• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.8
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• pp.677-684
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• 2007

In the Present Study, a 3-D viscous flow solver, based on unstructured hybrid meshses containing tetrahedra, prisms and pyramids, has been developed. A finite-volume discretization scheme is used for solving the compressible Navier-Stokes equations. A cell-vertex median dual volume is used for spatial discretization. The one-equation Spalart-Allmaras turbulence model has been adopted to evaluate the eddy viscosity. Validation were made by computing laminar and turbulent flows around a 3-D wing for steady flows and turbulent flows around an oscillating 3-D wing in harmonic motion for unsteady flows.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.12
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• pp.2368-2375
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• 1992

The transition of turbulent kinetic energy(TKE) balance along the centerline of the flow unit, which is composed of straight-duct, contraction and free-jet, has been investigated by the hot-wire anemometry. It is found that the mean turbulent kinetic energy is balanced by the dissipation in the internal flow region ; by the production and the dissipation, through contraction ; and by the dissipation, in initial region(X〈8D) of free-jet. But in the developing region (8D〈X〈20D) it is balanced by all of the three(ie, diffusion, production and dissipation). Finally, in the downstream of free-jet, the mean TKE is balanced again by dissipation like as the beginning. The decay-laws along the centerline are checked in the region of free jet as well as in the straightduct. After the developing region of free-jet also exist the decay-laws, the exponent of the axial turbulence being bigger than of the radial.

• Journal of Power System Engineering
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• v.16 no.1
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• pp.44-50
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• 2012

팁 간격의 크기가 냉각탑용 축류팬의 성능과 누설 유동에 미치는 영향을 조사하기 위해서 서로 다른 2가지 팁 간격을 가진 경우에 대해서 점성유동을 해석하였다. 케이싱 내에서 작동하는 축류팬 주위의 유동을 연속방정식, Navier-Stokes 방정식 등을 지배방정식으로 사용하여 수치해석 하였다. 난류유동에 나타나는 레이놀즈 응력은 ${\kappa}-{\epsilon}$ 난류모델을 사용하여 계산하였다. 전체적으로 H형 격자계를 사용하였으며, 팁 주위의 유동을 해석하기 위해서 팁 영역 주위에 부분적으로 조밀한 격자를 두었다. 팁 간격이 증가하면 누설 유동의 증가로 인한 유동 손실의 증가로 전압상승과 수력효율이 감소하였다. 팬 직경에 대한 팁 간격이 0.4%에서 1.0%로 증가하면 전압상승 값이 약 10% 정도 감소하였으며, 수력효율은 약 3% 정도 감소하였다. 팁 간격이 팁 근처 날개 주위의 압력에 미치는 영향을 보면, 팁 간격이 증가하여 누설 유동이 증가하면 흡입면과 압력면의 압력차가 전연 부근에서 감소함을 알 수 있었다. 누설 와류의 중심은 코드를 따라서 흡입면으로 부터 떨어져 나가면서 형성됨을 알 수 있었다. 누설 와류의 위치를 보면 팁 간격이 증가하면 와류 중심의 위치가 흡입면 쪽으로 이동하고, 흡입면에서 떨어진 거리도 날개 후반부에서 증가 폭이 커지는 포물선 형태로 증가함을 알 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.6
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• pp.1269-1281
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• 1989

본 연구에서는 H를 고정하고 L을 변화시켜가며 내부의 유동구조가 어떻게 변하는가를 살펴보고, 특히 재부착이 일어나는 경우에는 급확대 부분만 존재하는 기존 실험결과와 비교분석하여 하류의 급축소부분이 전체 유동구조에 어떤 영향을 미치는가를 살펴보고자 한다. 실험에서 사용된 작동유체는 공기이며, 입구관 직경은 110mm, 급확대점과 급축소점사이의 연결부 직경은 220mm, 연결부의 길이는 L=300, 600 그리고 900mm의 3가지를 선택하였으며 기준속도는 입구관의 중심속도로 9.71 m/s이다. 입구직경(110mm)을 기준으로 한 Reynolds 수는 $R_{e}$=73,000 이고 입구관반경과 연결부반경의 차이인 계단높이(H=55mm)를 기준으로 하면 $R_{e=36}$ ,500이다. 연결부 의 급확대부분에서 입구관반경을 기준으로 한 반경확대비는 2이고 급축소부분의 반경 축소비는 1/2이다. 측정항목은 유동방향의 벽면압력분포, 유동방향의 평균속도분포 및 난류강도 등이며, L=900mm인 경우는 반경방향과 원주방향의 난류강도, Reynolds 전단응력도 측정되었다.

