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정사각 막냉각홀 내부에서의 열/물질전달 및 유동 특성 (II) - 비대칭 입구조건 효과 -
이동호,강승구,조형희,Rhee, Dong-Ho,Kang, Seung-Goo,Cho, Hyung-Hee 대한기계학회 2002 大韓機械學會論文集B Vol.26 No.7
An experimental study has been conducted to investigate the heat/mass transfer characteristics within a square film cooling hole with asymmetric inlet now condition. The asymmetric inlet now condition is achieved by making distances between side walls of the secondary now duct and the film cooling hole different; one side wall is $2D_h$ apart from the center of the film cooling hole, while the other side wall is $1.5D_h$ apart from the center of the film cooling hole. The heat/mass transfer experiments for this study have been performed using a naphthalene sublimation method and the now field has been analyzed by numerical calculation using a commercial code. Swirl now is generated at the inlet region and the heat/mass transfer pattem with the asymmetric inlet now condition is changed significantly from that with the symmetric condition. In the exit region, the effect of mainstream on the inside hole now is reduced with the asymmetric condition. The average heat/mass transfer coefficient is higher than that with the symmetric condition due to the swirl now generated by the asymmetric inlet condition.
변형된 단일 막냉각홀 주위에서의 열/물질전달 및 막냉각효율 특성
이동호,김병기,조형희,Rhee, Dong Ho,Kim, Byunggi,Cho, Hyung-Hee 대한기계학회 1999 大韓機械學會論文集B Vol.23 No.5
Two problems with jet injection through the cylindrical film cooling hole are 1) penetration of jet into mainstream rather than covering the surface at high blowing rates and 2) nonuniformity of the film cooling effectiveness in the lateral direction. Compound angle injection is employed to reduce those two problems. Compound angle injection increases the film cooling effectiveness and spreads more widely. However, there is still lift off at high blowing rates. Shaped film cooling hole is a possible means to reduce those two problems. Film cooling with the shaped hole is investigated in this study experimentally. Film cooling hole used in present study is a shaped hole with conically enlarged exit and Inlet-to-exit area ratio is 2.55. Naphthalene sublimation method has been employed to study the local heat/mass transfer coefficient and film cooling effectiveness for compound injection angles and various blowing rates around the shaped film cooling hole. Enlarged hole exit area reduces the momentum of the jet at the hole exit and prevents the penetration of injected jet into the mainstream effectively. Hence, higher and more uniform film cooling effectiveness values are obtained even at relatively high blowing rates and the film cooling jet spreads more widely with the shaped film cooling hole. And the injected jet protects the surface effectively at low blowing rates and spreads more widely with the compound angle injections than the axial injection.
연소실 냉각을 위한 충돌제트/유출냉각기법에서 유출판에서의 열전달특성
이동호,조형희,Rhee, Dong-Ho,Cho, Hyung-Hee 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.3
The present study is conducted to investigate the local heat/mass transfer characteristics for flow through perforated plates. A naphthalene sublimation method is employed to determine the local heat/mass transfer coefficients on the effusion plate. Two parallel perforated plates are arranged for the two different ways: staggered and shifted in one direction. The experiments are conducted for hole pitch-to-diameter ratios of 6.0, for gap distance between the perforated plates of 0.33 to 10 hole diameters, and for Reynolds numbers of 5,000 to 12,000. The result shows that the high transfer region is formed at stagnation region and at the mid-line of the adjacent impinging jets due to secondary vortices and flow acceleration to the effusion hole. For flows through the perforated plates, the mass transfer rates on the surface of the effusion plate are about six to ten times higher than for effusion cooling alone (single perforated plate). More uniform and higher heat/mass transfer characteristic is obtained in overall region with small gap between two perforated plates.
베인과 블레이드 사이의 상대위치 변화에 따른 터빈 블레이드 표면에서의 열/물질전달 특성
이동호(Dong-Ho Rhee),조형희(Hyung Hee Cho) 한국유체기계학회 2004 유체기계 연구개발 발표회 논문집 Vol.- No.-
In this study, the effect of relative position of the blade for the fixed vane has been investigated on blade surface heat transfer. The experiments were conducted in a low speed stationary annular cascade, and heat transfer of blade was examined for six positions within a pitch. Turbine test section has one stage composed of sixteen guide vanes and blades. The chord length of the tested blade is 150 ㎜ and the mean tip clearance of the blade having flat tip is about 2.5% of the blade chord. For the detailed mass transfer measurements on the blade surfaces, a naphthalene sublimation technique was used. The inlet flow Reynolds number is fixed to 1.5×10^5. Complex heat transfer characteristics are observed on the blade surface due to various flow characteristics, such as separation bubble, relaminarization, transition to turbulence and leakage vortices. The distributions of velocity and turbulence intensity change significantly with the relative position due to the blockage effect of the blade. This causes the variation of heat transfer patterns on the blade surface. The results show that the flow near the leading edge get highly disturbed and deflected toward the either side of the blade when the blade leading edge is positioned close to the trailing edge of the vane. Therefore, separation bubble disappears on the pressure side and overall heat transfer on the relaminarization region is increased. But, due to reduced tip gap flow at the upstream region, the effect of leakage flow on the upstream region of the blade surface is weakened. Thus, the heat transfer characteristics significantly change with the blade positions.