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이삭(Sak LEE),이동원(Dong-Won LEE),김병지(Byung-Ji KIM),권순범(Soon-Bum KWON) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
Jets issuing from a conventional nozzle and convergent nozzles of a constant expansion rates and a certain normal using an annular slit are compared to investigate the characteristics of the 3 jets. In experiments, to compare the characteristics between jets, the nozzle exit mean velocity is fixed as 90㎧. The pressures along the jet axis and radial directions is measured by scanning valve system moving with 3-axis auto-traverse unit, and the velocity distribution can be obtained by calculation from the measured static and total pressures. To obtain the highly stable and convergency jets, a nozzle has to be designed with an annular slit connected to an conical cylinder, furthermore, the flow through aconstant expansion rate nozzle using annular slit is the most probable. And the pressure drop along the nozzle for the constant expansion rate nozzle is small.
이동원(Dong-Won LEE),신승영(Seung-Young SHIN),김병지(Byung-Ji KIM),권영두(Young-Doo KWON),권순범(Soon-Bum KWON) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
To control the coating thickness of zinc in the process of continuous hot-dip galvanizing, it is known from early day that the gas wiping through an air knife system is the most effective because of the obtainable of uniformity of coating thickness, possibility of thin coating, working ability in high speed and simplicity of control. But, the gas wiping using in the galvanizing process brings about a problem of splashing from the strip edge for a certain high speed of coating. And, it is known that the problem of splashing is caused mainly by the existence of separation bubble at the neighbor of the strip surface. In theses connections, in the present study, we proposed two kinds of air knife systems having the same expansion rate of nozzle, and the jet structures and coating thicknesses from a conventional and new proposed nozzles are compared. In numerical analysis, the governing equations consisted of two-dimensional time dependent Navier-Stokes equations, standard k-ε turbulence model to solve turbulence stress and so on are employed. As a result, it is found that it had better to use the constant rate nozzle from the point view of the energy saving to obtain the same coating thickness. Also, to reduce the size of separation bubble and to enhance the cutting ability at the strip, it is recommendable to use an air knife having the constant expansion rate nozzle.
응축을 수반하는 정상 2차원 초음속 노즐유동의 수치해석
김병지 가톨릭상지전문대학 1997 논문집 Vol.27 No.1
For the supersonic circular nozzle flow with condensation the effect of the stagnation specific humidity on the quantity of state and the condensation shock wave is investigated by numerical analysis and experiment the results are summarized as follows ; The nonequilibrium condensation zone glove form to two dimensional shape with the of felt of geometry. The increase of the stagnation specific humidity escalate the extent of its zone. The condensation shock wave is located in the nonequilibrium condensation zone, its location moves to the upstream and its shape becomes gradually to normal condensation shock wave, with the increase of the stagnation specific humidity. It is confirmed that the point of onset of nonequilibrium condensation be corresponded to the point where the static pressure deviates from that of isentropic process and the nucleation rate is maximum.
영각을 가진 미소진폭 파형벽을 통한 응축을 수반하는 초음속 유동
김병지 가톨릭상지대학 사회개발·산업기술연구소 1999 論文集 Vol.29 No.-
미소진폭 파형벽을 따라 응축성 기체인 습공기가 초음속으로 흐르는 경우 미소진폭 파형벽의 중심선이 주류에 대하여 임의의 영각을 가질 때의 유동장에 대한 유동특성을 구명하고자 파형벽에 의한 경사충격파의 발생, 정체점 상태량이 유동특성에 미치는 영향, 영각에 의한 유동특성의 변화 등을 고찰하였다. 초음속 풍동, 슈리렌 시스템 및 수은 마노메타 등의 실험장치를 이용하고, 가시화 사진 및 정압측정으로부터 실험결과를 얻었다. 또한, 응축을 고려한 직접진행형 특성곡선법에 의한 수치해석을 수행하였고, 실험결과와 비교함으로써 정체점 상태량과 영각의 변화에 따른 경사충격파의 거동과 유동장 상태량의 변화를 확인하였다. Supersonic flow with condensation are of great importance in diverse fields of science and engineering such as high speed aircraft, rocket nozzle, combustion chamber of gas turbine, ram jets, steam turbine cascades, and so on. Condensation in supersonic flow give rise to the corrosion and erosion, degradation of mechanical components and equipments, as well as efficiency reduction and energy losses in steam turbine cascades. The characteristics of supersonic flow with condensation along a wavy wall of small amplitude with an attack angle in a channel was studied numerically and experimentally. Flow properties in the flow field was calculated by the direct marching method of characteristics. The very complex problem that may appear where the overlapping of the same family characteristics occurs, can be satisfactorily solved by means of the modified method suggested by Zucrow. Intermittent indraft supersonic wind tunnel was used as an experimental apparatus. The flow field was visualized by schlieren system. Static pressure distribution was measured by Hg-manometer and flow properties were obtained by the assumption of isentropic process. Especially, the dependency of the locations of reflection of oblique shockwave generated by the wavy wall, and distributions of flow properties in the flow field, upon the stagnation conditions and attack angles was clarified.
미소 진폭 파형벽을 가진 유로내에서 凝縮을 수반하는 定常 2次元 超音速 流動
權純範,金丙知,安亨濬 慶北大學校 1992 論文集 Vol.52 No.-
The characteristic of the steady two-dimensional supersonic flow with condensation along a wavy wall of small amplitude in channel is investigated through the direct marching method of characteristics. The very complex problem that may appear where the overlapping of the same family charateristics occurs, can be satisfactorily solved by means of the modified method suggested by Zucrow. In the present study for the case of supersonic moist air flow, the dependency of location of formation and reflection of oblique shock wave generated by the wavy wall, and distributions of flow properties, on the relative humidity and temperature at the entrance of wavy wall is clarified by plots of frozen Mach number and iso-flow properties. Also, it is confirmed that the wavy wall plays an important key role in the formation of oblique shock wave, and that the effect of condensation on the flow field appears apparently.
미소 진폭 파형벽을 가진 유로내에서 응축이 수반되는 초음속유동의 Prandtl-Meyer 팽창에 관한 실험적 연구
권순범,안형준,김병지,선우은 경북대학교 산업기술연구소 1993 産業技術硏究誌 Vol.21 No.-
The characteristics of the Prandtl-Meyer expansion of supersonic flow with condensation through a channel with a small amplitude wavy wall are investigated experimentally. In the present study, for the case of moist air flow in the type of indraft supersonic wind tunnel, the dependency of formation and reflection locations of the oblique shock wave and the distribution of flow properties are clarified by flow visualization and pressure measurement with the variation of the specific humidity and temperature at the entrance of the wavy wall and the attack angle of the wavy wall to the main stream. Also, we confirm that the wavy wall plays an important key role in the formatio of oblique shock wave, and that the effect of condensation on the flow field appears apparently.
膨脹率이 一定한 超音速 노즐흐름에 있어서 非平衡 凝縮과 傾斜衝擊波
권순범,최태민,김병지 慶北大學校 1990 論文集 Vol.49 No.-
In the present study the case of expansion of moist air through a supersonic nozzle of constant expansion rate, which behaves similar to that of wet steam, was adopted. The effect of noneqilibrium condensation on the oblique shock wave generated by placing the wedge into the supersonic part of the nozzle was investigated. Furthermore, the variation of the condensation onset Mach number with the initial stagnation supersaturation, the relationship between noneqilibrium condensation zone and incident point of the oblique shock wave, the varation of angles of incident and reflected shock waves due to the variation of initial stagnation supersaturation, and the relationship between the height of Mach stem and initial stagnation supersaturation are discussed.