• 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 the Korean Society of Propulsion Engineers
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• v.18 no.2
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• pp.1-9
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• 2014

To investigate the flame dynamics in an annular combustor with single swirl injector, a 3D large-eddy simulation (LES) and a level-set flamelet turbulent combustion model have been implemented. The LM6000 developed by GEAE has been used as the combustor of concern and boundary conditions are based on experimental data. The strong central toroidal recirculation zone induced by the volume expansion of the combustion gas and the vortex breakdown continuously occurred through the procession of the vortex with decreasing strength, are observed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.5
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• pp.731-740
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• 2001

A numerical study on the quantitative analogy between the fully developed turbulent flow in a straight square duct rotating about an axis perpendicular to that of the duct and that in a stationary curved duct of square cross-section is carried out. In order to clarify the similarity of the two flows, dimensionless parameters K(sub)TR=Re(sup)1/4/√Ro and Rossby number, Ro, in a rotating straight duct flow were used as a set corresponding to K(sub)TC=Re(sup)1/4/√λ and curvature ratio, λ, in a stationary curved duct flow so that they have the same dynamical meaning as those of the fully developed laminar flows. For the large values of Ro or λ, it is shown that the flow field satisfies the asymptotic invariance property, that is, there are strong quantitative similarities between the two flows such as flow patterns and friction factors for the same values of K(sub)TR and K(sub)TC.

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.3
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• pp.25-32
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• 2001

A passive control method of the interaction between a weak normal shock-wave and a turbulent boundary-layer was simulated using two-dimensional Navier-Stokes computations. The inflow Mach number just upstream of the normal shock wave was 1.33. A porous plate wall having a cavity underneath was used to control the shock-wave/turbulent boundary-layer interaction. The flows through the porous holes and inside the cavity were investigated to get a better understanding of the flow physics involved in this kind of passive control method. The present computations were validated by some recent wind tunnel tests. The results showed that downstream of the rear leg of the $\lambda$-shock wave the main stream inflows into the cavity, but upstream of the rear leg of the $\lambda$-shock wave the flow proceeds from the cavity toward to the main stream. The flow through the porous holes did not choke fur the present shock/boundary layer interaction.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.67-70
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• 2008

Production and dissipation of turbulent structure in a swirl stabilized combustor was investigated using three-dimensional Large Eddy Simulation analysis. The combustor of concern is the LM6000, lean premixed dry low-NOx annular combustor, developed by GEAE. Inlet condition was based on experimental data. Strong vortex breakdown in main stream, vortex ring proceeding downstream, and the turbulent structure periodically oscillating have been observed. Reasonable agreement was obtained by comparison of the results with experiments and previous LES studies.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.7
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• pp.32-40
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• 2003

An experimental research has been carried out for flow visualizations of the shock wave/turbulent boundary-layer interaction control utilizing the aeroelastic flaps, Spark shadowgraphs, kerosene-lampblack tracings for the surface streakline pattern, and interference fringe patterns over a thin oil-film applied at the downstream of the shock interactions have been obtained , Effects of variation of the shapes and thicknesses of the flaps are tested, and all the results are compared to the solid-wall reference case without flow-control mechanism , From the qualitative observation of the variation of skin friction utilizing the interference fringe patterns over the silicone oil-film, a strong spanwise variation of the skin friction with a narrow and long region of separation has been noticed near the centerline behind the shock structure, which phenomenon demonstrate a strong three-dimensionality of the shock interaction flows, Influence of the shape of the cavity under the flaps to the shock interaction is also tested, and it is observed that the shape of the cavity is not negligible.