• 한국습지학회지
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• 제24권3호
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• pp.196-203
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• 2022

본 논문은 자유수면에서 마이크로 중력식 와류 수차의 성능에 블레이드 상대위치 변화의 영향을 이해하는 것이다. 일정한 와류 유동에서 자유수면 아래 상대 와류 수심비(y/h_v)의 범위 0 ~ 0.778 지점에 설치된 블레이드의 위치 변화에 따른 마이크로 와류 수차의 회전수, 전압 및 전류를 측정하였다. 유량은 0.0063 ~ 0.00662 m³/s 범위이다. 실험 결과는 유입되는 유속과 난류강도의 분포가 변하기 때문에 블레이드의 상대위치가 마이크로 와류 수차의 성능에 영향을 미치는 것으로 나타났다. 와류 수차에서 발생하는 에너지의 최대량은 상대 와류 수심비 0.111 ~ 0.222 지점에서 발생했다. 상대 와류 수심비 0.111 지점의 출력은 자유수면 아래 상대 와류 수심비 0.588 지점보다 약 2.4배 더 크게 나타난다.

• 대한기계학회논문집B
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• 제31권8호
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• pp.688-693
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• 2007

To improve aerodynamic efficiency of the Smart Un-manned Aerial Vehicle(SUAV), vortex generator was applied along the wing upper surface during SUAV tests. Vortex generator, initially used in TR-S2 configuration to enhance lift characteristic, increased lift coefficient. Meanwhile vortex generator produced excessive drag and eventually reduced lift-to-drag ratio. To examine the effect of vortex generator's height, three different heights of vortex generator were used for various SUAV configuration. Vortex generator of 3mm height used in TR-S4 configuration produced 3.1% increase in maximum lift coefficient and 1.5% reduction in lift-to-drag ratio.

• 대한기계학회논문집B
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• 제26권1호
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• pp.82-93
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• 2002

The effects of the interaction between the flow and temperature field and a boundary layer due to a variety of the height of a vortex generator are experimentally investigated. The test facility consists of a boundary-layer wind tunnel with the vortex generator protruding from the bottom surface. In order to control the strength of the longitudinal vortices, the angle of attack and the spacing distance of the vortex generator are 20 degree and 40 mm, respectively. The height of the vortex generator (H) is 15 mm, 20 mm and 30 mm and the cord length of it is 50 mm. Three-component mean velocity measurements are made using a 5-hole probe system and the surface temperature distribution is measured by the hue capturing method using thermochromatic liquid crystals. By using the method mentioned above, the following conclusions are obtained from the present experiment. The boundary layer is thinned in the downwash region where the strong downflow and the lateral outflow of the boundary layer fluid occur and thickened in the upwash re,3ion where the longitudinal vortex sweeps low momentum fluid away from the bottom surface. In case that the height of the vortex generator increases, the averaged circulation and the maximum vorticity of the vortex pair decrease. The contours of the non-dimensional temperature show the similar trends fur all the cases (H=15 mm, 20 mm and 30 mm). The peak augmentation of the distribution of the local non-dimensional temperature occurs in the downwash region near the point of minimum boundary-layer thickness.

• Journal of Mechanical Science and Technology
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• 제17권6호
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• pp.925-934
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• 2003

An experimental study is performed to investigate the characteristics of near wake flow behind a circular cylinder with serrated fins using a constant temperature anemometer and flow visualization. Various vortex shedding modes are observed. Fin height and pitch are closely related to the vortex shedding frequency after a certain transient Reynolds number. The through velocity across the fins decreases with increasing fin height and decreasing fin pitch. Vortex shedding is affected strongly by the velocity distribution just on top of the finned tube. The weaker gradient of velocity distribution is shown as increasing the freestream velocity and the fin height, while decreasing the fin pitch. The weaker velocity gradient delays the entrainment flow and weakens its strength. As a result of this phenomenon, vortex shedding is decreased. The effective diameter is defined as a virtual circular cylinder diameter taking into account the volume of fins, while the hydraulic diameter is proposed to cover the effect of friction by the fin surfaces. The Strouhal number based upon the effective diameters seems to correlate well with that of a circular cylinder without fins. After a certain transient Reynolds number, the trend of the Strouhal number can be estimated by checking the ratio of effective diameter to inner diameter. The normalized velocity and turbulent intensity distributions with the hydraulic diameter exhibit the best correlation with the circular cylinder's data.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.160-167
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• 2008

The effects of squealer rim height on three-dimensional flows and aerodynamic losses downstream of a high-turning turbine rotor blade have been investigated for a typical tip gap-to-chord ratio of h/c=2.0%. The squealer rim height-to-chord ratio is changed to be $h_{st}/c$=0.00(plane tip), 1.37, 2.75, 5.51, and 8.26%. Results show that as $h_{st}/c$ increases, the tip leakage vortex tends to be weakened and the interaction between the tip leakage vortex and the passage vortex becomes less severe. The squealer rim height plays an important role in the reduction of aerodynamic loss when $h_{st}/c{\leq}2.75%$. In the case of $h_{st}/c{\geq}5.51%$, higher squealer rim cannot provide an effective reduction in aerodynamic loss. The aerodynamic loss reduction by increasing $h_{st}/c$ is limited only to the near-tip region within a quarter of the span from the casing wall.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2002년도 추계학술대회 논문집
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• pp.27-30
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• 2002

