• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.2219-2226
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• 2003

Two perforated plates are placed in parallel and staggered arrangements with a gap distance of 2 times of the hole diameter, and initial crossflow passes between the plates. Both the injection and effusion hole diameters are 10 mm, and the Reynolds number based on the hole diameter and hole-to-hole pitch are fixed to 10,000 and 6 times of the hole diameter, respectively. To investigate the effect of crossflow, the flow rate of crossflow is changed from 0.2 to 2 times of that of the impinging jet. A naphthalene sublimation method is used to determine the local heat/mass transfer coefficients on the upward facing surface of the effusion plate. With the initial crossflow, the heat/mass transfer rates on the effusion (target) plate decrease as the velocity of crossflow increases, since the crossflow induces the locally low transfer regions formed at the mid-way between the effusion holes. However, the impingement/effusion cooling with crossflow presents higher heat/mass transfer rates than the array jet impingement cooling with the same initial crossflow.

• 대한기계학회논문집B
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• 제28권3호
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• pp.338-348
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• 2004

The present study is conducted to investigate the effect of rib arrangements on an impingement/effusion cooling system with initial crossflow. To simulate the impingement/effusion cooling system, two perforated plates are placed in parallel and staggered arrangements with a gap distance of 2 times of tile hole diameter. Initial crossflow passes between the injection and effusion plates, and the square ribs (3mm) are installed on the effusion plate. Both the injection and effusion hole diameters are 10mmand Reynolds number based on the hole diameter and hole-to-hole pitch are fixed to 10,000 and 6 times of the hole diameter, respectively. To investigate the effects of rib arrangements, various rib arrangements, such as 90$^{\circ}$transverse and 45$^{\circ}$angled rib arrangements, are used. Also, the effects of flow rate ratio of crossflow to impinging jets are investigated. With the initial crossflow, locally low transfer regions are formed because the wall jets are swept away, and level of heat transfer rate get decreased with increasing flow rate of crossflow. When the ribs are installed on the effusion plate, the local distributions of heat/mass transfer coefficients around the effusion holes are changed. The local heat/mass transfer around the stagnation regions and the effusion holes are affected by the rib positions, angle of attack and rib spacing. For low blowing ratio, the ribs have adverse effects on heat/mass transfer, but for higher blowing ratios, higher and more uniform heat transfer coefficient distributions are obtained than the case without ribs because the ribs prevent the wall jets from being swept away by the crossflow and increase local turbulence of the flow near the surface. Average heat transfer coefficients with rib turbulators are approximately 10% higher than that without ribs, and the higher values are obtained with small pitch of ribs. However, the attack angle of the rib has little influence on the average heat/mass transfer.

• 대한기계학회논문집B
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• 제29권7호
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• pp.828-836
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• 2005

Impingement/effusion cooling technique is used for combustor liner or turbine parts cooling in gas turbine engine. In the impingement/effusion cooling system, the crossflow generated in the cooling channel induces an adverse effect on the cooling performance, which consequently affects the durability of the cooling system. In the present study, to reduce the adverse effect of the crossflow and improve the cooling performance, circular pin fins are installed in impingement/effusion cooling system and the heat transfer characteristics are investigated. The pin fins are installed between two perforated plates and the crossflow passes between these two plates. A blowing ratio is changed from 0.5 to 1.5 for the fixed jet Reynolds number of 10,000 and five circular pin fin arrangements are considered in this study. The local heat/mass transfer coefficients on the effusion plate are measured using a naphthalene sublimation method. The results show that local distributions of heat/mass transfer coefficient are changed due to the installation of pin fins. Due to the generation of vortex and wake by the pin fin, locally low heat/mass transfer regions are reduced. Moreover, the pin fin prevents the wall jet from being swept away, resulting in the increase of heat/mass transfer. When the pin fin is installed in front of the impinging let, the blockage effect on the crossflow enhances the heat/mass transfer. However, the pin fin installed just behind the impinging jet blocks up the wall jet, decreasing the heat/mass transfer. As the blowing ratio increases, the pin fins lead to the higher Sh value compared to the case without pin fins, inducing $16\%{\~}22\%$ enhancement of overall Sh value at high blowing ratio of M=1.5.

• 대한조선학회논문집
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• 제31권3호
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• pp.47-58
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• 1994

본 논문에서는 천수역에 위치한 선박의 선형(線形) 조종성 계수를 추정하기 위한 이론적인 해석법에 대한 연구가 수행되었다. 세장체 이론을 사용하여 선체 주위의 유동을 모델화하였으며, 이로부터 물체 근처의 내부 유체 영역에서의 횡방향 유속에 대한 적 미분 방정식을 유도하였다. 이의 수치해법에 관하여 자세히 기술하였고, 특정 경우에 대한 이론해와 계산 결과를 비교하여 그 타당성을 검증하였다. 이 적 미분 방정식의 해를 이용하여 선체의 선형(線形) 조종성 계수를 추정할 수 있다. Mariner. Series 60, Wigley 선형에 대한 계산을 수행하였으며, 기존의 실험 결과와 비교하여 보았다. 조종 운동을 하고 있는 선체 주위의 복잡한 유동을 모델화하는 과정중에 포함된 여러 가지 가정에도 불구하고, 계산 결과는 실험 결과와 정성적, 정량적으로 잘 일치하며, 선박의 초기 설계 단계시 수심에 따른 기본적인 조종성 변화를 추정할 수 있을 것으로 생각된다.