• 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.

• Journal of the Korean Society of Combustion
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• v.18 no.3
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• pp.68-74
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• 2013

가스터빈용 희박 예혼합 연소기 내부에 와류 발생기(vortex generator)를 장착하여 그에 따른 연료/공기혼합 및 NOx 배출 특성 변화를 조사하였다. 이를 위해 수치해석적 방법을 채택하여 연소기내 유동특성, 연료/공기 혼합도, 배기가스(NOx), 화염형상을 분석하였다. 와류 발생기를 장착한 경우, 연소기 내부에서 와류 발생기에 의한 나사산 형상으로 인해 와류가 형성되며 이는 연소기 전면부까지 유지되었다. 또한 연소기 내부 면적 차로 인해 압력섭동이 발생하였다. 이와 더불어 연소기 전면부 기준 상류지역의 연료와 공기의 혼합도가 증가됨으로서 연료 과농지역이 감소하게 되며 이로 인해 전반적인 NOx 발생량의 감소 효과를 볼 수 있었다. 화염 형상의 변화로부터 와류 발생기의 영향으로 선회수는 다소 감소할 것으로 예상되며, 이는 와류 발생기로 인한 유속의 반복적 증감에 의한 결과라고 판단된다.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.33.1-33.1
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• 2005

• Journal of Aerospace System Engineering
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• v.14 no.3
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• pp.1-9
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• 2020

In this paper, the effects of the delta winglet vortex generator, the airfoil vortex generator and the guide vanes on the friction factor and the Colburn factor in the fin-tube flow were studied. The vortex generator and guide vane were non-dimensionalized based on the channel height and tube diameter, and locations were selected according to the authors' suggestions. The Reynolds number based on the inlet velocity and the tube diameter was selected in the range of 1400-8000. As a result, the friction factor resulted in a 4.7% decrease in guide vanes at the Reynolds number 8000 over the conventional fin-tube, and the Colburn factor resulted in a 33% increase in the delta winglet vortex generator at the Reynolds number 3800 over the conventional fin-tube.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.483-486
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• 2008

Numerical Simulation was performed to investigate the role of vortex generator. Vortex generator installed on the upper surface of the wing, generates vortex flow, mimic the external flow with boundary layer flow and transfer energy from outside to wall boundary. Vortex generator, thus, retards the flow separation and increases the lift and drag of the wing.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.4
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• pp.28-34
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• 2019

In this study, pin-fin arrays, which are widely used for cooling turbine blades, were studied. The vortex generator in pin-fin arrays is located in front of the circular tube. The cross-section of the vortex generator is NACA-9410. The purpose of this study is to analyze heat transfer performance and flow characteristics of pin-fin arrays. The position of vortex generator is changed with the vertical flow direction on the bottom wall. Pin-fin arrays were calculated with 6000, 10000 and 15000 Reynolds number. The commercial program ANSYS v18.0 CFX and the turbulence model $k-{\omega}$ SST were used. As a result, the heat transfer performance increased up to 5.8% and pressure loss increased less than 1%.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.197-201
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• 2006

In the development process of a fuel-rich gas generator using kerosene and LOx for a 30 tonf class liquid rocket engine, a heat damage occurred at the LOx post of swirl coaxial injectors used in the gas generator and the problem has been examined. To prevent the heat damage, injectors are redesigned to have an increased recess while maintaining internal mixing, which minimizes recirculation region to prevent anchoring of the flame in the recirculation region. The combustion test results of the sub-scale gas generator showed that this scheme can prevent heat damage of the LOx post in the swirl coaxial injectors of the fuel-rich gas generator.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.2
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• pp.87-94
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• 2003

To reduce the air side pressure drop in air-cooled heat exchanger, tow-in type winglet vortex generators are applied. A specially designed multiple-channel test core was used in the experiments for the various geometry of winglet vortex generators. The proposed tow-in type vortex generator gives significant separation delay, reduces form drag, and removes the zone of poor heat transfer from near-wake of the tubes. The results show the significant pressure drop reduction for the tow-in win91e1 vortex generators with the similar enhancement of the heat transfer as other vortex generator applications in heat exchanger. In the range of Reynolds number of 350 to 2100 the pressure drop decrease 8∼15% and 34∼55% for the in-line and staggered tube banks, respectively, compared to those without vortex generators.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1447-1452
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• 2003

Vortex is very interesting flow phenomena on the heat transfer enhancement. In the present study, naphthalene sublimation technique is used to determine the average and local mass transfer coefficients on the flat plate with vortex generator. A parametric study with Reynolds number and angle of attack is carried out to investigate the heat transfer enhancement. The heat transfer coefficients on the flat plate with rectangular type and delta type vortex generator are compared with those of the flat plate without the vortex generator. Comparing heat transfer coefficients between rectangular type and delta type vortex generator, rectangular type vortex generator has much higher value than delta type vortex generator at the same condition.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.107-110
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• 2002

The present study deals with CFD analysis of 'The vortex generators on plastic plate heat exchanger'. When a vortex generator is placed on the heat transfer surface, the flow gets more complex because it entails complicated three-dimensional flows such as separation, reattachment, and recirculation. CFX-5.4, a commercial code utilizing unstructured mesh, has been used as a computational method for solving RANS(Reynolds-Averaged Wavier-Stokes) equations, and the applied turbulence model is $k-{\varepsilon}$ model. In addition, those computational analyses were implemented under various conditions , with or without the vortex generator between two plates, the number, form and the size of vortex generator, and different attack of angle. From the calculated temperature, velocity and pressure distribution, vorticity, wall heat flux and so on under those conditions, this study shows the effect of vortex on heat transfer.