• 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.

• Journal of Advanced Marine Engineering and Technology
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• v.21 no.3
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• pp.236-245
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• 1997

The flow characteristics of developing turbulent steady flow are investigated numerically and experimentally in the entrance region of a square duct ($40 mm{\times}40 mm$ and 4, 000 mm). The numerical anaysis are incorporated by finite- volume discretization with staggered grid system and SIMPLE algorithm. The numerical solution are compared with experimental results of mean velocity profiles, turbulence intensity and entrance length. For turbulent steady flow, the turbulent components in the velocity waveforms increase as the dimensionless transverse position approaches the wall. Thrbulence intensity increases as the dimensionless transverse position increases from the center to the wall of the duct for the developing turbulent steady flows. The entrance length of the turbulent steady flow is about 40 times as large as the hydraulic diameter under the present experimental condition.

• Journal of Advanced Marine Engineering and Technology
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• v.22 no.5
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• pp.643-651
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• 1998

Turbulent unsteady flows in the entrance region of a square duct are investigated with a hot-wire anemometer system. The velocity waveforms the mean and turbulence components of the axial velocity and the entrance length are obtained as a major characteristics of the developing turbulent unsteady flows. An inviscid flow theory is presented to describe the developing axial mean velocity profiles. A good agreement is seen between the measured and theoretically predicted values. The propagation of turbulence generated near the entrance of the square duct is satisfactorily approximated by an empirical correlation of the propagation of turbulence proposed so far. The local turbulence intensi-ty is found to be a little smaller in the accelerating phase than in the decelerating phase. The entrance length is about 60 times as large the hydraulic diameter.

• Journal of the Korean Institute of Gas
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• v.15 no.3
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• pp.53-57
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• 2011

The present study has been carried out to analyze the flow characteristics of a heat recovery steam generator with the change of inlet flow conditions by using numerical flow analysis. The inlet of HRSG corresponds the outlet of gas turbine exit and the flow after gas turbine has strong swirl flow and turbulence. The inlet flow condition of HRSG should be included the exit flow characteristics of gas turbine. The present numerical analysis adopted the flow analysis result of gas turbine exit flow as a inlet flow condition of HRSG analysis. The computational flow analysis result of gas turbine exit shows that the maximum axial velocity appears near circular duct wall and the maximum turbulent kinetic energy and dissipation rate exist relatively higher gradient region of axial velocity. The comparison of flow analysis will be executed with change of inlet turbulent flow condition. The first case is using the inlet turbulent properties from the result of computational analysis of gas turbine exit flow, and the second case is using the assumed turbulent intensity with the magnitude proportional to the velocity magnitude and length scale. The computational results of flow characteristics for two cases show great difference especially in the velocity field and turbulent properties. The main conclusion of the present study is that the flow inlet condition of HRSG should be included the turbulent properties for the accurate computational result of flow analysis.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.315-320
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• 2008

This experimental study has been conducted to investigate the effect of the flame holder on the multi-slot film cooling in the ramjet combustor. The turbulent wake which is generated by the flame holder on the entrance of the coolant flow path affects on the slot. Adiabatic film cooling effectiveness on the downstream wall of the slot exit are measured. The results show that the film cooling performance is rapidly decreased after the slot exit by shear layer and high turbulence intensity between separated flows and coolant flows.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.305-309
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• 2008

This experimental study has been conducted to investigate the installation of the vertical flame holder shape in ramjet combustor, which affects on the film cooling effectiveness. All slot position, the film cooling effectiveness decreases because of the shear layer and high turbulence intensity between separated flows and coolant flows. When the flame holder is installed, film cooling effectiveness decreases abruptly on the beginning of the slot exit region due to the mixing effect. As the blowing rate increases, the film cooling effectiveness is increased for all cases due to the augmented momentum of injected coolant from the slot.

• Journal of Advanced Marine Engineering and Technology
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• v.18 no.4
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• pp.94-101
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• 1994

실험 데이터는 급확대비 3:1 팽창의 시험관에서의 실험결과를 나타내고 있으며, 실험에 이용된 동작유체로써는 공기가 사용되었다. 입구관에서 레이놀즈수는 60,000으로부터 120,000까지 변하게 하였고, 스월강도는 0으로부터 16까지 변화되게 하였다. 균일한 열 플럭스 경계조건이 사용되었는데, 그 결과 관벽온도 및 체적온도는 24$^{\circ}C$로부터 71$^{\circ}C$까지에 걸쳐 나타났다. 플롯상에 국소 Nusselt수는 최대 열전달점에서 정점을 이루는 모습을 보여 주고 있다. 스월강도가 0으로부터 최대값으로 증가 되었을때, 최고 Nusselt수의 위치는 시험관에서 4로부터 1스텝 하이트로 변경되는 것이 조사되었다. 이러한 최대 Nusselt수의 상류부 이동은 완전 발달된 유동에서의 값보다 2.2배에서 8.8배나 많은 그의 크기를 증가시킨다고 할 수 있다.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.6
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• pp.9-17
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• 2007

This experimental study has been conducted to investigate the effect of the recirculation zone on the multi-slot film cooling in the ramjet combustor. The recirculation zone which is generated by the protrusion tip on the entrance of the coolant flow path affects on the first slot. Velocity fields, dimensionless temperature fields and adiabatic film cooling effectiveness on the downstream wall of the slot exit are measured. The results show that the film cooling performance is rapidly decreased after the slot exit by shear layer and high turbulence intensity between separated flows and coolant flows.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.12
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• pp.1635-1646
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• 1997

The nozzle length to diameter ratio of real diesel nozzles is about 2-8 which is not long enough for a fully developed and stabilized flow. The characteristics of the flow such as turbulence at the nozzle exit which affect the development of the spray can be enhanced by impinging the flow inside nozzle. The flow details inside the impinging nozzles have been investigated both experimentally and numerically. The mean velocities, the fluctuating velocities, and discharge coefficients in the impinging inlet nozzles, round inlet nozzle, and sharp inlet nozzle were obtained at various Reynolds number. The developing feature of the external spray were photographed by still camera and the droplet sizes and velocities were also measured by laser Doppler technique. The spray angle was greater and the droplet sizes near the spray axis were smaller with the impinging flow inside nozzle.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.3
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• pp.207-215
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• 2008

The heat/mass transfer characteristics on the plane tip surface of a high-turning first-stage turbine rotor blade has been investigated by employing the naphthalene sublimation technique. At the Reynolds number of $2.09{\times}10^5$, heat/mass transfer coefficients are measured for the tip gap height-to-chord ratio, h/c, of 2.0% at turbulence levels of Tu = 0.3 and 14.7%. A tip-surface flow visualization is also performed for h/c = 2.0% at Tu = 0.3%. The results show that there exists a strong flow separation/re-attachment process, which results in severe local thermal load along the pressure-side corner, and a pair of vortices named "tip gap vortices" in this study is identified along the pressure and suction-side tip corners near the leading edge. The loci and subsequent development of the pressure- and suction-side tip gap vortices are discussed in detail. The combustor-level high inlet turbulence, which increases the tip-surface heat/mass transfer, provides more uniform thermal-load distribution.