• Journal of Wetlands Research
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• v.22 no.2
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• pp.121-129
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• 2020

This paper described a laboratory investigation of micro hydropower at lower head water in a free vortex flow. The vortex height, turbine rotation and torque for straight blade with inner curved edge, twisted blade and curved blade were investigated at the flow rate of 0.0069 ㎥/s in the inlet channel. The results showed that the optimum vortex strength occurred within the range of the diameter of basin to the outlet diameter ratios of 0.17~18.5. The power output and efficiency of straight blade were higher as compared to other blades. The highest amount of generated energy was 12.33 W, the torque was 0.91 N·m and the highest efficiency by considering effective head was 29.5 %, whereas the highest efficiency by considering vortex height was 80.5 % at the rotational speed of 132 rpm. The water vortex velocity of straight blade was about 2.8 times larger than the mean velocity in the inlet channel.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.1
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• pp.28-35
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• 2002

In cavity flow, the rectangular step generates so strong sound that many researchers have investigated method to suppress the nois during interaction between vortical flow and rectangular forward step. In this study the flow noise from the vortex motion in two-dimentional low Mach number flow past a forward step with various chamfering angle is calculated numerically. Inviscid incompressible discrete vortex model and matched asymptotic expansion(MAE) theory are applied to obtain the inner flow field and the outer noise field. Both source acoustic pressure and sound intensity are obtained with various chamfering height, chamfering angle and initial vortex position. The pressure amplitude is most suppressed when the chamfering angle is between $15^{\circ}C$ and $30^{\circC}$ at the chamfering length of 30% of the step height.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1997.11a
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• pp.8-9
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• 1997

산업의 발달과 환경에 대한 관심이 높아짐에 따라 고효율, 저공해인 가스터빈의 응용범위가 넓어지고 있는 추세이다. 가스터빈 기관의 효율을 높이기 위해서는 터빈 입구온도를 높이는 것이 필수적인데 이는 재질에 의해 제한 받게 되고 이 때문에 효과적인 냉각방법의 필요성이 대두되었다 충돌제트는 국소적으로 높은 열/물질 전달 효과를 얻을 수 있어서 터빈 블레이드 냉각과 연소기 벽면 냉각에 효과적으로 응용 될 수 있다. 이러한 충돌제트의 냉각효과는 제트출구의 초기조건에 매우 민감한데 Kelvin-Helmholts 불안정은 불안정한 자유전단층에서 자연적인 와류생성(roll up)과 개개의 와류고리 형성의 원인이 되고 이 고리의 성장과 병합(pairing)은 제트의 유동특성에 상당히 영향을 미친다. 제트주위에 생성되는 이러한 와류에 의해 제트중심에서 속도와 난류강도가 변하게 된다. 이러한 제트초기의 불안정성은 하류에서의 와류성장에 영향을 끼치기 때문에 와류의 조절에 의한 충돌 면에의 열 전달 효과 상승을 기대할 수 있다. 이 조절방법은 크게 두 가지로 나눌 수 있는데 하나는 제트주의 환형관에 이차유동을 가하여 와류를 직접 제어함으로써 자유전단류(free shear layer flow)의 안정성 원리를 이용하여 열 전달을 촉진하는 것이고 다른 하나는 음향여기(acoustic exitation)를 사용하여 제트주위의 와류형성을 조절하는 것인데, 자연적으로 형성되는 와류의 주파수(와류의 고유주파수)나 부조화 주파수(subharmonic)로 음향여기 시키는 경우 제트 주위 와류는 더욱 증폭되고 그렇지 않은 경우 제트주위 와류의 형성이 억제되어 더 긴 제트코어의 길이 및 제트코어 주위에서 작은 크기의 와류들이 형성된다.

• Journal of the Korean Society of Marine Environment & Safety
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• v.30 no.2
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• pp.252-261
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• 2024

This research establishes design standards for vortex reduction devices (VRDs) aimed at minimizing underwater radiated noise by mitigating horseshoe vortex (HSV) and root vortex (RV) generated at the junction of appendages and the hull of underwater vehicles. Initial analysis replaced the influence of appendage dimensions and flow velocity with the Reynolds number by verifying the Reynolds similarity of vortex flows. The three-dimensional surfaces of VRDs were parameterized using Bezier curves. Optimal length-to-height ratios were identified by evaluating the vortex reduction performances of VRDs with various dimensions. Ultimately, non-dimensional design standards were derived for VRDs, ensuring effective vortex reduction across any appendage, thereby enhancing stealth performance.

