• Proceedings of the KSME Conference
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• 2007.05b
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• pp.1888-1893
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• 2007

In this study, the microchannel plated heat exchanger were numerically studied for the enhancement of heat transfer in the channel configuration. Unit cold and hot fluid region with the microchannel were modeled and periodic boundary condition at the side wall was applied to continuously repeating geometry. The material of micro-structured plate is STS304 and working fluid is water. Triangular obstacles were placed in micro channel to enhance heat transfer. The performance of microchannel plated heat exchangers were numerically investigated with various obstacle configuration and Reynolds number under the parallel and counter flows. Heat transfer rate has increased about 18% compared with straight channel, but pressure drop also increased about 3.5 times. The main factor of increasing of pressure drop and heat transfer rate is considered that the momentum was lost to collide against obstacles, generation of secondary flow and boundary layer separation, wake and vortex forming phenomena.

• 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.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.223-226
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• 2006

Computational Study of a sphere subjected to free stream flow and simultaneously subjected to spinning motion is carried out. Three dimensional compressible Navier-Stokes equations are solved using fully implicit finite volume scheme. SST(Shear Stress Transport) $k-{\omega}$ turbulence model is used. Aerodynamic characteristics being affected are studied. Validation of the numerical process is done for the no spin condition. Variation of drag coefficient and shock wave strength with increase in spinning rate is reported. Changes in the wake region of the sphere with respect to spinning speed are also observed.

• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.194-199
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• 2007

IB (immersed boundary) method is one of the prominent tool in computational fluid dynamics for the analysis of flows over complex geometries. The IB technique simplyfies the solution procedure by eliminating the requirement of complex body fitted grids and it is also superior in terms of memory requirement. In this study we have developed numerical code (FOTRAN) for the analysis of 2D flow over a cylinder using IB technique. The code is validated by comparing the wake lengths and separation angles given by Guo et. al. We employed fractional-step procedure for solving the Navier-Stokes equations governing the flow and discrete forcing IB technique for imposing boundary conditions. Also we have developed a 3D code for the backward-facing-step flow and flow over a sphere. The reattachment length in backward-facing-step flow was compared with the one given by Nie and Armaly, which has proven the validity of our code.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.1166-1171
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• 2009

Fin-tube heat exchangers are widely used in refrigeration systems. To improve the performance of fin-tube heat exchangers, the shape of plain fin was developed in slit fin and louver fin. These pins have higher heat transfer performance as well as larger pressure drop. Recent studies of a delta winglet vortex generators(DWVG) show less heat transfer capacity than louver fin. However, the DWVG have very small pressure drop. This paper compares the performance for the plain fin and DWVG fin in terms of flow characteristics and heat transfer based on CFD analyses. The DWVG generate vortex and delayed flow separation and leads to a reduction of a wake region behind a tube. The results show that the DWVG produce improved heat transfer and reduced pressure drop compared to a plain fin. This result is opposite to the Reynolds analogy.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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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

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.1
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• pp.83-89
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• 2002

In the present study, heat transfer characteristics of oil flow over offset strip fins were predicted by the numerical methods. Oil flow in the plate-fin passage was idealized by 2 dimensions. The flow patterns and heat transfer characteristics were predicted in details. Numerical results shows that the average convective heat transfer coefficients are almost independent on the raws of fins and affected by fin pitches. At the rear face of fin, there exists minimum point of heat transfer coefficients where stream are separated from the fin surfaces. The convective heat transfer coefficients were effected by separation bubbies which appeared at the wake region of offset strip fins.

• Proceeding of EDISON Challenge
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• 2012.04a
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• pp.85-88
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• 2012

루프 페어링은 화물차의 주행저항 및 유도항력을 줄이기 위해 설치되는 장치 중 하나이다. 이 장치는 화물차의 지붕 윗부분에 설치하여 화물차가 받는 항력을 줄이는데 사용이 된다. 이번 과제에서는 루프 페어링의 효과에 대해 유체역학적인 증명 및 확인을 위해 루프 페어링의 설치 전-후 트럭의 형상에 따른 유동의 변화와 항력계수의 값을 EDISON CFD를 사용하여 구한 후 각각 비교 하였다. 이를 위해 EDISON CFD의 압력 contour와 stream line, 정압계수(Cp)그래프를 통해 트럭의 주행 중 발생하는 박리현상을 가시적으로 확인하였고, 항력계수(Cd)값을 비교하는 것을 통해 루프 페어링을 설치한 경우가 미설치된 경우보다 주행 시 더욱 유리하다는 것으로 결론을 내렸다.

• Proceeding of EDISON Challenge
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• 2012.04a
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• pp.41-44
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• 2012

본 연구에서는 풍력발전에 충분한 가능성을 가진 산악 지형을 모델링하여 유동의 흐름을 분석하였다. 실제 지형(설악산, 점봉산)에 대한 1/500 축소모형을 Gaussian 함수로 표현하였다. EDISON_CFD을 사용하여 산악지형의 난류유동을 해석하였으며, 해석결과의 신뢰성 확인을 위해 격자분해능에 따른 속도분포를 비교하였다. 산악지형에 따른 유동현상을 속도분포 및 유선함수 등에 의해 분석하였다. 또한 풍력터빈 설치 높이 기준에 의거하여 지형변화에 따른 주 유동방향 속도분포를 살펴보았다. 지형효과에 따른 유동해석결과를 기반으로 풍력 발전 가능 영역이 논의되었다.

• Journal of the Korean Society of Visualization
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• v.4 no.2
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• pp.51-58
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• 2006

A boundary layer visualization was carried out in order to investigate the influence of Reynolds number on an oscillating airfoil. An NACA 0012 airfoil is sinusoidally pitched at the quarter chord point with oscillation amplitude of ${\pm}6^{\circ}$. A smoke-wire technique was employed to visualize the boundary layer and the near-wake. The freestream velocities are 1.98, 2.83 and 4.03m/s and corresponding chord Reynolds numbers are $2.3{\times}10^4,\;3.3{\times}10^4$, and $4.8{\times}10^4$, respectively. As the reduced frequency of K=0.1 is fixed, the corresponding frequency of an airfoil was adjusted in each case. The results reveal that the point at which the shear stress in an unsteady boundary layer separation disappears does not correspond with the position of the breakdown of the boundary layer, and that the breakdown of the boundary layer occurs further downstream.