An experimental study is performed to investigate the characteristics of near wake behind a circular cylinder with serrated fins using the constant temperature anemometer and through flow visualization. Previous report(Boo at al., 2001) shows that there are three different modes in vortex shedding behavior. This paper is focused on the identification of the physical reasons why the difference is occured in vortex shedding. The through flow velocity crossing fins decreases as increasing fin height and decreasing fin pitch mainly due to the flow resistence. Vortex shedding is affected strongly by velocity distribution around fin tube, especially by the velocity gradient. The velocity distribution at X/d=0.0 has lower gradient with increasing freestream velocity and fin height and decreasing fin pitch. Those differences in velocity gradients generate different vortex shedding mechanism.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.494-499
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• 2011

One of the devices to prevent separated flow over a wing or a flap at high angle of attack is a vortex generator. In the present work, we numerically study the flow around a low-profile or micro vortex generator whose height is less than local boundary layer thickness which can delay separation with a minimum drag penalty owing to its very small wetted surface area. As a first step toward a parametric study to efficiently design this MVG flow control system, we simulate the flow around a single MVG on a flat plate. For the simulation, we employ OpenFOAM with Launder-Sharma ${\kappa}$-epsilon model. The analysis results are validated by comparing with experimental results of a rectangular MVG at an angle of attack of 10 degrees whose height is 20% of local boundary layer. Important results and aspects of this numerical study are discussed. We also simulate the flow around rectangular, triangular and trapezoidal MVGs and the results are compared

• 한국습지학회지
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• 제22권2호
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• pp.121-129
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• 2020

본 논문은 자유수면을 가지는 와류유동 내 저낙차에서 마이크로 소수력에 관한 실험 연구이다. 내부 곡선 모서리가 있는 직선, 곡선, 비틀린 블레이드의 와류 높이, 터빈 회전 및 토크를 개수로 유입구의 유량 0.0069 ㎥/s 조건에서 측정하였다. 실험결과로서 최적의 와류 강도는 와류 발생부의 외부직경과 유출구 직경 비율 0.17~18.5 범위에서 발생했다. 직선 블레이드 출력과 효율은 다른 블레이드와 비교하여 높게 나타났다. 가장 높게 생성된 에너지는 12.33 W이고, 토크는 0.91 N·m이다. 유효낙차를 고려한 경우 가장 높은 효율은 29.5 %인 반면 와류 높이를 고려한 가장 높은 효율은 회전수 132 rpm에서 80.5 %이다. 직선 블레이드의 와류 유속은 개수로 유입구의 평균 유속보다 약 2.8배 더 크게 나타난다.

• 한국분무공학회지
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• 제28권3호
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• pp.126-133
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• 2023

This study analyzes the flow characteristics and sponge ball recovery performance in a ball strainer according to vortex promoter design variables through flow-particle analysis based on actual experiments to derive a method for improving the recovery rate of cleaning sponge balls of CTCS applied to existing power plants. Based on the ball strainer in CTCS used in the power plant, the experiment was conducted by changing the design factor of the improved shape. In addition, flow and particle analysis were performed under the same conditions as the experiment to numerically the flow characteristics and recovery rate in the ball strainer according to the design factor of the vortex promoter. As a result of the study, it was confirmed that the recovery performance was improved by about 3% by changing the design height of the Vortex promoter. And when comparing the difference between maximum and minimum recovery rate, it was found that the effect on the recovery performance increased slightly according to the distance condition compared to the vortex promoter design height condition.

• 한국환경기술학회지
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• 제19권6호
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• pp.528-535
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• 2018

본 연구에서는 전산유체역학(CFD) 모델을 이용하여, 건물 외관비에 따른 건물협곡에서의 소용돌이 현상을 재현하고 정량적인 해석을 시도하였다. 이를 위하여 건물협곡의 폭(W)을 기준으로 건물의 길이(L) 및 높이(H) 증가에 따른 민감도 실험을 수행하였으며, 건물협곡에서의 바람 벡터장과 2차 역회전 소용돌이의 형성 등을 분석하였다. 수평소용돌이의 경우에는 건물의 길이 증가에 따라 성장하다가 L/W=2.5부터 건물협곡의 중앙부에서 벡터의 크기 약화 및 방향 변화 등의 조짐이 보이기 시작하였고, L/W=3.0 이상에서 흐름이 분리되어 1차 소용돌이는 약화되고 건물협곡의 안쪽에서 2차 역회전 소용돌이가 형성되었다. 연직소용돌이의 경우에는 건물의 높이 증가에 따라 성장하다가 H/W=2.5부터 건물협곡의 하부에서 벡터의 방향전환 현상이 나타나기 시작하였고, H/W=3.5 이상의 조건에서 1차 소용돌이는 약화되고 2차 역회전 소용돌이가 형성되었다.