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주기적인 통과후류가 막냉각되는 평판의 유동장에 미치는 영향(1);압력면과 흡입면에 대한 영향(1)
국건,이준식,고상근,Kuk, Keon,Lee, Joon-Sik,Kauh, Sang-Ken 대한기계학회 1996 大韓機械學會論文集B Vol.20 No.6
The effect of periodic passing wake on the film-coolant flow issuing normally from a flat plate was investigated experimentally. The passing wake was generated by rotating thin circular bars. Depending on the rotational direction the test plate could be simulated as a pressure surface or a suction surface of a gas turbine blade. The phase-averaged velocity components were measured using an X-type hot-wire probe. The Reynolds number based on the free-stream velocity and injection hole diameter was 23, 500 and the velocity ratio which is the ratio of film coolant velocity to free-stream velocity was 0.5. The velocity-triangle induced by the wake was similar to that induced by the one generated at the blade trailing edge. The vertical velocity component induced by the passing wake, which approaches to the suction surface and moves away from the pressure surface, played a dominant role in the variation of the flow field. The variation in the phase-averaged velocity on the pressure surface was greater than on the suction surface, but the turbulence kinetic energy variation on the suction surface appeared larger than on the pressure surface.
자유유동 난류강도가 원형 곡면위의 분사홀 상류에서의 막냉각에 미치는 영향에 대한 연구
서형준,국건,이준식,이상우,Seo, Hyeong-Joon,Kuk, Keon,Lee, Joon-Sik,Lee, Sang-Woo 대한기계학회 1994 대한기계학회논문집 Vol.18 No.3
The leading edge of a turbine blade was simulated as a circular cylindrical surface. The effect of free-stream turbulence on the mass transfer upstream of the injectionhole has been investigated experimentally. The effects of injection location, blowing ratio on the Sherwood number distribution were examined as well. The mass transfer coefficients were measured by a naphthalene sublimation technique. The free-stream Reynolds number based on the cylinder diameter is 53,000. Other conditions investigated are: free-stream turbulence intensities of 3.9% and 8.0%, injection locations of $40^{\circ}$, $50^{\circ}$, and $60^{\circ}$ from the front stagnation point of the cylinder, and blowing ratios of 0.5 and 1.0. The role of the horseshoe vortex formed upstream edge of the injected jet is dicussed in detail. When the blowing ratio is unity, and the coolant jet is injected at $40^{\circ}$, the mass transfer upstream of the jet is not affected by the coolant jet at all. On the other hand, when the injection hole is located beyond $50^{\circ}$, the mass transfer upstream edge of the injection hole suddenly increases due to the formation of the horseshoe vortex, but it dereases as the free-stream turbulence intensity increases because the strength of the horseshoe vortex structure becomes weakened. The role of the horseshoe vortex is clearly evidenced by placing a rigid rod at the injection hole instead of issuing the jet. In the case of the rigid rod, the spanwise Sherwood number upstream of the injection hole is much larger due to the intense influence of the horseshoe vortex.
이유섭(You-Seop Lee),국건(Keon Kuk) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11
Crosstalk between adjacent channels is well known in thermal inkjet print heads. Excessive crosstalk can cause drop velocity and volume variations that result in poor printing quality. Thus, inkjet heads should be designed to minimize the crosstalk effects between adjacent channels. This paper presents lumped modeling and numerical studies of crosstalk characteristics within thermally driven inkjet print heads. The inter-channel crosstalk of the thermal inkjet head is investigated using the lumped R-L network model and numerical simulation. It is found that reducing restrictor width can reduce the jet crosstalk by viscous damping. The degree of crosstalk has been quantified using the value of cross-correlation between velocities of ink at the actuated channel and neighboring one. Critical dimensions of the restrictor for acceptable crosstalk have been determined by using the lumped model in a good agreement with the numerical simulation results. The present modeling and simulation can be used for a better design of thermal inkjet print heads to minimize crosstalk effects.