서 180° 및 -90°에서 -180°에서 양의 값이며 0°에서 -90°에서 매우 작거나 음의 값을 나타냈다. 한편 기동토크는 두께가 얇은 AMI903보다 두꺼운 AMI904에서 더 큰 것으로 나타났다.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
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• pp.289-296
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• 2004

The present study has been performed to investigate the influences of rectangular fins on heat transfer in an impingement/effusion cooling system with crossflow. To simulate the impingement/effusion cooling system with initial crossflow, two perforated plates are placed in parallel and staggered arrangements with a gap distance of 2 times of the hole diameter. The crossflow passes between the plates, and various rectangular fins are installed on the plates. Reynolds number based on the hole diameter is fixed to 10,000 and the flow rate of crossflow is changed from 0.5 to 1.5 times of that of the impinging jet. A naphthalene sublimation method is used to obtain the heat/mass transfer coefficients on the effusion plate. Also to analyze the flow characteristics, a numerical calculation is performed. When rectangular fins are installed, the flow and heat transfer pattern is changed greatly from case without fins. In the injection hole region, the jet impinges on effusion plate without deflection and wall jet spreads symmetrically. In the effusion region, the crossflow accelerates due to the decrease of cross-sectional area in the channel. Local heat/mass transfer coefficients are enhanced significantly compared to case without fins. As the blowing ratio increases, the effect of fins against the crossflow becomes more significant and then the higher average heat/mass transfer coefficients are obtained than the case without fins.