• Journal of Energy Engineering
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• v.14 no.4 s.44
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• pp.241-247
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• 2005

Heat transfer enhancement and pressure loss penalty caused by three-row winglets built in three-row tube-bundles in an in-line arrangement, are compared between 'common flow up' and 'common flow down' winglet configurations. The 'common flow down' winglet-pairs recommended by the previous researchers bring about $10\%$ to $25\%$ increase in heat transfer enhancement and $20\%$ to $35\%$ increase in pressure loss penalty, in comparison with fin-tube bundles without winglets. For the 'common flow up' winglet-pairs, the spanwise distance between the trailing edges (${\Delta}y$) of winglet pairs was changed and investigated. Two types ot winglet are applied for triangular and rectangular shapes. In the triangular winglets with ${\Delta}y$=5 mm in in-line tube bundles, the heat transfer increased up to $10\%$, and simultaneously the pressure loss decreased by $8\%$ to $15\%$ for the Reynolds number (based on two times channel height) ranging from 300 to 2700, when the 'common flow up' winglets were built in. The performance of fin-tube bundles with triangular winglets is much superior to the rectangular one, because of the smaller pressure-loss penalty.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1997.04a
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• pp.63-72
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• 1997

본 논문은 분사제트 주위에 형성되는 와류를 조절하여 제트를 제어하기 위하여 유동가시화, 속도분포 및 난류성분을 측정하는 실험을 수행하였다. 와류를 조절하기 위한 방법으로 제트노즐 주위에 환형관을 설치하여 환형관으로부터 2차제트를 분사 또는 흡입함으로써 제트주위에 형성되는 전단류를 변화시켰다. 2차제트 분사시 주제트 주위에 형성되는 와류의 발달을 억제함으로써 제트 포텐셜코어의 길이가 아주 길어지는 제트유동을 얻을 수 있었다. 환형관으로부터 주제트주위의 유체를 흡입하는 경우 제트주위의 전단류가 흡입비 R=1.3∼l.65에서 대류불안정성에서 절대불안정성으로 바뀜으로써 형성된 와류가 하류에서 제트중심부까지 발전, 결합되는 것을 방지하여 더 긴포텐셜코어와 중심에서 낮은 난류강도를 얻었다. 위의 결과는 환형관 주위에 부착한 깃의 높이 변화에 따라서 변화하였는데, 이것은 깃이 환형관을 통한 흡입유동의 유로역할을 함으로써 제트밖으로부터 흡입되는 것을 방지할 수 있었다. 분사제트 벡터링을 위하여 제트노즐 주위의 환형관을 이등분하여 한쪽으로만 제트주위의 유동을 흡입함으로써 제트주위에 다른 전단류를 형성함과 동시에 Coanda효과를 이용하여 분사제트를 편향시켰다. 편향되는 정도 및 난류성분은 홉입속도 비에 따라서 크게 바뀌었다.

• Journal of Wetlands Research
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• v.23 no.3
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• pp.234-241
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• 2021

This paper contributes to the understanding of the effect of pulley on the performance of the vortex turbine in free water surface. The experimental work was to analyze the rotation, voltage and current of the turbine due to physical factors (vortex height, velocity, effective head, etc.) at flow rates ranging from 0.0069 to 0.0077 m³/s in the inlet channel. As a result, the experimental values showed that voltage, current and rotational speed of the vortex turbine decreased with increasing the pulley ratio regardless of the blade type. The efficiency of straight blade and twisted blade was 52 % at the gear ratio of 0.45, whereas the efficiency of small twisted blade was 54 % at the pulley ratio of 0.21. The highest amount of the energy generated by the water free vortex turbine occurred within a pulley ratio of 0.5. The efficiency of this vortex turbine was observed at 0.2 ~ 58 % depending on the pulley ratio.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.4
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• pp.336-343
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• 2009

Secondary flow losses can be as high as 30~50% of the total aerodynamic losses generated in the cascade of a turbine. Therefore, these are important part for improving a turbine efficiency. As well, many studies have been performed to decrease the secondary flow losses. The present study deals with the leading edge fences on a wing-body to decrease a horseshoe vortex, one of the factors to generate the secondary flow losses, and investigates the characteristics of the generated horseshoe vortex as the shape factors, such as the installed height, and length of the fence. The study was investigated using $FLUENT^{TM}$. Total pressure loss coefficient was improved about 4.0 % at the best case than the baseline.

• Korean Chemical Engineering Research
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• v.48 no.3
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• pp.337-341
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• 2010

The flow patterns in a stirred tank, 1m in diameter and 1 m in height, were studied using CFX, a commercial computational fluid dynamics program, with the impeller rotation speed, the impeller blade angle and the tank-bottom shape varied and the baffles included or excluded. A vortex was observed in the center of the tank in the absence of the baffles, and the intensity of the vortex increased with increasing the rotation speed. The vortex was considerably reduced in the presence of the baffles. An increase in the blade angle increased the vertical flow and decreased the vortex intensity. The flow in the corners of the tank bottom turned smoother as the tank bottom was varied in shape from flat to round.

• Aerospace Engineering and Technology
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• v.8 no.1
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• pp.197-206
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• 2009

To improve the aerodynamic efficiency of Smart Unmanned Aerial Vehicle (SUAV), vortex generators and flow fence are applied on the surface and the tip of wing. The initially applied vortex generator increased maximum lift coefficient and delayed the stall angle while it produced excessive increase in drag coefficient. It turns out reduction of the airplane's the lift/drag ratio. The new vortex generators with L-shape and two different height, 3mm and 5mm, were used to TR-S4 configuration to maintain the desired level of maximum lift coefficient and drag coefficient. Flow fence was also applied at the end of both wing tip to reduce the interaction between nacelle and wing when nacelle tilting angles are large enough and produce flow separation. To examine the effect of flow fence, flow visualization and force and moment measurements were done. The variation of the aerodynamic characteristics of SUAV after applying flow control devices are summarized.