• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.359-366
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• 2000

A numerical study has been performed for the 2-dimensional film cooling employed in the cooling of hot components such as gas turbines. The flow and heat transfer characteristics are numerically simulated using FLUENT software. Blowing ratios vary from 0.25 to 5.0 and coolant injection angles vary from $15^{\circ}\;to\;60^{\circ}\;in\;15^{\circ}$ increment. The result shows that, for all cases, there exists a blowing ratio which maximizes film cooling effect (measured by the distance from the slot exit to the downstream wall location at which temperature increases to 900 K) for a given injection angle. It is also observed that the film cooling effectiveness decreases when downstream wall is sunk or lifted. The simulation has been performed using both constant properties and temperature dependent variable properties. It is found that the cases with constant properties overestimate the film cooling effect considerably.

• 대한기계학회논문집B
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• 제24권6호
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• pp.870-879
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• 2000

An experimental investigation is conducted to improve a slot film cooling system which can be used for the cooling of gas turbine combustor liner. The tangential slots are constructed of discrete holes with different injection types which are the parallel, vertical, and combined to the slot lip. The investigation is focused on the coolant supply systems of normal-, parallel-, and counter-flow paths to the mainstream direction. A naphthalene sublimation technique has been employed to measure the local heat/mass transfer coefficients in a slot with various injection types and coolant feeding directions. The velocity distributions at the exit of slot lip for the parallel and vertical injection types are fairly uniform with mild periodical patterns with respect to the hole positions. However, the combined injection type increases the nonuniformity of flow distribution with the period equaling twice that of hole-to-hole pitch due to splitting and merging of the ejected flows. The secondary flow at the lip exit has uniform velocity distributions for the parallel and vertical injection types, which are similar to the results of a two-dimensional slot injection. In the results of local heat/mass transfer coefficient, the best cooling performance inside the slot is obtained with the vertical injection type among the three different injection types due to the effect of jet impingement. The lateral distributions of Sh with the parallel- and counter-flow paths are more uniform than the normal flow path. The averaged Sh with the injection holes are $2{\sim}5$ times higher than that of a smooth two-dimensional slot path.

• 대한기계학회논문집B
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• 제29권1호
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• pp.46-54
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• 2005

Film cooling characteristics has been examined numerically for the height variation of a stepped slot exit. In this study, the upstream wall height of the stepped slot exit varies from -2d (d = slot width) to 3d, blowing ratio ranges from 0.5 to 3, and injection angles are $15^{\circ},\;30^{\circ},\;and\;45^{\circ}$. The results showed that film cooling performance was mainly subjected to the magnitude of recirculation region near the downstream-side slot exit as well as the magnitude and the distribution region of turbulent kinetic energy due to the local velocity and momentum differences between the coolant and the main flow near the slot exit. The up-1d type slot at higher blowing ratios over 2 and the flat type slot at lower blowing ratios below 1 have the best film cooling performances, in case of the injection angles of $30^{\circ},\;and\;45^{\circ}$, respectively. Compared with the other injection angles, in case of the injection angles of $15^{\circ}$, the best film cooling performances was shown in even a higher upstream wall (up-3d) at higher blowing ratio like 3 by the gradual reduction of the coolant velocity which minimizes the local velocity differences between the coolant and the main flow near the slot exit.

• 한국유체기계학회 논문집
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• 제20권2호
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• pp.5-10
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• 2017

In this study, the Coanda effect inducing bump was applied to improve the film cooling effectiveness on the flat plate with $30^{\circ}$ and $45^{\circ}$ angled rectangular slots. The slot length to width ratio was 6. A cylindrical cap shaped structure, called Coanda bump, was installed at the exit of the slot to generate Coanda effect. The width and height of the bump was 10.5 mm and 1 mm, respectively. The film cooling effectiveness was measured at the fixed blowing ratio, M=2.0, using pressure sensitive paint (PSP) technique. The mainstream velocity was 10 m/s and the turbulence intensity was about 0.5%. Results showed that the film cooling effectiveness for case of $30^{\circ}$ angled slot was higher than that of $45^{\circ}$ angled slot. It was found that there was no positive effect of Coanda effect on the overall averaged film cooling effectiveness for the $30^{\circ}$ angled slot. On the other hand, for the $45^{\circ}$ angled slot, the film cooling effectiveness was improved with the installation of the Coanda bump.

• 한국산학기술학회논문지
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• 제17권11호
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• pp.363-367
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• 2016

본 연구는 마하수 2.5의 초음속 영역에서 마하수 1.0의 슬롯 분사가 있는 후향계단 형상에 대한 유동장 특성을 분석하기 위하여 초음속풍동 시험부를 설계, 제작하였다. 비행체가 고속으로 움직일 때 공동 주위의 유동은 매우 복잡하여 수치해석 결과를 검증할 초음속풍동 시험 자료가 필요하기 때문에 기존의 2차원 대칭형 노즐을 아랫면이 평판인 비대칭형 노즐로 수정하였다. 특성곡선해법을 이용한 비점성 노즐을 설계하고, 시험을 통해 얻은 경계층 두께를 노즐에 반영하여 보정한 기법을 C 언어로 프로그래밍하여 얻은 결과를 수치해석 결과와 비교하여 검증하였다. 슬롯 분사 시 지속적인 유동장 변화 분석을 위한 초음속 유지시간 확보를 위해 저장탱크의 압력 변화에 따른 PID 제어프로그램 수정으로 초음속 유동 유지시간을 약 5초에서 약 6초로 1초 정도 연장하여 제어 효율을 향상하였고, 슬롯 분사가 있는 후향계단에서의 유동장 변화를 슐리렌장치로 가시화하여 복잡한 유동장 특성을 확인하였다. 향후 슬롯 분사의 속도와 유량, 유동장의 온도를 변화하여 공동에서의 막냉각 효과 분석을 위한 장비로 사용할 계획이다.