• Journal of Biomedical Engineering Research
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• v.22 no.1
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• pp.59-68
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• 2001

유체-고체 상호작용을 고려하여 다양한 복부대동맥류 모델에 대해서 맥동유동 및 구조를 동시에 해석하였다. 동맥류의 확장부 크기와 혈관벽 두께에 따라서 총 여덟 개의 축대칭 동맥류 모델을 선정하였다. 유한체적법 및 압력기반의 유한차분법을 이용하여 유동을 해석하였으며, 유한요소법을 이용하여 구조해석을 수행하였다. 동맥류의 확장부위가 클수록 최대응력은 최대확장부위와 변곡점에 해당하는 동맥류의 입구 및 출구 부분에 집중되었으며, Von Mises 응력은 최대확장부위 뿐만 아니라 동맥류의 근위부와 원위부($\pm$1D)에서도 현저하게 증가하였다. 또한 더욱 확장된 모델일수록 혈관벽은 직경방향의 변위보다 축방향의 변위가 지배적이었으며, 동맥류 원위부보다 근위부에서 큰 축방향 변위를 나타냈다. 동맥류 입구부의 미약한 와류는 한 주기동안 그 크기와 강도를 더해가며 동맥류 원외부로 이동하였고, 동맥류의 내부 유동은 압력차이가 감소하는 기간동안 더 큰 영향을 받았다. 확장정도가 심할수록 동맥류 내부에 더 크고 강한 와류가 관찰되었다. 압력차이가 최소가 된 직후 동맥류의 근위부와 원위부동맥 벽 근처에서의 역방향 유동이 관찰되었다. 대체로 혈관벽 두께가 감소한 모델과 더욱 확장된 모델일수록 벽전달률은 감소하였다. 혈관벽의 탄성에 의하여 압력차이와 벽전달률 사이에 위상차가 존재함이 확인되었다. 유체-고체의 상호작용을 고려한 연구는 다른 심혈관계를 이해하는데도 매우 유익할 것으로 생각된다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.8
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• pp.511-517
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• 2016

Three-dimensional models of stenosis blood vessels were prepared using a 3D printer. The models included a straight pipe with axisymmetric stenosis and a pipe that was bent $10^{\circ}$ from the center of stenosis. A refractive index matching method was utilized to measure accurate velocity fields inside the 3D tubes. Three different pulsatile flows were generated and controlled by changing the rotational speed frequency of the peristaltic pump. Unsteady velocity fields were measured by a time-resolved particle image velocimetry method. Periodic shedding of vortices occurred and moves depended on the maximum velocity region. The sizes and the positions of the vortices and symmetry are influenced by mean Reynolds number and tube geometry. In the case of the bent pipe, a recirculation zone observed at the post-stenosis could explain the possibility of blood clot formation and blood clot adhesion in view of hemodynamics.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.5
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• pp.109-117
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• 2002

An off-surface flow visualization experiments have been performed to investigate the flow field over a delta wing with the leading edge extension(LEX). The model is a flat wing with $65^{\circ}$ sweepback angle. The free stream velocity is 6.2 m/s, which corresponds to Reynolds number of $4.4\times10^5$ based on the wing root chord. The angle of attack and sideslip angle range from $16^{\circ}\sim28^{\circ}$ and $0^{\circ}\sim-15^{\circ}$, respectively. The visualization technique of using the micro water-droplet and the laser beam sheet enabled to observe the vortical flow structures, which can not be obtained by 5-hole probe measurements. With sideslip angle, the interaction and breakdown of the LEX and wing vortices was promoted in the windward side, whereas, it was suppressed in the leeward side.

• 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.

• 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.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.6
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• pp.1-7
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• 2005

Incompressible Reynolds-averaged Navier-Stokes equations with $\varepsilon{-SST}$ turbulence model are adopted for the investigation of the flow fields between the square cylinder and the ground. When the grounds moves, the diminish of the shear layer intensity on the ground promotes the interaction between the lower and the upper separated shear layer of the cylinder. Hence vortex shedding occurs at the lower gap height than stationary ground. In the moving ground, the secondary shedding frequency disappears due to the absence of the separation bubble on the ground which exists in the stationary ground. In addition, the shedding frequency and aerodynamic coefficients in the moving ground become higher than those of the stationary ground.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.289-292
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• 2009

Injector dynamics of multi swirl injectors in an annular combustor have been investigated by LES(Large Eddy Simulation) turbulent model with MPI parallel computation technique. The present study employs the LM6000 lean premixed swirl-stabilized annular combustor. Real shape combustor is simulated in order to investigate the detail interaction mechanism among multi-injectors. The strong vortex breakdown occurs at the impinging surface between the adjacent injectors so that the complex and strong oscillatory pressure propagates inside of the combustor. Tangential pressure fluctuation mode was captured by including multi injectors in computational domain.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.2
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• pp.26-34
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• 2009

Secondary flow losses can be as high as 30~50% of the total aerodynamic losses for a turbo-machinery blade or stator row. These are important part for improving a turbine efficiency. Therefore, many studies have been performed to decrease the secondary flow losses. The present study deals with the chamfered leading-edge at a generic wing-body junction to decrease the horseshoe vortex, one of factors to generate the secondary flow losses, and investigates the vortex generation and the characteristics of the horseshoe vortex with the chamfered height, and depth of the chamfer by using $FLUENT^{TM}$. It was found that the total pressure loss for the best case can be decreased about 1.55% compare to the baseline case.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.449-452
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• 2008

Flow difference between reacting and non-reacting case in a swirl stabilized annular combustor is investigated using 3D Large Eddy Simulation with flamelet turbulent combustion model. The combustor of concern is the LM6000, lean premixed dry low-NOx annular combustor, developed by GEAE. Boundary conditions are based on experimental data. Heat release as a result of combustion put the dilatation of density in primary combustion zone highly increased so that the main swirl stream behind of a swirl cup stretched further downstream than that of non-reacting case. The oval shape of core flow in cross-section to flow direction, which clearly observed in non-reacting case, tends to be circle, and small vorticities in wide range in non-reacting case disappears, but the size of iso-vorticity increase in reacting case.

• Journal of the KSME
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• v.25 no.5
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• pp.413-418
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• 1985

직접 접촉식 교환장치(이하 직접 교환기라 함)에서 액체의 유통형태의 선택은 매우 다양하며 전달계수 역시 개별적인 상황이나 충전물의 종류에 따라서 달라지므로 일률적으로 제시되지 못 하고 있다. 많은 경우 실험을 통하여 열전달 또는 물질전달계수를 측정하게 되나 개수로, 자유 낙하액체막, 액체분류와 같이 이상화가 가능한 경우, 이러한 전달계수를 구하기 위하여 이론적 또는 반실험적인 해석을 수행하기도 한다. 수많은 관련 연구결과들은 층류유동에 관한 것과 난류유동의 경우로 구분되고(예상되듯이 대부분의 직접교환기의 유통영역은 난류쪽이다), 난류 유통의 해석은 다시 표면갱신이론(surface renewal model), 와류확산계수모델(eddy diffusivity model-macroscopic), 미분형와류모델(differential eddy diffusivity model)로 대별된다. 여기서는 수많은 교환기형태의 자료정리보다 상기와 같이 대별된 액체측 유동영역별로 전달현상해석의 방법을 간단히 정리하고자 한다.