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곽종호(Jong-Ho Gwak),김희동(Heuy-Dong Kim) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.11
Perforated wall has long been employed to control a variety of flow phenomena. It has been, in<br/> general, characterized by a porosity of the perforated wall. However, this porosity value does not take<br/> account of the number and detailed shape of porous holes, but is defined by only the ratio of the<br/> perforated area to total wall surface area. In order to quantify the porous wall effects on the flow<br/> control performance, an effective porosity should be known with the detailed flow properties inside the<br/> porous holes. In the present study, a theoretical analysis using a small disturbance method is performed<br/> to investigate detailed flow information through porous hole and a computational work is also carried<br/> out using the two-dimensional, compressible Navier-Stokes equations. Both the results are compared<br/> with existing experimental data. The gasdynamical porosity is defined to elucidate the effect of<br/> perforated wall.
곽종호(Jong-Ho GWAK),권용훈(Yong-Hun KWEON),木俊之(Toshiyuki AOKI),김희동(Heuy-Dong KIM) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
The effects of absorbing materials on the characteristics of supersonic jet noise were experimentally investigated using a convergent-divergent nozzle with a design Mach number of 2.0. Overall sound pressure levels (OASPL) and noise spectra were obtained at far-field locations. Schlieren optical system was used to visualize the flow-fields of supersonic jets. In order to investigate the effect of absorbing materials, baffle plates of different materials (metal, grass wool and polyurethane foam) were installed at the exit of the nozzle. Experiment was carried out over a wide range of nozzle pressure ratios from 2.0 and 18.0, which corresponds to over- and under-expanded conditions. The results obtained show that the screech tone amplitude and the overall sound pressure level reduce by using the baffle plates of absorbing materials, compared with the metal baffle plate. It is also found that the characteristics of supersonic jet noise are strongly dependent on the size of baffle plate.
적외선 카메라를 이용한 초음속 충돌 동축제트의 벽면 온도 측정
곽종호(Jong-Ho Gwak),V. R. Sanal Kumar,김희동(Heuy-Dong Kim) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
The supersonic impinging jet has been extensively applied to rocket launching system, gas jet cutting control, gas turbine blade cooling, etc. In such applications, wall temperature of an object on which supersonic jet impinges is a very important factor to determine the performance and life of the device. However, wall temperature data of supersonic impinging jets are not enough to data. The present study describes an experimental work to measure the wall temperatures of a vertical flat plate on which supersonic, dual, coaxial jet impinges. An Infrared camera is employed to measure the wall temperature distribution on the impinging plate. The pressure ratio of the jet is varied to obtain the supersonic jets in the range of over-expanded to moderately under-expanded conditions at the exit of coaxial nozzle. The distance between the coaxial nozzle and the flat plate was also varied. The coaxial jet flows are visualized using a Shadow optical method. The results show that the wall temperature distribution of the impinging plate is strongly dependent on the jet pressure ratio and the distance between the nozzle and plate.
Experimental Study of the Supersonic Free Jet Discharging from a Petal Nozzle
이준희(Jun-Hee Lee),김중배(Jung-Bae Kim),곽종호(Jong-Ho Gwak),김희동(Heuy-Dong Kim) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
In general, flow entrainment of surrounding gas into a supersonic jet is caused by the pressure drop inside<br/> the jet and the shear actions between the jet and the surrounding gas. In the recent industrial applications,<br/> like supersonic ejector system or scramjet engine, the rapid mixing of two different gases is important in that<br/> it determines the whole performance of the flow system. However, the mixing performance of the<br/> conventional circular jet is very low because the shear actions are not enough. The supersonic jet discharging<br/> from a petal nozzle is known to enhance mixing effects with the surrounding gas because it produces strong<br/> longitudinal vortices due to the velocity differences from both the major and minor axes of petal nozzle. This<br/> study aims to enhance the mixing performance of the jet with surrounding gas by using the lobed petal<br/> nozzle. The jet flows from the petal nozzle are compared with those from the conventional circular nozzle.<br/> The petal nozzles employed are 4, 6, and 8 lobed shapes with a design Mach number of 1.7 each, and the<br/> circular nozzle has the same design Mach number. The pitot impact pressures are measured in detail to<br/> specify the jet flows. For flow visualization, the schlieren optical method is used. The experimental results<br/> reveal that the petal nozzle reduces the supersonic length of the supersonic jet, and leads to the improved<br/> mixing performance compared with the conventional circular jet.